Voicu, Dolocan - Fizica jonctiunilor cu semiconductoare

i0I

or*J1ffieiu3t+rcl*s

ilr-r1lu1rn cs
acl e;r .usacnu .p1u;-r1d,u "qHlautnlfrisiul1a?:itn-c;".trio.lTrJila#rlufgl?.rJrdrtsJ,;il.r-',';irj,1, c'fqif$uj (a
crJ+colarp Iili€J+s
oJ
rg?roi'gd:BJr).1lr1.rtI'aro3BJcn.ilJrErrr_rrl-t,.crrir€l*.i)=zl['.rrparp*rlsooro;prraqTulrolodrJgatIurlpl+l{aol.'sr.rU.p{rua'arruxa}3cudrrlud,Nl_urldnuup€larrnqizr1laIaaaroJlrdT€dl'iod.Io,+IuuiBl1),3rrrJr.IuJridJau.oaot(cr/ri+gU+u1g{nr.C€d€uutlrn'_wflEouqI1cca?ai'l<rc(rllpc.{tnlarrro.plgusiualol.'.n[uoroIcL+n]al+.noa,pBlrla?rssorllupun.t€rrlladi}nrr.r,Dil?irperrururoa\cr.rd;rc{li+l"oa]is{e:utuI.g{fcararluqdsi-rcno,ouoo?rdc.aau-ruop,psdriuau+Jpuil*+r+sur:r)sri-sJfnxtac.roorDrl€pouso..a€rlprrrerr+irsiaaouuiuTll1rcA1rodo,n.rtrTlspei-p.rio-rqgorupzsp,orrloarrrsr+rl.ap?siJroruelo1a,ecir.r'i.rcr-lro,1riicl"rcrosa,lra1rsir,or.i-irirduasur+rnhricsnrgaioap"11,uj:.sleca.rauer,1lcu'€1orrru:p,L3rprouil
Ilir
e?-orIiJrn{r.{lr{ir)r;.rrar+upsoropi?usuaarrploonJ+cuslrxrrneIEnrj.Juru,rluo?auicdra,Tsaaur.li?"uiuagrarap:rr,r,a\:[cJ)konqor";f-riaeoau6'rr,r0grp1u1fruc.nEjdna*odl-)ag1o],el,oi1urtuas1,oiqd+oiKliscrllraJapi,rr1.crudorl1riJ1rirp+:6us
N
-?gu?ar''rranu?nnilaqlubniillon]r"clnlr'rt,rie-rriJJuLlcriudersllt.oorT;eBr'urr|for.,)orrroj"aict,)l'r"ups-s{p,n1e.iaErrrrsrlo{lrZaiarllE'dnr(roa+Iru'pcrlr.uI',,ur{rnulrnJnancoIlosl'stJaIucs1DlnIuoar't0ndlDlrd"*uJaururt+Jo',arnufrJlr'saTBmtruoa."+l^aenoJslea.{uprm?lJnIurloubnra+E1uara'aSJglrudu_oiocw1uurrllocnluEgr's,e,aarrricp1nr){r1lT;f{lr"}eouslpr,uug'1ssi6cc.irnnu;ernr:ulaur{cp.yunzr,Ipns,uaio}go)r.crarriDlagdri.trria}rla{r:ip1n,)c,1,i,lpnp"rar,aEuf:oigcuui,ar;1r:rsi.r,rig/sc1plt's]al"ol..dr1"r$u,pagizjpruisrop.acur1mr,n1r,?rlurotusTo1oor.api0r-,"pr,rna..rlrri'uIro"ilcJ[l+auA,orotli"aispit{-ll_g1,r*L,)ltr1rr.r,l-:,|1i.a)unr;l.rrorliiJpuc.11+S+e?roiirll-rc,r,,,rllir'.ozraro,aeunal"l;r1-.rr,il,lr,
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,{ Irli+s op o+,u}rsLrcp oE+srxa g;l t,:a,r;rr{nc{nso;rc{ ut,Fsnp]l} a3.sa ill.i,u1or !};-,BaD}.-
?rr
/ r , c,'c,) n:f.r', ldtLbior) ,g OII

' -t as

ouriclo cs rsor[n on" a,ru] {o

oJo-tosrtuolrsJltzo?'ulp^forrrersluuJI€ocniltzz1utcJ=j+rarrrr.r'_crfa.fris'ugc'g,Filelgru/p'.ui-p.urqdIunns6lucgtaaatrp0ju*rrt-.o=lJa?,upo:{\ist\ari.!or6un0o'rp1o1iutr0l,grr,sr.:iut;lrngtat.u/r:r.,Ur.1rcgi{rn3oIs.d*n-spAIur.rlio0lgapIZprr,.sr6rio6r:c0+t=trai.:Til,i.drg,tu.lgJlruol1uriJa'irqcn!Teo. .)p
tl
(rg'e) t(#i)," u'l-l + +:'
AS
:pu"rr
:tfv r.r ouii<1o as q(g?iglo.pg)€tF*lz(Su,')Su) Jo.gnrlicr:l1uararxuaipoq(('fa.rgrS).raerria{upnd,;nap) g ar
a1a.r;s1p oloaru irrol
T+
-s:eixr nrincir.qsrp e1leouuo as Earp li?urnu aaeg ag.uorl cs (gt'gi uliu1a,i.rl1i yjr3
-€;dn"'op rJE:l.r ap rr:i-qlrsuap na.nlrrru.ro,lap rl qiu.r:.ldns aliripl,s ap €d113+rsrrop \trt
3p 1]oJrp'rlud:Jl .r.trsa "'fl p,irtrerdns ap i)[{rlr}s ar{ op uurar,ug 'lzeolq5arr as ,-lrla,rp
IlrJqlualu u{p uiir uar{rrJ} L:.rn.rl<d.l irz.ranaF ir! . I-I
'u?.t:}u",r'ecl ltlulr+In EJ laJ+n-r3
-I-\
{se'e) (?.+)"".J 1--r#fu 'l1r

- ;,Jv "f pldgp pr - ria
(zl'qd-) r{xa - a,ruur.rn urrr{ r.i AldVd lrJ?su
pa q?lnzar +e?raprsuoc Inzqrc ul ols
(ore)li (grg) urp oin

Ilri

Jls
IIIJ

OJ
11.r

-uJ
lrp

-I]

-III
'Hi

OS

A doua problemil cle rezolvat este legatfl de curentul de deplasare

dintre electrodul cle cimp qi probd, care apale in special ia inaltS, frecvenld,1
influen!,a acestui curent trebuie eliminati,. O solulie pentru a' minirnaiiza

-t

I+

I
I
I
i

.'; 11
l
l{ 'T-

lL

Figt.lui3.1s0t.u-dirrCl icrcfeucittuulludi ccicbaczirrn"rpp. eir- FIlcign't.l'u:1.s1I1u.d-iul(lcirfccuclirtiu]ul i r'n purrte
ilt cinrir.

infl'.rcnla cLuentului de depla,sar'o a,supra semnalului de mXsurat este folo-

sirea unui circuit in punte, reprezentat in figura, 3.11. fnilial puntea se

echilibreazi, cu ajutorul rezistoru.lui -E qi al capacitS,lilor, astfcl ca semnalu-l
pe oscilograf sii fie minim. Aceasta inseamni, c5, cursntul de cleplasare se
distrilruie in mod egal pe celc cloui, intr5,ri alc amplificatorului diferenlial.

fn tirnpui acestei operatii nu trece curent continuu prin circuit. Se trece

apoi curent continuu prin circuit ;i se rnlsoani pe oscilograf semnalul

tlatorat efectului de cimp. Ca sL se evitc incd,lzirea excesivX a probei cincl se
lucrea,zd, Ia curenli rnari, in iocul bateriei cle curent continuu se folosegte
un generator cle pulsuri cle curent. l\{obilitatca tle efect de cimp sc deter-
minti clin rela!,ia

do

c;L,: J' drro'
-

unde O este capacitai,ea pe unitatea de arie intre trlcctrodul tle cirnp Ei
probii. Evaluarca concluctanlei de suprafa!5, din mtisurd,tori se face dup5,
crr'rrr rumeazX. R,eferindu-ne la figura 3.10 notiim cu R rezistenla probei,
cn J?, rezistenla restului circuitului probei, ca Vo tensiunea tle cimp, cu
i3fit,!ft1uennt'esai:unpEeroaEl:!ee@lie, cvt*raormfiat"ol)itao, a-cEroe',nsaicclbusacittnaetnrfileueini $cpilircooubdoeesi etprm.e".nuNanlouitltianmdtei.,sacuurda-ett pe rezistenla

lungimea Di t
pre-
arie in
zenla falri de absenl;a cimpului este
:++{,#-#}\o{,..) :+{#.") *#}
(336)

Dac'ii ).P, F, itotiucl I^ - E lR,, rezulLva din rcla!,ia de mai sus

Ao- La (3.3 ?)

I*nz'

102

80r

kv't) 'uvs : uv fuv + od + ou,)';-:'.tr

dv : zt'v rulued eur{qo es 'rtrV * 0d : d'u V * :,zt, ?, pulgoli

ela,rru od 'piuJr:Jdns c*p.aI 'ij .FIC (ft'g) '(d 0a du)rL -'.a
B.lruirrqluoJaLI
-

^,r/illdLsriI,q-d U;;xlh#flf'tr1fi*i:Tfu#i
I (ofle) :'d i :'it'
-'un1moFloac,u,rrrqcu".su4lprc6.(l-or'?coldodd'ucaamrs*aZgsTiru.yofup".t.'o,rdoc,r?.l1lS,nansr?nt1pn,rlaoopJl rau1urr.p-[r
,;r _G_-T .l_ ,, L
____i_1 sAb
9---.-S-!-1t- rac rS p{e3e"rdns el ap rruoJ+oolo o"r+u.i n"Tq E

-jrTqca op .ror a{rro{€d ,',r0lrrl ir*"a*,(,a,J,criuttr"q*ui?ro"?ffail.#ol;p'}&In,?Tu3ar;c5r}:a.$oTc ,c"+J.qido ?"L.-;HeptruJn n
e1 alir{u.4ua;liloa 1qs tI

(oe's) t(slf,soy _tdtu)t),:t1 V,

ar,rcs altocT es iuln1o,.t nrlued er{u1a.r nc eiSolerru nr.r6 I(

(se's) :( s,1, bbtrt' _ df0-- -
a
LL
a
,?i,ue--ge"dacr.aredugr6lnu1usrri'dyqqtesuiqIe+rcooaplJarurro.der1Jpunnu{:+lorliuJureeB.rro"JDnrnc1lcaozi:clstlocoge1up.pupn11€+C(+.r,€aEn'r;Jrcs'p;lrEauoa1oa1prdcupnos€Ip1nrtu:"Jptgop;p11crumr"nr.und'cdnuo3asnp":r.coi"xn"+en1acpIrJts:d-p1ru"nuuriroful1flcfoniqtur#mqIJpfa.#{ioel,"rysreoead;zrnccrulrnu"?s1,e:Ii€leaeloTpc;qenas.prrryrodur+?cno1ssaT7a
I
g{ere"rdn.s €I Tr"rgrnclruoaa.l ,c{uaza:td 'urnloa rri rrJrgurqtuoaa;i eldnse eurmop
o
gs e1uod g{ugu.rdns €I €aJe{rrqrrroaal r.rr{qns rrn+€J+s uI 'rnlnJo+cnpuocruras
{nurnlorr uI raJ"rrrquroaal nc So1uue pour ul girle.ir{ns ap Jolala,\ru InTpat{ .I

-Jo?ur ur.ril rS col 'saa€ oleod Errr?Jtss ap JoIrJo+,K1rncI re.reurqruoaag e
Ir
piugu.rtlns ul Bd.rurrrqtuoaag'g'g e

€ g?tsuiur*!.{roD TaJ}I€ 1r13s r+tsprxo u{e;e;rclns ed aede ,rdrtt?;tiT?;iHntt#Hl -

e{e;u"rdns ec{ a1ua1r.rpls p+sixo nrr gc Arsg8 u-g 'aprde.r aIIrEls 1lcap Sunl iuur v
11nur c{urrq un-"r}ur g{ua1el ap rS or{cnpuoc op allzuaq nc gurcrqss ep r"roqgitr.rnd
gqu4qcs olrral olrr9lg 'eprde"r aloc op o1ue1 "gfuye.rdns op ollrgls eoeurgsrp e op it

oI'lsgnsr{du"roy./cruns"seruldnIInd+cs€€uoJ."mrpesdsJ'u!eon4{IrurcJeIgn,or?lcp€sau"q€rr';ucooorrsJsJ"ooraaa+aplrgrzprour€rpqp3.r"I qrlutos{rpur+.raroK";gsrraln.nr;urosrpcs9kauld{gou's0c4a:c1"(nAgor)pp0n,e+?-,cIsa+Jn(a€"lJgoAnpusa)opcdImr:JpoIinz+}€lFt[saJuzarltrspupEra+nIsn. A

S : r."{lo * ?o i- Arz,) are climensiunile unei vitcze qi sr,: nutucqte vitczir,
la suprafalli tlcnsi-
de recornbi,rriu'e 1zl, suprafa!5,. Consieleriim rui crristil o
tatc. ,I', rle nir.cle .situate la tlistanla ,O, de rrrargitLe:l infelioarli a lrltrzii tle
concluclitr. Ratcle cle capturii ale electronilor ;i, rcsl)LrLrtir., golurilor pe ii,ceite
nivt'le .qe scriu
t'n : lnlnr{-}- -- t") * nrttrl,
{jl.t.:i j
t " : -1i11lps??, ?r(il - ?r").1'

ut'ttlt' -o ;i i' sittl' coef.icicnfii tle capturl, a r:lcc1;ronilor, 1i, r'es1rt:r:tir'" {oLi-
clectronilor pe stri.lile tlrr
liirx ia,r ??,. esle couceittlrtia rml;lafa1.l-"-r

111 : !"11-Lrlt'7, ?r : -Yre-(Ls-LtllttT. r:i.-l{ I

In tonclilii sta{iorta,ret ?',, : 't'u : 't'., se oir{inc

"' r- - - t":;:1,(pu - porrp) 1li. ii r
-..r(tt. ., ri,) -r- -.,n(lr" , Ill)

unr'le r,, qi p.. sint, tlate clc rela,!,i1, (3.40). Cornparind" (3.45) cu i3.42) se
obtine

r\ .: -1-'i,r'r':, po*noj-An (3.46 )

"(,?1.r * 1,r,hz * \fitg9'Ns * T, lo"-to"

Se tibservr"l cii viteza cle lctotnbinare la suprzr,fa{ir, dcpinde de r.illoarea,
''}" rr, irotenli:r,lului dr: suprafrr,til si d.e conccntr:llia pultillorilor exces, Aril,
ccna{iir, (3.2i).Pcutrtr ci)nc€rntratii rnici ale purtritorilol cxrres, snu tlopincle

ppdmeeelrinlsll,nirrn'rI.rllir"Yot(noi1ptl1ic,lloo:-llilrei^dtftee,ttlc,oip'te.uc.G':oflttrte,r:rf-liirglninr[ir6ryl,i1ril'rc.ljl(-.sl:'trei,,,slirru''sucpcslirpllrreel,fpct1ltlleililirzp,iilrn,ir1nnt,rinciR,g,t1eo8ml7er/o..i\isr',nLef,eurp&,rtrriiocndazeifrntnoitnalricxlgeilncizrtnlitil,rtu1a8setcncap,l",ytt,..",
In figrlra, 3.1i1 a sint lcplrz(llri:l1.e rni,suriltolile la 24 ole d.upir, decaparea
prohei i:r,r in figulu, 3.13 l, Ia, rioLril siiptittriirti tlLrpii, ttccapare cind. stalca
s*-it,Es)hllil;lT;ilizcagat.,lCc,LLrrr6bc,1le pline sint ctlcrulatr: clupd, rela{ia (3.a$i
suirri:r,fclei 1)) 5,:i (c,urh* 2)qi5,,2 (curba 3).
(curLr*
peirtrrr (8,
tRsac,arendzceunirrtairl,ipcl isiduvcpittereaozf:epl,faer,1ri.'ct,c9r/e;Ii1co,r,1r"en*lareilntsaate..l:'leoaolcanessstntaelrinrirtr'i,aifallolndt,'ijeutlsartuctolfrovitaafllltocerrcisiqe.tne,'sl,i,iibriui"ini:iucTiaup,?ts"raalu-i
celuilalt, din ultirnii doi teuneni de la numitorul lelat,iei (3.46). Explicr*{;ia
fizir:ri, estc unniitoalea. Iial,a tle recombinare este lirnita,t[ de captur:l pur-
tritr:rilor: (elerrtroni sau goluri) (,&ro &u vite,za de rccombinare cea ma,i micil.
Pent:'rr t]l" { 0, in semiconductorul d,e tip tt benzile sint inclinate in sus,
la inclinarc puternicii, :lpilre stlat cle inversiune tsi captura electronilor este
lirnitrr,t,:i cle nurn:irul rnic rle elcct,r'oni clin r-olum cara pot sd, escalacleze bariera
inryri:-sliini :altjcunigri'Xjolsa, sulr:lfa{,il. Pe de alti ptlrte, pentru t" > 0,
dc potonfia,l
benziie sint :l,prlre aslfel strat c1e acrtrnulare de electrorri
cir,1rt,nra, golurilor oste linlil,atfl, tle liumiirul mic do goluri, ps) (are pot si,
i{:'rarii,ajruihrrilrgzliirii,l,edcisnuuripaolllru,ifaamll,i[:l,iasmsenesprtlreiuailfunaifplug. eaDrnoalastohlrniifcidioie' ncajluctlpor-ertnltcoilire.an,litenlsi opsrucblri,tiepi rulntlicdseeupidcrelnrn,pfaionttderi,nr,il-ii

104

SOL

€I (gg'g) illrr5,itirrr op oirr+rpuot (t) :- 6 niulll;dti:i {:J 1.l1iliJ1,1i' ill Jt,ll.to}'tl.
-,rncl t oJ,I]uIixnll rr1,rc[ o.nz;aua.8 ep rlri,tl.r,.; 1I;] l)trr]t)\J'i)rznJIp .lp liqtli)i;tl]oo.]
nilrlr {f roi lrrnlo,\ rrr rirr{.),i.ur. ixl .r{)Ir,rol'r'1,rnt[ ,u gi,Llr^l cir ltrdr:ny o]s'd r i)puii

,1 r :.' r,\ L ,!iQ ? {l 1

a__ l/f-i, u dif f , I

lIV i
i
'(r/5 : i)r,rJS Jrr ol,n+rrrilrluoc +rp UrirD,rir rlrqn.]fr15.)L{ ,r,r,}Jr)I,) rh.ur.r ir,,i1rlir.1
ri ruorlcola uV 'yt =- 6 tr:i.JJ,e.rdn..r tI o,rut.tntrillr ur,rrl ,rrzu; r- I
-raluI rr.y) r.rnlo.irdy clrl op e,rtoiiDrip{rorliuri)ii'rtyo,rtl I
o-,riu.r l1:) lt,rtlprsr.ro't o\-
Jn' (f'f'g'fi;)d
'di)|J.r()oi rJ JIJzStl rirJulldxa 'uleluairrr,ratlx.) t]l)o)..)irr ,)i,rl:-,)J) rir rl) i)]In?{riT

"e.nrinrirlir iir,rtl a;lu; o1{ ^llrrro.it|s op ,l0lr,iol"1,rltI llli;i;l'ur rr;rl),It rrriri.)liiruoi
-o+oI'i:tpoJaui trr,rtT 'l.]rlrur.ri)-iop a.i,tot[ lts 'uitt]tr,rtIr-t'r t;t d,Iru{ri{1iit(irr.t i}p ,Ezo}t]\

oU''ri.';lrIl)nIir)st,iTotltun1ol.dtutlrittr1uoi;lursoruJl;irJttl.'1Lnll1o,,ltiJalct'[urhtrr^rIrrrstr|(l;l1)r.rr'p1rilillrfl)rialq'iilu.ntrr,:rll]ucSDdltn,l,rntpQ'.idr{r,otulJroi'trlisrrlil'lF,lriqIt)r.rriI-,t-nlt1lrL.)plsSsirr?.rsllurlrrrr,iiIrl,-trpstatip:lrl1trr;r"r'rlplfl',.lrlrti"nlrpnii,suirloL;r,t11rgr,i'*t[rri...]i,uiir;lu,nli'rrUot.rrr1.igt);o?ut1ior.ar1{r,irri
-1rr);) tjtoJ,r?.111:''!.!r{r ilrp 'Prriiir,Ioiap as "1 'clrttrl rittla,rtt u1 "1 iri s illi,1?o.lr.tJII:^?rrr

,|,tlltr-.lr)Ju illsa [,r't,u.nrbr; ur ]t?']il;.rz;)Jt[ir,r 1;r;t,r,:.r ;trJt;,r.ti Il-irlrl in ,'r :yir.rrui.rirclx,r

'l /i uir:.1r:lilirs uI Nlrii.rir\ilr] .rrri.t,riirri nrrrir,r;1 ...!.,1
) cllrtir(urtlt 'l.It?o.jJnl)Lii).)ilr.)s i)iic.r(i
'l t 1;

i< a
:-f

/'r- .--7-7 '/l zl
P^:-]ry('-.-,.!L-i------'lL +' jl ,/
:,J L

rp'1:1i;.1uJdrr:; s.,

l-t.lt0idlrui,irtrtlioUdlil.rrrr.tI.tr]rj;ilulttll.ig.il1u,itl('lt\itrti)l:I)-f,'.n1u,)ilr)\'islri'[:r{,,r)]rlr.i,,\ilr{}lir'i.\:i ci iril
1: i l

q o D
Sjtilab
,'a-,.1b
---5i-/V-/r--r-;--rAb O

:

a ",. n

I'D

suprafala neiluurinatX Ei, respectiv, iluminat5, se scriu :

ll:0, D- "}-L':n8Arl

dll

(3.48)

?t-rlt Da!" -G-sArr.
dg

In condi{ii stalionare se ob-tine

Ln: Glsh(ylL) * ^ich(uIL)1 (3.4e)
s[(1 + i\sh(d,ll) f 2"1ctt(d,lL)l '

unde -t :V D, Si T : DlLS.ln aceste cond"ilii varia.tirl, conductanlei este

dat5, de expresia

AG:\,\,,W:

: , (3.50)

unde -4 : e (liitmn *itirV,:r)(ld. lAL)ce>as1tdq, iex(dp,rleLs)ie< poa,te fi sirnplificatd, pentru
doud, (dlL) =
cazuri J.. fn primul caz, ch
- sh (dlL) )1 qi ecualia (3.56) se reduce la

#(ac)o: "",, (3.51)

unde timpui cle viafi, efectiv ette rlat de expresia (3.52J

1-!+4.

,te! r L

ln cazul (d,lL) < 1, dezvoltind ln serie funcliile ch qi sh clin relalia
(3.50), se obline

(AG)o : dAG(y + dlzL) (3.53)

b,St(l * y') (d,ll) * zy}

ACcinetalsiti,(ex1preecsuiealpiaoa(3te.5f3i)sdimevpilnifeicadteS,foinrrndaou(53,.5c1a)zucuri :

La, (3.54)

Tor d

Cinti y; 1, adic5, y*dlzL qi y2)1r ecualia (3.53) se reduce, de ase'
rnenc& la (3.51) cu
1 l- 2/S
(3.55)
TeITa ta

L06

iiiiii
il

201

ar1 eaunrsuafi '?nur+uoc ounrsua+ op €sJns o nc r* eqo;rd nD alJos ur Jo+BrzoJ (
(
un-J+urp +rn?r+suoc a+so In+rncrr3 'reqo;rd r{.ugr.rdns urp eunr{rod o acl epea (
t
K+qnpour EurrrrnT 'q gT'g uln8rr u[ +ts+uozoJdo"r also luquaullladxa 1nfeluo1q

(eg'e) '(r,,p-a - r) o(pV) : 0V
lf :e"ra1Se"rc ap eaunrf;rod e4 'plg6 + r r':,/1 opun

(ag's) '(r'rlt-) dxeo(gry) : gV

rer{.cnpuoaoqoy

tg-s€u?aIsrrauopnrtspl+rnsaoqpeqe€oaour.1dn€r{+?.izraotrsd+ocmenrprruucnos1capaesl(sfe?gc'rrgp3)rpyuK'1(rO{ulagnJ'cg+e)sulmctlus{ana;t+rdFsxo'r(tgo, tpw'S.+rn't5poi(yoO)lsVre);rr'ng-:q",rnaedpuuounrgi

{rg'e) '(t lt-) dxa rBry - ey

nc uunxoldu alrod os (89'g) ulsa.rdxa oJurrrJn urJd
'DIuu u nc rruaur"ral nc or{u.reduroc ug prdt.r l€ur csoJcsop Tcop r* parur rrur
dt'u(rg11va)prrEulo1uutra.+rasr1rocgJ1i nu rc rcrru ruur aler{rur rJol€a n€ ga rtsurnu nu 'aJ€iu a nc
sns l"eur
?+ts,rc ap durl oI) Jola+u€+suoc BzII€urs*

...tu ,t ,6: u ';z-zn-(r-u)G+ I1

(og'e) pL-

at

^s'6-T-T
{/}Inzor (;,9'g) u,it1o;r ulg 'errrr %
nc HuorrrJa?. ntsp o pV q er{nqr.rluoc
eFre.ruoc (gq'g) eg{.u1e.r mp trras ?c o.reru l€ru €ec 'altuun ug.rd 1S prdr.r

?+€r€ er,iula;r ?url?1n E?s€acy

(as'e) 'rt(r-wrr/o\ toi, - r+u\Llulr+,un=-'"pOYv

u,

olnvJ" u nJ+uad

(ss'e) '(rll-) dxa 'py K: ,O

j,, e1'ros eleocl es

(z,s'e) ",(#)*
n#TT :...(V (t ,6: 1,, ,
: .j * +uc , ,:"rC

(gs'e) IS O/Sp : d 'p"c: 'tl apun

#:' "' "* ":# ! ud)nT!i'i?,u\f#d - z') r ('r -/ 1 ) dx "r'S' v( r ) *

tOl elsa rlfenca rogsac€ e1{n1og

m'1,'laseusrtaetidiirpeectropzriospteonrf!i:ol nE:tlsecuapAlGic,iizprsctfpelldccriiledivncrp''ro,icrfaiulcnaelae unui oscilograf.

ti.c ciderc u lui
7a se cletermitr[' r,r. Intnrcit in crpresia hii cr, intervin cz] necunosrlute
,: ;i s, se f:i,c,m[sur6tori pe douz"r, probc din acela,li nr,aterial cu aceca;i stare a
sriprafelei tli-r,r' cle grosirni diferite. Astfel vor rezult& cloui, ecuafii pentru
:"y 7 t1E undei se tleterrnin[, c qi ,S. Trebuie avut in r.cticre ca lungimcii, .supra-
fcle,i iinminate si fie mult rn:li nr:tre dccit lrrngimea c1c diftlzie a pult:itorilol'
de sarcini, pentru ca efec,tele de margillc sil fic neglijabile. De ftsenrcncrr,,

atrsetbfeuliec&(jtarcleuansgtzi-mr cluangpirmoeirciinr(pfiigir.fit3::.r1p4)risniir.fiiteczlsludfiecietnlrtifrtt,retrllr:It'E().

Lumina

vv

'"l".J-l-[-l-

n]rfl*,/t-"*'

+t

G

Iriil. :i.15. -- f'trlsnrilc de hulllnir si Lr'trslLtttr':t rlurnral:i vlrialici conrluciltirlri
cu iluminarc:r (t); rtoirtlrjul trpi'rittirrrtal il').

,ir tlunn tiirrptrLultnrir.inullctiet'il.titrrl,ttlrk,r-irtlii.,li't.;lstll irliirnii t't:l'in!j
se pottel't:rr,lizil,apiicintl pe probiL un cirrpcit r,.rtti nii,-,, :tstfcl {'r,r' purr;tori i
tle rllrcinri sir lrrcornbite fuLaintc t1e a, pir,r'lisi irlobil. l{otim, rle zr,s{-}1}ronea.
incrz"r, r-l,coltl ctr relali:r, (3.51) concluctanfa in sii-rlr sttfiorralli (aG)o.,si der';
rlrnplit;udilLea lui 1''. estc proportiona,iii cu 8. Tchniir:,r, ililsr'l:iior poilte f r
ntilizatil :ttit in rnetocla foiorroncltrc{iei cit si itr nretEriia, bomb:rrciirlii r:u
palticule oli irjeclie ltr, con1,u,r:1,.

Dc o iinportanfir, deosetiitl'nste sensibiliza,i'cir firtocrlncluciir'i pl'ir:

ir,ctivarea, sLrprafelei in l,tntosft'rir, gaz-oar.:1,. Printr'-o asenlcrrcltr nretoclir, s-li,
leuryit o crofl{.)r'c a fotoi,natluoiivinllii slratelor';rubi;il'i dc su]furi de pluuii

1cloerctilteevsauoprti'*if1ii0f[1.inCj[t1ito1r-u1l4g].risc;te stut{ii ryi r*zl;ltatr rrrr,enttr a..qnpr:),stlli-

BIBI, IOGJIAFIi.]

1. \'. J)olocan. l:i:it'ct dispoziliuelor tu carp solirj, Er.lit. Acadr:rnili, I3trcurc;ti, 197{i.
!. l. 'l'anr:r.:. Zeilscir., f. Physik, 7G, 849 (1932).
F i'i. i. 'l'anrnr. .1. .lj. T. F-., 3,34 (i933);
l* 11. ,\. llchtier', Solid-Statc Cornnr., SE, 2i}9 (197ti).
,1. S. G. i)ar-ison. i. 1). Lc'r'iue, Surfacc slalcs, in Soliri Statc Pirysics,35, i (197{.)).
b 5. \a,. Shockle], l)hvs. Rer'. 56, 317 (i9:]S).
6. A. \Ian1.', Y. (ioidstein, N. R. (;rovcl', St:rnitonrltrtlor srrrfccc-s. Arnstcrdarn, \ot'th-I{olland
f

Pulri.. 1965.
7. D. Frankl, Illect.rical propertics of senticotttlLtclor surfaccs, Pergnnton Ploss, Ncrv York, 1967;
Ii:. I. Kiro\-., S. P.:\lexandrova, Phys. Stat. Sol. (n), /r!r,781 (1978).
iJ. Y. Nlugourinslii, Phys. Ilcv., li]9, 1910 (1963)
9. S. Wang, Solitl Slate Flleclronics, liccrarr-Hill, Ncrv Yorli, 1966
10. V. Dolocan. l. Bolili, I. Nazarenco, A. Vancu, Colocpittl nalional d: fi--ica;i leltnolollia mate-
riakior cristaline 1i ttrnorl'e, Iasi, 1980, p. 271.

11. D. C. Tsui, l{.D. Sturge, A. Kamgar, J. Allen, Jr. Phys. triev. Lctt.. zr0, 1667 (1978).
12. **T.*nM**ariPS:nru<or.gfratroec,sesJs-iPcnihesyntscrr.efaS(crocecva.isnJtdadpmlauennm,a4brd4ra),.n3c32sc(ie1n9c7c8.).
13.
14.

108

601

k'v) 'd - ^x: 6D

utfelo;r Flsrxa rry wayelr.t-r1t-;nauo;rg.ce1a ri 6b e.rr*ar ep ai.rrduo H?IsFF
lnJcnl oJ+uf

(r'r) YE+I :wX

ut{e1o.r ur;rd pqrur;ap o+sa uo{r1ntrf €Jtics uI uelrg.r,rrj,.t:5auo;r1ce1g .tg]

ii-u---uosu1oaoJgo{(+l.,cIurefIcc.I5_gona€ollcu-Traultr,oTr{upd.lu1nigloucofrg1seztJcull?eeloK1oce+y+coesatula?aoqro?plrcf.un'a?[llq,+6esroo€ldp]uJ+rop{rgi€auqdzroawO+(.t;aErfsil'zoc.otorra'?eczF€l1roeou+rl,usa+oioegusr8)""rT3tl,.leur"+cBro/qlcr,,p-.sufSuilFongra?+.d.Ipritf?uors]rz1rplsroornuasuaE1Jontllrne5nin.,ciurlo-er1aarqr"alrrpoonara:cupiergulrrs4"u5lrnoo1"ue;rg-utrar.or+ouceunupracrlc[sp)lr,o+r:@ulacJa?ItsnnIb1Jopi1iurIo:1lSirppcruialrn.rrouXo,mlrtr+err(',l1oltla]nizlrt1ur15danrcdc1aueirTrurar,arlrrI

IniroJ+cala ez€ozrJo+a€J€c o.rq?c alrrilr.rl3Trr o.r+Trrp u.rn1p5o1 olso €+ullslr,rJ+ur
truolqc"rd O'0 Xb nc Bzuo+ou os ri rno;i1aaia n,rnuad olt3+rurJ€ eliarrmu ar iri,rrlp
-uoc oll rrzuoq Inrururur ,l3I +r0n]rs u(jJlcclo un pI-\ uI o?tsors u n.rluad q?J,lrsdtou

j\cl ul o:lrso[oj irlr':jr:1ou ua crrlc.o^.rruc JoiJii]_\lrr uruu,r8e161 -.I.f .n-lC

__m^, *--- T
t- J
-- I

'foLrf'.7'An/7/,//-r'u ,lv,i xt_____
,ji^g [v3 t|

f a 1iI -

U 0i1il IC N C I trif S aJ I :i.r U:Sll tlj0lV

to.rlpSlo"lIorneruucrgnl pl'(rofal'€fi+rla'.oi4r1l1u)ror"crlpsD'purnlorcuDlr-uJuao+ncc-lJnT?pJuutsorscroruJu.orrouostsTrqFcl.lrrlo,eu*5at.reoglurs6oabIanntl*oco,trrFuzoup'ta3I+Ino+Juecnna?Tsrsar.rrroiaJrl
olurJolr?ru urp JolrrroJla*Jd l? a;rg-i;r1 op In.ranT .I.f

uoecooNocll\Tgs-Tyit $ru TfrJ,c\rilNoc

ft InlolIduS

unde P este un parametru de periodicitate a cd,rui valoa,re este dati in
tabela 4.1. fn tabela 4.2 sint prezentate valorile lui O dupd, relalia (4.2)

qi valorile experimentale, @""n, pentru diverse elemente. Cunoaqterea valorii

mIucertuallu-mi deetailerqyiiremeesttael-seesmeniclioanl5d,u[cato] rl.n realizarea qi utilizarea structurilor

Tabela 4.7
Yalorile parametmlui de pcriodicitate, P, pentru clementele chimice

Subgrupa P, eV Elemente

VIA 0,3 Sc, Tc
IB&IIB o,2
IA&VA 0,1 Cu, Ag, Au, Zn, Cd, Hg

IIA 0 Li, Na, I(, Rb, Cs, As, Sb'
IVA&IIB
-4,2 Bi
VB --{,3 Bc, Mg, Ca, Sr, Ba
-0,4 Si, Ge, Sn, Pb, Sc,
VIII V, Nb, Ta
--o,6 Fe, Co, Ni, Ru, Rh, Pd,
IVB&VIB
VIIB -o,7 Os, Is, Pt
-1,0
Ti, Zr, Hf, Cr, Mo, w

1\{n, Te, Re

Al, Ga, In, TI

ln solicl se consided, cd, electronii se miqcX liber in band.a de eonduclie in
intreg volumul pind, ia suprafata acestuia uncle existd, o barierS, de poten-
!ial, aga cum se reprezintS, de exemplu pentru rrn metal in figura 4.2. fn
realitate bariera d.e potenlial la suprafa.td, nu este rectangularS, ca in
figura 4.2, ci se rnodificd, datoritd, forlei imagine qi arat5, ca in figula 4.3.
Un electron a,flat la r de suprafala unui metal induce o
acesta. d.istanla sa,rcini,
pozitiv5, in forlH, de atraclie intre eleetron $i sarcina
Apare o
indusd, a c5,rei valoare este egald, cu forla de atraclie dintre electron qi o
pozitivd, egald, in cu sarcina
sarcind, distanla-r valoare absolutS, electronului, situ-

atd, la

zr q' q' {4.3)

L:-:-, 4ne6(2n)z L6n eonz

SUPRAFETE

mFicgta. l4s.e2.a-fli Electronii in tFiaigdl.ca4.c3e.itle-reetBrofanoruirelluraei aimmdoaegdpiinolietce.ant-i
intr-o groapi

de potenfial.

unde e0 este constanta d.ielectried a spaliului liber (vidului), 8,85 x 10-rz

F/m. Energia potenfial5, a unui eleetron aflat la distanla r de suprafala

110

TIT

s0'? g',V L,E g'0 i8'9 g.\I JZ
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a1to6[ | Ao .ttix Ae'y.? Aa'1 udn.rEqng | ,..-orn

l

prlos uJp

aJISeI ap InIuJnI eIB IS raqll lnlnluolB Jol.rlllsJralrBJec e.rdnsu olEp alaut]

a't DlaqDI

uretalului este ega15, cu lucrul necanic efec,tuat de elerctron prin deplasarca
sa cle la co kr, clistanla a.

rz(r, (*) : J|af --l'rlr - lf i4.4)
,

6rJ eo.t'

astfel cX llarierur, dc poteli:r,l a ek:ctronul'ni din rnetal aratii, ca in figura

4.3, unclc I/(r) se mt'rsoar5 de kl nivelul viclniui. Bariera de poterrliirl se

modificit, tlo ast'rnene:l, prin a,plictr,rea rrnui cimp electric in veciniltatea

tiig. .1.4. - -\licsorlrca irrirl-
firnii lllu'ierci clc potcnIial,

crr ,\(D. in prczcn'rlr cinrprilui

clccl.ric, tl, aplicat.

interfe!,ei ntctal-vicl, (r]. oEr (fig. 4.4), a,qlfel ci, errergi:l poten{,ialii tolrur,li a

ciectronului m:isuratr"l cle ia nivelul viclului cste

-^1-{O, (.") ._- ^2 + qt,tr. t1.5)
162 enr

'!eeast* are va,loalea, rnaximii,

ro - \{ -+llnro-\1/tz -,t8 r,, , i.+.{i)

la,

- :.r."" ( 't '1" (+.r /
.
\ lc;eoE f

-4- Ific;orarezr, l;arierr.i cle potenlial
gx)o
nrc:,1u$n0mA:6teVD$2/rit3n'em.ip"chlfes.ezecIe^ttonrb-Slf!ai'icgnhuceitom'qatAtpi4iOuy..liu:oPi ecc0snl,e3ttrcr9'utlr'eeicEpYl'(:sq:e-i
I
zentati, cliagrama de benzi de energie
tr la suprafala unui serniconductor de tip
p. Dupri currl s-4, ard,tat in capitolul 3
L"r <0 rlatoritil std,lilor do suprafafd, benzile in
apropierea srrprafelei sint inclinate. Pe
l_I t baza efectului Schottk-v, printr-o trr,-
il- tare adecvati, a suprafelei semicoriduc-
F sQ.'%
X> torului nir.elul vidului poate fi coborit
E
sub marginea inferioarit, a benzii de con-
cl:lilqe.rg.i1e.5.a- I)iagiar.na de benzi de
unui scrniconductor ln duclie ,si afinitatea pentru electroni szi
conrlitia cu afinita[c clectronicii de;r'inir, negativzi (fig. 4.ll b). Mai plecis,
pozitivir (n) si ncgativi (D). d.evine negativX afinitatea efectivri

7L2

LeLTLf OO9-J8

r-:rIu'ro,'Ju4?CI,;)Io(qIl?agI+n'7uJJa'ouleoago)dsan'flscl ul€erJqaotJlortsupqrl]ocBuJrll?r-s+runxIeSosaJ(oiolz+luecnozprqnudof,cuer.)ruuraqansor.pIu1Ilin'pIlsB€r+e?apsIIIquuefripl.sx - *eb:
cs r8o,aDu op r* ruo;r}colo uJ KII?K"r€s a+sa Jo+cnpuoaruas mp gier{uds
oa:r1 a.rur
oS.iaurnu

aunr5o.r Tls€a,l\r 'rrrlr?or{ ou,}{.rur?y.u4.rurdornos.rpts5ouqol poapp.rriog?,lcr;nrnpculourrrirnrpasf+u*lpp (?gurtDllJ)?sf"al+p
-izot{ pura.l,r3s o cir}urcJ es
eun"ilod o
-aILd{IO;reS1upr,plrlreu.8oJalu"JatulorcaJipasrnoln.ar?"rJusdir,,uB,gr?nlnil3lel+o,Bri+rInuziae,rg'rr;C;rdn'asl,cBrJIal+it,?tsloruruEunJoJpoo:}loitDllpIuro{p'l

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rzilJ{J.tp lure.ro.r:111 -.slr .3t.r

'ti!#**,^,12fq vllit,
"t tL,i-.an-"1f tpo- ';_:,--,l
l;"'
l _J _:"
UCif,nCNOJth:5 P!,r ln)in1N lyi:yq

a'l-Jco,Br[yti.pjaraJJSrp.rr01solpru,loIoooJillit.cI)millllrpruJura;l]o+nrJsl*rruast1rJra${]ao[.ururp,1lrpu1ur ri5_rrrruuraiJn.,c[rr,arru{:;rn[ponl,a{undlrsorJalorrr+1r,rcrErn3rt,il0rleuil,dnq(o'cr[tln*ri)qla-o)-aalar"uD'r4r,ru)rJrrrlp,rrUuqa,rr1i}aiUus]1,rrnl1no:lrrsc,qBa'poJ;oqlo1;.lr1roda,)rr:rr]1iru1,1r
>l.1irqrsoriir+I;un'Jrln'Jlplpr?no{ar.loidri:'rJl ls,turr.r)rosuoaslrCu-"Ir''l4'?csr}ouosoums^"'r'rinr(irDillunro,t}ri'lrllcotLsor,+r{pJ?uoooi,CaeJpl{aner({1iorucat,u?Ir1r1r.aur.scrclo.Jrlsa+ucurnaIipgo,uusrl.rlncJrulrmxt.rrjr.lcb.lrut!c.r}lupslr",prgI,n1rq,ru{uio1lr}uqoDoD;nziopaliU.raucOIllaCj?r.rritUspanrial}srrs;ri-r
q'9'7 'uln5rt u3 .rut 11a_u1uot uJ ?uIS..nu llulr ?, ct11 ap lolrnliu6orures rrLun ri
I'u'l3rrr inurr o1u
clr? acrlaF.raua olaruurFeip oin:lnazo.rrlal ?uls ,,g.1.. u.rlr.3iy u1

LDdpL Uzuc .Y

.rolonpuonr{rr.}!i-Iutaru Inln}ru}soa r: parll{ilaua nurrufir:r11 .2,.,

",qo1'lrn-pprltui.1utrs?oadqlisio]-u,?ctolrlstl-HzinlpJrrlrdB_lsgporupSsolro.oJr"or'du'll3qorgiuci,l,.Durr1r-0u1oJeI;rr3L+oaI;c+"urroraoIlcg+nt,ru?'upJ"rlua,l0rrcJrs,iaB*i+ltrndlr*Daprp*l.usra-ru.'errrarion+JlBsUn'arr.lrtru,u-n,0,i-il.;iJr,tilJliJjr,u;ol.turl;?.'r1edtran"i.psjl1n,!pi"irirui.r"rrori.u:ra:nrln,aj.;ip1r] 3
ul--lr1t3tluz1lr.ristLru:I-'r[uJr'or-uiEJt'-'o1quric]rall;'r)aed[i"]rpopgy(p_€tSDuaIcnco'rfpirIll).llcrrap.n+u'rc.gapoIlirnluJxantsolsddrpJoo'Balrurto/a;surupacrrrrh*.o')rep1rqr.erlz0Joru€61po.ra?.lprq8.'5"re1oe6:€pn,+u0glc,carngltnJtJ_'pl1rgul?uu'+ogooor.rarcJJ_do..aro]aJucpruararJiso,rl+ua,{.rraroctausolwoipr]i5iJsi,?,rporog€IelrrirurrourrurJ,{fgnuroa"sarr,rcosriruplipluorrlus.,rFr'rpaur,rnp:u,gi,Bulr'rin6.J,i{ioriornouq,id{r..frorrroi+aprl1iriJi1lielrlolooi",i6lrlo,J]rar,Jartitiiu'rlqraJIniprO1*itr:-*;Jir.i
(s'r-) t"qrb< E - "g (
ntu'olLaJJauootzrlr5rBz,.tur]u!ro)ru{li{c)rJrqriErrJnl+t?rlunuIrSrprl]crn1u^ul"lIrnaoFlluoraiz}rarluiJJurooouaq?suaroproJps+a'uqus!nr1'pg)rr{'u!tbr|rr{unuur15auloon;o,rru54a. r.guDJFrlpDpaolicorueclorren.iplrc,?luulncueapo(slugaqco_>olro/+u'axorospbil,ri1ulrruiuruzJnlour,cauo.rrqul;auasra-up,}ppa(frraeur1,1oniur'r1uip,lqruiueduao}rouicg"srri

narea este cu atit mai puternici cu cit diferenla clintre lucrrrrile de iegire
din cele dou5, materiale este mai mare. Pentru o anumitd, inclinare abenzilor
dcs/fleeet?voeilnlrneldienecrevgleiinnetiepd-mipna.EiAs, mep{maarr0ieceo;adinsedctfacuelcltatiotnnar:rvepeelcnnioineadpcr,opteara[lt(iseJuta?dn,ec-roedngEitniauocnv)tefeutcllI?ui]nidq:u',ihtnasetsemetarixaccpoton[tn(lteEltua,iccn*ttovujre?luur)I-ii
siune a tipului d.e cond.ucfie. ln aceasti situa{ie stratul de baraj este for-
mat clintr-un strat de inversiune gi un strat de epuizare (fig. 4.6c).

In figura 4.7 a s\nt diagrarneletenergeti'cJale nnui metal
,qi unui semiconductor cu"e@p,"u)reOni,anteesituate in contact, iar ln fig'ura 4.70

tr E,
F
tr
Ei a

C

C

-F'ig''1'7' Dia#'tt ;,TT"i;':"i,i"6f ?rui. nretar-scmi-

este I^nreparceezsetnetaatzS,dedo.iaargercaemOa .e{neOrg"ertiicnXparocceosnutladcetuslutai brnileirteal-aseemchiciolibnrduulcu-i

tor.
'vlianorvererdtsreercyeielleacmteraocihnmiiliibaunrltibiteeenrlzmeicleictrcoilneniesndeeminrgicireonnedctiluancl stioenrmsviceaomnaidpcuaocrnetoduruncvtoosrrtrfadi t.lendcc.ietlianincautesmeunins-
jos (fig. 4.7b). Pentru contactul metal-semiconductor de tip p pot apare
urm5,toarele situalii. Pentru Q^ 1(D" apare strat d.e epuizare (fig. a.8b)
cc)in. Pd enntr-u E, > 0 apare strat de inversiune a tipului de conduclie (fig.
'4ia.8r O. Ou apare strat cle acumulare cie goiuri (fig. a.9). Pentru
)

,'hrrlT{- "a-- lt _E: ttcr
Ho*'e.
| *,,"" .'+/kl-|-r--7---7v7 ctrt LEl.
e
" F

F

cFaigzu. l4.(8D. -- Diagrama energetici a contactului metal-semiconductor de tip p ln
materialelc sint separatc ; D- strat de sdrdcire; c -
< @, : a - de inversiune. strat

t:

C. Ec
C.
E
F
r
t:

aFi-gc.e4le.9.d-ouiCmonattaecritaullemselntatl-sseepmaircaoten;duDct-osrtradte tip p in cazul (p.)$"

de acumulare de goluri

.L74

9TT

{rrp) ,nNznb _ (ap-)

(rclr)p

eu1{qo as erso"rdxo €rur?In uICl

(gw) ' ( (n e--rn1,t.)rz-J\ ;p: Agltts : c
/r(

{crp) '"nL(A-'A) nN.o6f :pngb: b

_rale'lrcudec elgse"rdxg a_p oB+u€rpor+€usis'0oTrrt's} or.prn8r?roy+u€1gmpnlegoudezfae""rrdu6q.ro-pe1rnsoln'e+i.uez4i.sr

I3 0 pler{rcrs
-eiod op g{lpuga osroaTp uI ro+cnpuociuas-I€+ou rninlc€luoc ts ei8"roue op
/ -Izulq ap eure.r8rlc '?stsru gI +uFe1 gJaplsuoo os or€c .ln"roq.cnpuoclures n-c
lrode.r uI rsJaaur a.ruz1"ru1od €I snmtu lnuruos
I nurrros orv A opun An nc elSeinaoius os rosrtpelc.rae;zrrrp.reolo.rdene.rp-er1ro{1dpuu1ocsnrlidl

{rm) fAepbz) : b : n)g :'ug

(sm) "nF

'rn(Nbf,Lez) : F

-(+-.')+{am) 'oA : @)A

{rrp) 33 - ug : (n - P) rrrb- : l(r)c I

'* rnr

'u d.rq ap : our{qo eg
Jo+cnpuocrruos-I€}oru In+c€+uoa €Joprsuoc os 'Jo+onpuooruros urp
roFJouop ur{.e.4uoouoc o+sa a1g 1* tu.req ep in1n1e.r1s uaun8.rpl olsa p opun

'o: (p),! 'o: # :,p *

(om)

,oA : (0)t :ruts #- :,O n

K+Iiil{ e1 g{rpuoo olor€o+?uun nc

to .- r 'ol
Ie{.t'r)
t'-{r _bst l) c r8 2fr0
'pln>o
se Az0

uossrod er{enco tsqozoJ as ro €aurr Flg rS rarorrtsq reu4,i1pq IsgF €

dc uncle se cletermind, __2 _(_-_d_v1 \

-\'ro -- ,tu d(Il}'z) (4.18)

B. Cu,zu,l rea'I

in figrrrile^4.6:4.9 s-a,prezentat cazul ideai al contactului metal-
;rsriecmtailc-soenmcliuclotonrc.luicntorreaselitamteodtliifaicgiriaamtait cle benzi de energie a contastului
tlatoriti,
efectului Schottk-v cit li

Semiconductor n Se.miconductor p

,T- {n
eQ.r t_I
Cr.po-Ii r'll" _=-- ErF"
I -^-^ffiT

-7/ /,-/,/

t!$v ) F

E Irig. .1.10. - I)iagranra cle
LreDzi cle ('ncrgio a ccntac-
trriui nrctal-stinitottductor
irr prczcnla ritl".riior dc

suprafaJ i.

V)

LEC

F

c

cla{orilI slr'rrilur' {1e li} slrprlrfir,{rt sctnicondtrclonilui ('a,l'e vinc iil eontnat
cr metalul. ln cazll clnd*exisi:"r o d-ensitate male cie stii,ri de suprafa!5,
inillirnea barierei d.e-poten{ial gVu poate s[ fie inclependent[ ile lucrul
r1e ieqire din metal. In figula -1.11o sint reprezentate benzile d.e energie
irreta,lului ryi semieond.uctorului cind cele dou5, materiale sint separate.
ale aceastil situalie benzile de energie d"in semiconductorul-
.ln tip r pinj
fn
inclinate in sus, deoarece s-a stabilit un e:,hilibru intre std,rile de suprafald
qi volumul semisond.uctoruini; to_ate stXrile de suprafa"td, cle sub nivelul
ilermi sint ocupate cu electroni. Clnd se realizeazd, contactul metal-semi-
conductor are foc schim'b de electroni intre cele dou:i materiale; la supra-
fa!a, rneta,trului r-a apare o sarcinl negatiyd, care.cregte_pinfl cind" nil.elul
Fermi se afl5, la acei-aqi nivel energetic in intreg sistemul, adicX se atinge
starea de echiiibru termic. Dac5, densitatea st5,ri de suprafa!5, este
.sufiaient d.e mare, astfel inclt in procesul tle stabilire a echilibrului trans-

116

LTT

_",":40'pp ATl,

rrso.rctrxo ap E+rp a+sa 1g g'ftge;rdns op lr!']r' op [:rl]ca]a 'eaxti+rsuo6

(oa'r) *EoA t" : ot\ : t"O

''"& nc Jo?snpuoclrrIJs t-:;) !lJ{i'l a?B?
}{jriLllllJH.rl'.Ii]}l]Iii'is'id:ri.' }rJ.il.tlni.lrltJ?Fs+oirprr[nii?'E'qJ1?tsz
-rltsJ'lnau op ur:ilpuO3 oc{ eulalu,s ,I'BI ""{l n'!
rrlp oIJtr ap uolulrrrrl
-rltsool or,ra op €o?'u+run od tiulc;ttls fzuolori ;S 'Ii'.1 r3-1e;'e.rci-ils il1-l .loii.lSis_i1i
-g1rsruap r: e1.8;reuo cp ,ecilorluJucI nus glurirituotlxa trirropn*dop o pulilncln::
-a,rd aui{cyt as p,lr:gurclns op air.rF+s o.{1 fa op ri}JolJerq lrlHtr}rpour- 'u 'llli.rdJlp
orse;rdxa 6 '(a1'rrurlru,r +tiTS nu orF.roua ap al?s e[rzuii(t rlap r"l ,ro]cnl]uo!lr{11-s uE
qsnpur gur{,tlctrs uurcl't:s F+srra rin prrlo) q1e1ci q'nuucl oI} nJ,Gr]JoourJrtu?.qreuc'l.iirirtii{1oe]suar
ap a*lGtr,rl!. u;i lurclo.rdt o+.itcJ'ltaivlsnlu
eliainnu os ri a{.;
*@ 'a-IS/alg.TZ 1r'rrui]?srr-'n.itTrct{ yqf op Ei}.rut}Iua ne E;r.4chuelrt.l\ 'i.:lrr'tr}q
";{uaiLlrttt '^?+u.rt? tlo.ut,rJl Ii}lrll}{tr- apun
-Coc rr'ai.so-ln--i lrltE'ra.rdrii; lrp ;rcpjgit

(arr) 'i'-",r1FI 0-r(--r-rr= -l

W I

J-'rtir-o

' utt{JoJ op psndo.rrX xsoi 'll yitl;1tl.rdns op ilrJg}>-
-rnu*.drrl.iuur1oa+ict'oAlu-qpaI.yrguglsJ0ryi'Ii0Ilrl',:"r'io)+r1F;I,1;n)VAIJ,orO,Lnlr)?rrCi,rqr^lltporu'Ul'rLaOirsrJrlr.J'Lrnl-loinlIcolrirSc1li--"iIl'gLJlTr1,ilal.,ulrattoJ1ittillitqiipk+ul;rrlrlt1l];ilrll,uituJ-{1,n}'-ttlrrun1rir.-I'rrllllur,-rtlalf[,ri]'ll1lus(rrJ'].Eql.+Ilt(ls9ls\rJfri'i::lOil,ltlltasasriJa'uga.t
,il:)t.;oilt?p rJ.{;}I.r,uq, ila.ru.roiatlq 'rttTn.To+tnilrlo.}illrilti ru F-u}EI.r.r tlal'tltr'rtlrturorl
rrip "'g tlII].'llRI lndrut'l no
*1io "" oliun r*o ' ''3 n; 0a JuI [e.ru<1 o1i in+t,l1i'

'(.r) ]u+l>rl,r' rili;:dtti1:r tlinqtllstp : (q)
'.;r-r11:zLrltis;r.ittr h:dop t;t ytr1r.1o.rd : (D) 'c!I
-L:lJtt: illlJrrl'l,r \ n;t:l- illlllt(,l.rlrput).)lLLrJS
u irllJltptro:l .rp rnyneirl l1!ii.rJ.\rroJ 30J ilJll ';trtb-u{iii r.,..i.rt:.t itr]lil];i J.Iu.I.)plsuot lli eJ
r,r JnzrJ:i r-r1 .ti>i11or1tg t?.t.)r.tB{f n.tluod;r13 .}l r'rirJ.ro}Jltlluo.llrtiiis-11.}Jtrl iililrlJi:lr1o.) ll
-JJur itp. r:.tr.rq ill] ururrriur6l-'eI'lt '!ii.'I .rlii.if,ii;) Jp tzu.)([ ;p t;ttll.r.li.u11f i! t"iilil

a1!arn,lo1u; as (9'?) 'ulsa.rdxa ulp E inl BdJ''ao['i],! 'uT.'{- u.rn-ErJ ur ts? !]'r--i'u Jo}
-ltlpuoclulos-I'l]loru 'porla$loua 'urue.r5trlr ii (g'f) tlD'a,Ii{xa ilp
Inln+cts?uot u

agp1tlr-raa.tr's(aoqri{ut4tc'1fl1.,ur':aSqirucgrg)riIllnupFuiagr,i}nrc.:ouuJnrap1t]ra.},(In,Jr*ooeq+roEonppp1uItorru'cirrtrrnauo1l soacpuI3lKppluIo1+.1iI)1aouJIr,'u1l,tltc?lJlstltluar-uJrrancpJuiu-rsp']rq{iIr{rlaISiouacs{

,ule+caJs olJ 'lis B.rT,J m{egt"rdns cp alr.r'F}s etl a1: }oI Tqru IS luo.r}oil1a rrp l{l.ra;

raetalPurlesseuppuonaitneclscedr,ieto8a-Ft'e: st5,rile de suprafafd, sint in eehilibnr ;i cu
deci
- 8{D qi

{-:\-:-d0q'd"o' t+.2u

Se considerd, o distribulie a st[rilor c1e suprafa!,X de forrna {+.22)
{.1.23)
0," : 0r [exp(- q(O - O*)/.Eo) - 1],

unde .Do este o energie caracteristicir, definit[, prin rela_tia

# :% Eatr,

peQes7tesetsdctl,eerinlsesaitdracetiensaau, fpairxpafafar(elaEntidmin, pdcueornitsfi,itgliituroirradliicoansdiuzepartbaeaf)ancldiard,repinieactadhc,ieli(barrspetd:a,zci@,ons*)faigr$cuiirnQaa1l,/iDdeeo.

Prin urmale

: # -qr\r ""n t-q(s d,*)iEol {4.21)

q{Oi nontuinecsl teErd:efiQnirti.,peeontsreu 0,, ( - Qr). Determininrl tD clin relalia (1.22)

obline

(D:(D*; Eo r,.I[ 6t l. ({.25)
E-*.,
q J

Aceast5 relalie conline trei parametrii O'F, Eo ryi 6y ajustalrili, in
comparalia teoriei cu experienla
pentru diod.ele Schottky. fn deducelea
ei s-a neglijat efectul forlei imagine (Schott$'). Un alt model propus ia
in considerare mod.ificarea profilului dopajului qi conversia tipului ,rerni-
conductorului lingi contactul cu metalul (fig. a.13). Cimpul electric nraxirn
E* in stratul de sarcinX spalialf este dat de expresia

U*:fr* Q(I-u * iI") dr {4.26)

-s "0

unde lV, este concentralia impuritd,filor aaccceeapsttoaadrein$ui r-mlfd-, concentralia

impurit5,lilor d.onoare d.in semiconductor, fiind conside-
rat5, constantd. n* este iocaiizarea maximuiui energiei potenliale qi n3 este
localizarea joncliunii metaiurgice (acolo unde concentraliile celor rlouX
tipuri de impurit5,fi sint egale). Indl!,imea aparent5, a barierei este d.ati, cle

expresia

@o: Oo * n(t(N, - .llu) dr (4.27)
\:r- "s'o

,si

d@,
dE^ - ^- *tn'

lIB

6TT

,TCT
)'*w:*'"d+ -Gz'v) "apf,ap'ap
( (a -'s) - *(Za 2a

wp @) { (s)"6 - (2a t n61 ,'a) up opun

6--6-2*Qa.

(sz'r) J_!_\tlza tna Pa) up *a b-:*t{

ttl op K+€p o+so lu+aru ul ro?

-cnpuocFrros ulp co.rq or€c luoJ+cala op luoJnc op r3o+€+Isuaq 'oug8uun ia{.rog

Ir'gnes+uc€4ofcJipoluouSJz+u(sqeuf)lKlF:cnoru?rusasalrpu(co)+ruIrotoqr+oqrJ+su,raaprlsoolarru€ofurr.+rrceIEeq1ruoo+ptIanmrtarrl1n1o+t+gss.ro.+rd1suu4r€{uto['p4lo5rduaeuaup4psrolor"roraFdrru(auqs)

: rreundnsa.rd e1a.reo1gur.m u[ ocnpop os crJ+colo rnln+uoJnc qsa.rdxg

0c!,uottcal0o1il,J0? xaxsx'uq nlJoaa'Y

l-'-p*rq?ioen[ouyfp]en.a+rodloToncrJsr€gJoropo+puporlJz.srol{drlIrono.rocIgz+FnusSJI rIF€piuacaJqu'iI€anrJoouOgcroauou?+s;rsoO6r.i+1oruS9p1cO]u€Crre{o€Iuuree€rz.'SrI1neo'lqB'ld[poZO-zUarlA'pogoIlIs€]cIJlJluJngot.a1lrOrec'Ce1toqrlOuopInuoAlurrC..uorrcerulorluoI+e;arrFoJr+agAIruJo€sao-rrJJ4uu+luUaoclrolOJqlIooTlAJaJo€ogOoaoN??oJ
-I--ociqfJ'c€a?uulsoto€sifnfu+lornsspqol-xeeufJadirJxq'lnggocfs"'Ioer1etusnpn?1xI.eorroo.rrdducslslruurrr(.o;rrrl1era"qru€oin.1IroppJ1fuuo.ruIqncr.iK[crnJprp.crouoecolongctpqriou;1rplnsiedsor-ls{luuucd+eIrosJc?aruucroI,onrIoclIrolJrJnun+;loncppn+rd.urrt+nocstrlun"ur-cudftTuaKcyuctItn?r

i411oqog Bpolp nJ olrlcala [n]uorn3 't't

I

-:'pt..rrsoerlyc)onAcpluuul o1acr-uJzruqr.0ru:sls-olrdEulJxcJarul- J : eltJiln cJuz
nI.nIqlnllrlqccBol.rirllo-J
D

e
.rrF.r.ru.l Jp rzrrJq .ll) l,'ruuJi,utO - ',.I i '.cljl

r'ercar+gscilrxae?c,rrlo3cJIuainlunf0u;doBpII€inmlnopultosJ'c;ol qu,'pedu;4ruuqnc1rppop;q'eoo"rgiu5urBi.rru1agdl.cnup?I{qutysuua.plrcpolnasoruuanopl,srouuIaIJr+nK-+cl.srrpa?drInn?cYp

rillde gc(A) csle densitatcrt ile stiari rle ent'rgie in Lranda de condrti f ie, ro,.
n:inimii pe caJle trebuie s-o rriltii eltlctt'onii
c-lilevtirtelirizl :ii,, j]olrtt'u ir, esc:lla,rl.r, J:a,liela de ptilcntiai ce se cleplast'azii ru

ta.:( 2q(l'u l-) .11 i {.u(l}
I
'ft1 ,t

Se oJrfine

: rl'l ?:e:rp(- qrir,rrl'?') eril(g I'11:?'). I ,1.ii1)

ttttrLt,-iti -- 1;'tt-i'tLttr ,^ t'2 r t?lnt,s{(, I!rll.iilcfr,'iiri'lt,r,lo('l11)nilut',/, - ('r)ii:1i,illil,

It3
Il:uibiel2Ri:Ooi,l,fAzi'ul/'cuem-sr,tzterinIir.:soiinnsf t,ei-lrn:tuat*e!tl,nuialirc(I1ll.ai1c1t&r1iat)':lct,,ilsi*rnorcrgsltaac,,ttclleirruiIsr{sieetiltrit-tctin:lre,. ciEntl.oii'lchtiracz,erndlsineonlrtr-,ii,rlfrlr.'.rri,:i,ti1iivloi:r,l
o strlilafa!,il l,-r -lrqrsemzei(nroluncteluri:ltiolrttiiiuliicicuu, o olicntate rlit,tir. \rtrlot'il',,:rrtltr
;itne*r'-t,il1ugf i1 r'ri,zuli sin1.
1.3.

ll-ubclct, ].,1

\:alolilc r::rporIir iu i ,'l*,'- l

Sclriiconr.lue tot' (.i c Si (ie:\s

tip ,'r, < 111 >- trll .) ,) 0,068(cinrp slnbl
iip ir, < 100 > 1 10
2,i 1,2 (cirnp in-
tii:,t-,
0,34 0,06 tcils)

0 .62

ir:r, e{ri}iliir'nr 'lclJnic c,urcntr-ri ciLrLr cllr'ge din selnicoitdut{.ot itr irrttir'l
ers{e eg;rl ou ctlre}}tul s;11'g 1lrr-r'ge clin rnctit,l in. sc,inicrlndrtttr,r'si:},r'c t-ulol.t i'eri,

.lsr, : A'* 1-., e-r1i i- r|wt,1i;?). , I tD\

,\.ceilsl,tl ('Fte \ ibloiircir, ctrren1il1ui ca,r'o tlei:t' clitl rnctill in seinirontiritiol' ;i
tinrcp.jredzinennlalrttiiinleini tesnesrniuicnoinad'prriicctroa,tt'ei],11d{-srsoi'tJl'leo{dreifiTc?rr-.:r.r.iePlalilnicrul1l'ruul.i,re'Ller,ccrtleronnsijlirlcttz:lare,

culrentului net rler electroni in preael!,:t 'retrciunii iiplicziie estc-.

j ='- i,n, *- i,,, - .jsr v4v,hr - j,., -..i.*7 {t,rl-,Ar -. 11. i-J.,).)/

P"elilfi* (+.33i €rs1,e a,ua,iog'ii, cr l'elit,lia crrrcnt--terlsiurrt: iu joncriiultil y;-ii

cu rleoscbire:x cir cru'entui dc stltura,hic, jsr., :t,I't-r o exprcsie clifelitri.

Tl. fectri.a di.fttziei

ll-eoria di{tzieii se ltrzeirzli pc ulnl5to&reie presupu.ncri : (a) inilllimea,

L.m'ierei e,ctc il]ult tilai mare eleclt h?; fb) sc ill,u in considerare ct'*c1,ole

124

rzt

oP *,nu-o'r\

(atdbl { 1-)ort6b -t

ap{.r11 op

+ - :rtqtt,..r-,1,,)nt

t*n "r,o,nu-"'S
'.,) .r,t q.ia-Jnu

0 : r n.rlirod 'E+Inzar (gg'l) X+]IIIII rg oFrirpuor orrlr]-r ul prr[-\]i

'( -t0"-b : (r'). ) - ttt),)

;cp,.q7111.1r-C \
)ru l

1-:p /, 1tl /l' ":l .ur r1l,l|.t"1,r:il1 r.t{t,}

(f b .trp
t, :
.../-. -r ;) ;)i\

aurjclo os ti (gi;'-p) ug aro..r"rdr.r lrif.rriJJu ,)ltIllo.iiur ilr{

(,te't) 14lrtt.,t'\,) - ('r ;i'

,ilur.ro.[ ol) rI Jr^ (0 =.. f r.lli.iJc[)

JtaanurIainta8JnoOcm+aCo€nropaJUr{€OuanCl.olIazu,aIto3.nrl{'rnInl1,u4oIugnIoo'.d-r4o''lpa1r1JuuIatIs)r1+JdsOuuIoTuLooIrO+uJrrT:ritI'rs,):uonlaui)+,rt,?u-I-p4oB.},.1orluu.uro..)rluz((rIlt}uJ}lzncriljxr:l-inr tir0,rr=rti;:r{rg,5,UDo'1r"nr,)}I

(ce'r') 't : @)itfi tay : (p)u,
tio,l - o.7') b - : :(O)rtD ! j,,11t.1n_a.',tt (6)re

: XIIuII 11 nfrpuo,t J[.)Jr](]IlSrun tl,] r,r:!le]Zo.r or- i].rui]

:(se'r) -g-bf nl? -,rfn.:"i * ,rp
-l,p
tp

n*r'itn.lo auriqo as g(j,:1t'b) : ri 1S "+:pl(r)1p lluxnlrrsqns

(rs'r) . Ltf_ru-pp g r gn(r)r l- : l

rlb

o+so arJ1cala rnln+uaJnc ulsalclri,| zu.)
:tsa;€ rrX '1u;euasapau a+sa Imo+cnpuocruras (p) ,n"rqnlqra op rI*ol0a:l{rorlts,rx:l
n€ gcrpu 'c1.r1ro1a Tnln+uo,nlD ua.roca;t1 ap olu+coJ€ou ?urs ? n
JoIIrroJ+coIo apr{u.iluacuoa (c) i fe.r,ec1 ap In+€J+s ur Jolruor+co1a rilarli1.rclul1

Iltilizincl expresia (1.12) pentrp It(r) ryi efectgind integrala de la'

nnmitorul expre-qiei d"e rnai sus se obline

-j (-1rl2 exp(qV lkT\ - 7
e"nI -2rt{WIV-,, ;-)- T-) I
"'n
qV,1k,T)

r

sus se tr)eoarece qVr*ItT, exponen-tiaia de ia numitorul e\presiei t91.ir*e*c3tf,i.
neglijeazS,
la polariz:r,l'e invers5, qi la teusiuni rnici Ia polalizare

Rezult5

j:j"tt(eot"''lr-1)r i4.38)

yr. t''r1/2

J."n: jI
q2DT"f S;iv*,rq( ?-, -V)

=

L

se observ*, cir, in teoria clifuziei r.lrrrent,ul electrie (4.3E) :i,re inprinripiu
tcteeinnnsdsiuiiunnneeuaalia,ia'mppliuclilactcaXatzic',acl'nlolrei cinnatuzculalizntuveleoerrsrinediiseideisifautetzurimreaicliiee"rlrer.c,jttrrr*icri'eagzs.ctd.<u'i
o dependenfd, de
tleosebirea cir, pc

inclependent c1e
cU t6nsiunea inversS, dupi, Iegea Tru2. Este util si facem aici o compa,ralie
intre domeniile ile aplicairilrtat,e ale teoriei clifuziei ryi emisiei termoelectro-
nice. Expresia (a.3at a curentului eiecl,ric este valabil:i Ia cimp^uri electlice
strabe, cincl energia pe care o cirstig5, electronnl in cimpui e-lectric E parglt'g-iry]
td:r'roul2omYsuirnlldl,lipbreeeznrntrmltuil',i6jlpovecanilutolual,reaeapsiticceiarrnbnpiuliutlaltutmei ar*nitaenxorimirciciiid, didniefuscztiitreali,t:uTcloanc,ldetli-ttclitaailrqa,9j.l<6,h,,T:.

tt > ZQV, t. {+.39}

hI

Curn d * o'o'' rezult[, cX teol'ia clifuziei cste_ aplicabil[ pentrri "<litbmei-r
concentuatio
conductorii cu mici :t, purtitorilor c1e sa,rcinX qi drunl
mijiociu al electronilor mic, adic5, nrobilitate mici. Dc ercmplrr, teoria
difuziei se aplicri, la, retlresorii cu oxitl cle cuprtt iar teoria emisiei ternroelec-
trice la rediesorii cu gernaniu. Tot treea ce s-a, plezcnl,at pinri, air:i este
rralabil qi in cz-lzul contactului ureta,l- semicont'luctor de tip p cu cleoseltirea
c;it*tt(Ud)iacrue1rc(ud)p:,'Iitaat.in relalia (4.36) inlocuie;tr: l(0)
cn U se inlocuie$te se
p(0) :'1)oeevbthr
cu

C. Alte ltu,ncte cle aeclet'e
Iiezultatele expet'imenta,lc aratii' cX, pentru multe strr-rcturi lnetal-

semieonductor este ialalrili, relalia emisiei termoelectronice moclificat5',
si anume la ternperatlrra ?'a joncliunii se ada'ug5, o temperaturi fo

j - A* T2 exp[ -g(D,llt(T t ?o)] [exp(gV lk(T + f0)) - 1]. (+,40)
Aceasta se nume;te anomalia ?o[9]. fn rnulte ba,riere Schottky, ?o c1e-

pinde de polarizaie la o ternpelatur[, constanti ryi este ind.ep_enc]9.nti r-rumai
de temperaturil la crrrent constant. S-a sugerat cX anomalia ?o se clato-

122

l

E?,7

Ae-o'AJoogoelu*lsd(rOqg'xuotiog6ST+Veqsg:opuu0J/ogOlnrulrBprenr1)uodutqarg1ccA{lrIuoairdrrIS.rorongolulr(lugmralc"acaOllaptrsJu$o€roslorslcJ+rirogn'gtIl€+r1grAsJ1*n"u''nidlglnuErleuu>ozolafrocq€.rg[c4oAup'nO[mIOe9nc-f]s{gaIS'ntn0iUzun€'aZ8zcr/r-+.;IruuS4eoI/dnct]x40SuauJ.lerunZUdcaIItAr€r{ua{arrlau{J6oo1aruat'dg,€?r
0o,ugIrgJ{:eeK,rlSguledouErrnJoIouItcoeaqJga,nir'I0"Ir4ugauq.saquuc1ola{ntl€u,c,rtol"niacp.rcrgtnro.qucrefc'dqtulg(eno4r.;orlge*3c+urst€.uartcrlgouJr€'lJ1rSudKousc1'oo(s(ulungoqoAco+'rs:l+)o lurfua1oclep tlJarJtsq

tli{unca) 5ufg alsa

J ep luapuadepm

tr. n"rluad oca.T€oo6l

0*'r) *gltgt t Eurp
ug opD

'S+Inza.r opp{ugny,soupe'p(gua'Ba)lFt.rrfaeuiaa.repopolFuliti?rrllaiut?ood.rrlalollrl,a! fau.arupuKo.tcillloJupqltglzi'te?g'ul ;urcI{ns op

JoIirF+s

(grr) I uI p (f - tt)a 'rp gp
op I gp op otrrt

arrrrap (ff'f) rrr.'ienr,: ri

(sri) ',,,1"(r - r.) r'=*-lJ : s

purncop,r ouiiqo as (fl'l) erfula,r irrg ''giuye.rilns ap oilrllis c1'il n1-u,;"r.;!r7p.oiult.r qaI6

rnl tsoJ€oltsa alsd o In[ tsdJr]oltr.\ r:J J.trl)J.\ oI lllrI.\u ((p' li.r :4r irnJolrrr rr-.1

Gvv) t-p b

op - otr:l !11nrcr {ll't}

a.IApArl UI pulru gS ,1 nc qrodu"r uI (gf'f) ti (at'f ) api'iqa"r pullrraq

{err) :'U" (tfo y*a[t)u1

ouriqo as blgr14
( Y:'ua1 nrquod Fc laJ?sl3 '"Nbl"E
:'rnlruo+cnpuocrruos Inmnloa urp
ledop oarpl)aurrlfrt"trstzuoa+crru!org'Jaue+esuora0sgr ap (r-u131o16

',g

'(,-rtrl'rtr)ur
n{1,kv't) -,"

tu?+o1['onln * T : 1r ?,rptrtl

(rp'r) , ilTo (on * a)ry tp

b b Jrrlp

1ol.rcs equod es b[7,t1( n.rg.uea '[gi p'iu;;re'1ru ep
A*ITr,l?+s op 11fg11suap u er8reuo ep eleriuouodxe re{uepuadap uzuq od

ficr?slro+ctsrtsc tsur"ro; Xucile{xe t-s r* gfuo;ropo+uJ op JoITJK+s te{uazo;rd vzv,"r

pi cleci valori mici aie lui fo ia o tempcraturl datii, qi

g c1O Lr_ *- 8,,

dg 6-F8t EJ

eci:ec,euiaia*lei&*ep(ii4ni."s2*e3fm)llnrpueelanaztll'reuCiunelxbapaclilecesaftroecaaarztaesneronmmicnaiitf,liiee*ai t?b:iocenifrzizriliocoirri:,ic' deLe_-nsietmunaeo!ld'riegeileep;srtJeo?pomucosical-etctardlu'eel
rclogndrliuficcthomriit-rpi;roiniiiualpurioptlioriien:ijuciouni t;aictcuolunir-ceursrineei'ttiaplrurlluli9dl.e-Iru'cr:lrdcuecals.itc:i a, serri-
silna{ie

in5,ilimea barierei ilc fotcnf ial este clati, d<r lela,lia (':.27). Consirlelinil

ril"(r) = t, {f )', i,1 .4E )

se l.roate sclie in e'iotneniul ,i,,,, { $ <1 .t:i

_ 6t" dO, _ Q -\,r .12i [f _ :,--l' {1.4e i
cl8,o g..eo L ,t j

.\r'irrcl in vedele tlefinilia (it.46) a lui ?o I'ezultil cri irr ace;t cz-tz ctntlilitt'
g[,siti, inttrelpenttent de ?, ltl curent ct,l]stant'
experimc'ntaL ea'fn sii, fie
fs1n irrdeflinit5, de (-1.49) cincl 4:t:,,, ;r:i. Energia calacteristicil -Uo cste rlatir,
de relalia
n - qlggl
i +.50)

€, eo

Aceasf*, reialie a fost ob!,inutil prestLpunind profilni tlop_ajLrlr-li dat
ecuafia (4.1S) I lrentru alt profil, -Dn at:e altil exprr:sie ;i cste rle iqtgptat
cle tle rnc'.toda fle plepalare a
valoarea, Iui'sri^clepinclL ba,rierei $chr.rtt1iy.
ca
Cinrl -Dn>/i? nu esi,c posibil s5, se distingi nurn:ti din iuiisuraltil c&tac-
teesrteisptirceitirxftn-tlei,r'ecnlat ciini, efectul profilului rlopa,jului sllu al stririlor de sulrlatalit,
deterrninarea anotnii,iit'i 70. In afarii de t'fectelc sLrtdiate,
ilnportant in barierele snblili (curtl st'niconductcirul este. pulr:ryig
un rbl lritrelezc eiectrotri
il are tunelarca electr.rniioi. Iloi si tlc l:l nivelul
clopat) numeqte cur{rnt tunel sau c-itctroni
Feilni ,li atunci ctrentul eleolric sc niveh.rjui Fernti (f-ig. a.fa). tn-dl,irnui
n"uol"n"eg$"tiei*"cudereil$nutllld':re, etnisit' terlnoelt:ctronicii-tunrrlar*'
excitati'pe niveie
eaz cru'entul se

r

"E////-/lli,

!

--1 iu

iFniigr-.o,1.jtor4n.c-lfi.ulinlrc.ernntcutaI l-hsrelrnr:rlic(ol)n;di uccto[rrenptuullctr]t:lic,';rdisoipcatterIatnoprr-trllacrciIzi'aortrcitilr-iti';."retrcetliar l'(crr)(:.'';
la polarizare inlrcrsi (b).

r24

9AI

ri{?-'too,rpJuurr1Ioarurun1nulTgs,rzu-udea.ralao.S-rr]rtuolre'apiaranu(dscolrrtfsto,€tJrrl1aoqalsps;{1aJasacuu}sncrguF'(zra(€'g.EJrgJoF'tp-rc.i1)rlo+ttus]urlTopiiSuStnrdcl's{?a1u,)+olTecoIrqEgxcaptslp.rrIcu€FlBpaaooc11pnpa:]lrpntscJl+oEsurnlaJ{.rrq+d'puolpratc+"dlr€euzFrnepouppt
pp.rufi op laul na '(4ttoqas BpoIO 't'f

'Ju;xu11c{.r 1u.r1s ru ,t-11 'q l-i' '5ljl +rcop rDr.r r€Lr.r s,, Tfit"Tttt"lt"-,li.l
-:ioqrS l.rporll r lli.r;ur'r .rp umur8ul6 - uriqo as u-ls-ny rJn:lcriJls n.rlrrad

x zy tx a

(cq'r) "r.

rp {r)'ctrb'-"-\

J -__---_ uiula.r oBpo+Jru3cpoa1slsaeprJltn+dr.rruoiu;,rr'uf.rqonluooul
-ppncl

a,t, qY.l ' -ri's."r"u,\c p;l'p.'-r'"xr:-u'' lrcla r"a"--u--n:..r8a-"r u-;J '.-roFt..-I
- rtlr'S t;JruJo.ls col rJSl€uldriuc olr;.tlplseu1u_5u,u-11su
_tt €.rouuq csaufi?q

or'..lrrru,lucrzfatrr.drrg1go'.gdro1:ut.trnf(,1go(FIr'-I{reuc'3rcirr;0")rTtl4,nu:-rrxo"u;.i+l1rcd1irala'r1u€'uio.cr'+1/stysn+tsqctll(alriJo.pmtttl.rlczogtnsr.al:rms1,srp:"1fudpaJnpl,3'r%aolscr-lgonrgsr:"-ronnrlls\oiooFuFq,rXplc+oalcolpap"{rarqnos)

{,aE't) rIq
fur

a -;I !,t

aS '+cu+uoc gFql ourIiconcpnupocr?opoc1€npacolc11(g€Ifs'fro1'5^6u$1i)lrtoe?lId;i.sur.€rruulqacJourpri".r.rnrooc1gz.€runIJ1qoFfi€cIaTcIJilEu€;rtrtt1r;

-r{Jcuoc ea.ro1-'ic.rc
,a.r{gue,,sprraTtirs1cuururrurr:rqrlrur+icrolraqrurlaadclul.oyuol{raB+o1'r(sco+ocrltx;p€(rroztiu?or(ioni)urr",ruon:dtrsrcr.rtr1rs{szJrcooJpl €+pouecc1oaJnucoprlcml?uJaoclliblpnDlop-pJ'u€ruu€lu€lcoTocl(q"crn''q}lrlu,Lr)nFortrcrc,iol-rpnnrtuJ?ar)notrTruollScsnr;rnJteooa:pnj}rJurrunrqoqdo'pdoricsgl.rsr'trglypJuaatluasuqr?lsucrIilJt'uFugo(rEcrici{ralrl"opru.u^retuotull.l)rctraa;olstcp,ppnrruet;rI:toauoaJJ"lsltp?dulrrr"lrnra(,iBan-cIrqq'1Iil
-l,llloru In?cf8+uoc €D arnqoJl llrlul luur illc o.Itolur\ o Kqlu'FS ,L tc ll.r+uo(T

{u'r) d[ +"I

--i-- - "

no-',IpclJd1norrppqurteoaxhqS..eo3r'aclaulu.plr1plar'uo,or"nlorauurarrnilJlul,enr€l:rr]r1Jur{oooJ'rJolrgnuJtclr.urrnlrolndJIrJlor,Jr(oIgoSIcJ,1rlouasgu+us;rrfelnom'rud+1ccTooduJp1Iul+pa{Innolruluqpnanr+r,cmusroluaullnoJro.l+nrcoc€t1srtIuc.orfnulclpi1cu1+"otlou;rcaoplprfuJruerntr3rturoi{ntsc-rqtst,I.urnro'q;11zug€ianc1cl1c.iraonuudo;I

o.r?tc ap gepoclsuu,rl o1sa In?uaJnc {41'1oqcs olopop u1 lureuaF u1
t.!,DJx.(,o'u,tLu t.tolp4tnil 0p In]wa,tnC'{

filul dopajului se realizeazd, aqa fel ca tensiunea de strd,pungere s5, fie mai
rrare decit cea a contactului meta-semicond"uctor
[13]. Inelul de gardd,
se inta:oduce pentru a elimina efectul de margine clatorat marginilor ascu-
metal-semiconductor (fig. a.164) uncle cimpul electric
lite ale contactului ceea ce ar duce la tensiuni de str5,pungero relativ mici

devine foarte intens
pe caracteristica f-7 inversf,,. fn figura 4.1? curbele concorttS, destul de
lrine cu cele teoretice: la polarizare directd, n:I$1 (ecuafia (4.41)) iar
la polarizare inversS, panta curbei experimentale este 2,47V1le, foarte
apropiatf de valoarea teoreticd, 2)52V1t4, pentru cazul cincl se ia in consi-
derare micqorarea barierei datorati, forlei imagine. Circuitul echivalent al
diod.ei Schottky cu inel de garcld, este reprezentat in figrua 4.18a in presu-
punelea, c5, contactul intre inelul p qi metal este ohmic. Acesta este cazul
cind regiunea p este puternic dopatd, qi mecanicsmul d.e curgere a curentului
electric este efectul tunel. Totuqi, Ia tensiuni directe mari jonclitnea p+n
injecfeazi o cantitate mare cle purtS,tori minoritari in regiunea rL ceea ce
tlniumelguitleiijaacz1beiii,is.tionEclaaimcreeianasat5pr,eusratiStue,atfoel,rciieltouvrliutmei zidnaeocrsilettaoccroia.mrleautsaetreeonsbailuinnseitrmupcrictiunirairicecealslaizttaoerrfeietaic, tueefnesucte-i
contact red,resor intre metal qi inelul de gardd,. Acest lucnr este posibil cinit
regiunea p nu este puternic dopati,. Circuitul echivalent este reprezentat
in figura 4.18 b qi constd, din trei d.iod.e: d.ioda Schottky, principald,, jonc-
dioda Schottky metal-semiconductor de tip p care are sensul
l,iunea p-rr, ryi inversat fafil, c1e cel al c[ioctei Schottky principale (metal-
cle conduclie

!4 et o.l

z-Si02

n+ 4,2 a,/. 0,5 1a

EFmnmru t V,Y {v+uu-*r/dt/a
a)
'contocl ohmic b)
ol

l4etaL

Fig. ,1.17. -cuCinacral cdteergisatricdal 1-Ir e unei diodc Schottliy cle
NIo- la polarizarc directi (a) ;i invcrsir
Si-n

(b).

n+ AvI tIt'__,t_ Irig. 4.18. -dioCdircciuSitcuhl oetctkhyi-

\ valent al
cu incl de gardi in cazrtl
b ) 'cottact ohmic cind contactul metal-inel
ests ohmic (c) qi redresor
Fig. (b); r- dioda Schottky,
a- 4.16. ii-nneeDll citolleedaggaaSrrdcdhii,o: ltbky- : I * joncliuneap-n, 3-dioda
Schottkl' metal-inel.
firi b)
cu

126

LZT

':c^5t,:-lb--g-v-'a-- * o-l : n@

gmruJa+op

as (06'? '31y) elnu-r{qo relda;rp tluucl ulg 'l?Tl olrro+Krnsprrr cBJ os or€c

ug g.rnlu.reduro+ op Inruaiuop qo1 ed g+u€+suoc autiueur os ortsc (e1uzqr1n

ani-ir{pacu+)ngoAdlpuuroI{rEusa0gr;agrrarn:a;soirppp.cu4rrieugolau+plecsIacrn4zlmpauarortpuuKnoJ€glpsoludsaaugp+rarr.TorSpoEsKol+ryn€a+lu]nstrcsuog4rou(li+;noroFdlpDepaa{U+r:tsIsIoJ€roJg€+-r.p€Fonoolr1l€+paIu'npatpr7d}l1sg3e'a"era60cluugnqmddutorr

'Qt - '*) #\f :lsuoc rs- 5o1

Wl7'p : 2g. am{qo as ftgt) ralipo(rgpet't) apr{ence oropa^ ug pulrr ri
ap f]rulJop
€lit?lor o+sa gltr,iuara;ip u{uelsrzag

x?poxp n a2nr,,iuata.['tp tafuaxstzat na.tD,nlsptr[' g

'i711 4leuro+{€ +rrarnc op 7TV a'1und

o nc otaz\l 1od ep runtsua+ osra^Ip €[ f.r't3Dspiu os raporp ealelrced'e3

'6V - (it -"9) b i-'-1 : eo

;

-'a.ra1+T"rqr uorru€rraa+g?lclTl ,aasa;rappoutrno{elas1paart{(utO)r{pf:'fo'cFGnlpl)CaaplilAalsn:c4rtyLee€.lrc8IsJT}ouclolu.amqaseruapasq+pole€oxr{tsusaafzqp%o{amd?c.oaruspt

'(.1-''-.t)urfatfr :TzJ

(gf'r) ur{e1e"r
-uoerpcpluaocruicrreiuqano.rl€arrnrssl?lEuurscJluoarappr,rurrTaruorerJrzluur"rnrau+iIonarJplosalcisn.prpou:locricnurpauulrooaicsf lra&trparlsrua-aI.Brdalror'u€gqltrruurcJaqnut?lrec{1lupts?uas1urIuI4sKu+aI?O

n4nctyrl'n naunr,swal ap or,jcu,n{ u,g nittnTnndnc na,w.tnspil 'y

J Ol J n pu(,Jrrilas-lBJ Jut

Inlnloetuoa ro.rarJerl ]trulilquI l3 glu]uorur.radxe uo.ruulrrrJalo(I'g't

-rurp e+sa rrts+rrourur .rop:rolglrncl '1e1duroc J€rqc n€s 'l3rqq€)Juo-pdrseuaoucnrg{+c€unouf

ur,lcafur rcap ri (q3f'l
od nu r* egsuace ed apuc aunrsuo+ ep eg;rud aJ€rrr r€ur €ac
?c IoJ+s€ sJolur
dg1'ez1;ru1od elsa ro+cnpuocrruos-I€1om .{ql1oqcg tporp (ru-d gunlfcuof
rS) eiuclrcm.rd d411oqcs lapo1p € KloaJIp arezglelod v,1 '(u-tolcnpuocfirros

tog Rd

+V vba -"/

liig. 4.1C. - (itrlilttl r l'rr.jr aI;igcl.io4d.e2i0i.n- Rezisttrn,ta dilcrcnlialir
:f(I-) ll polalizare invcrsir luriclie dc tempcraturl-r.

C. Deterxtin(ffc{r cllrelrtttl,u,i de s&tu,?'elie, is

oPlol{t,einneS!,Leia} ltdurralesdacepatzicl[ocgnilrtraaecf,ibceuxsltcrlandpjeo:/tlae(itr'imi), iimntIieadrspineoclarteeriazlzaalrleaiaxcalirccuctrire, n(tfuigh.i4l.a21/j) :qij,s.e

q',,: !r'!y\lJ""f,{17' )

D. l{tisu.rarea curucteristi,cilor spcctralc

CLrntactul metal-semiconclucbor poatc fi ilurriinat tlin parlea clinspre
metal s:lu din partea clinspre semicontlucbor. In primu caz se zice cii ilu-
minarea, se f:uce din fa!5, iar in al cloilea caz din slrate. in cazul iluminii,r'ii

din ll:ltri sinl excita!,i elecbroni din metal pe nir-ele energetice superioale Di
clacii Lv)rD, aceqtia
trec in semiconductor (procesul 7 pe fig. 4.22). Dt
zlseillellea,, dacil, rnetalrrl cste suficient de sublire qi iiv ) Eovor fi excitate

perechi electron-gol in semiconductor (procesul 2 in fig. 4.22). Curentul de

sclrrbcircuit sau fotocurentul trebuie sir, aibi, o d"epenclen!5, tle energia
fotonilor /r,v anaiogl cu aceea a fotocurentului din cazul eurisiei din metal

in r-id. in cazul fotoemisiei electronilor rlin metale, cruentul pe foton
absorbit estc clat de relatia lui tr'ox-ler

EI- (ir, - )qQ>'12, hv qtJs, (4.51)
[: o, /rv ( qtD.

l)c fa,pt aceast5 expresie este determinatii la ? : OK insi, ea este valabill
cu bun5, aproxirnalie pinX la ternperatura camerei dacl lucrul dc ieEire
t2re0b,u5ieeVs)iiqfiiedatncuir,lt(/prvre-a O) dep:i,-
(sau inirl!,irnea barierei) nu este mic (',{D
1trlte cit-iva h'I. Pe de altd, parte /iv mare fa!5
nu

rle qO (hu < 1,5qO). Rela!,ia parabolic5, dintre l? ,;i (a/r,pv o-teqnOlia) lsueluuiticli1zeecaoznir-,
de ieryire din metale qi
pentru tleterminarea lucrului
tact rnetal-serniclnrluctor ryi metal-izoiator 116]. IiddS,cinrr, pftrafti clin ll

128

szr It 099'c-6

I .(q) r1,sV133{V li; (rr) u-svEi)-tV
rJnlJil.r:ls LIr :)IJJJJIOOIOI rtrllllrriiJtl) u !lE.r'Irrcls llJrlr^r,rJlJU.rrl:] -, 'f r.f- 3 i:I

(c (D 8?
l\a'L\
J t'r, 'nq
i't z't i.': 0'i. 6'c'

o
c

AA s

Ko'"ISrIorTo+JICc'l3nSApOupToa+cIr+IuIszraaosr-tplIuroa+s-aJuto'{i+;1cI3nni}pocuqBo€+c+uruourcoIs'qlgInlllau}a€ZJ+'nZ$r,s-l,f}:ln'r1uJ1++:uucot's,c,1l(u@moclbn?o-rpro^JaEnil)c?o-r++uogaJ-+€oqa3dFga"rlI€o.uor+np
-caals €'+uopuadop Tc ?r??K"rE na acr,lo.roo? r+tsJoprsuoC 'rolrJolcnpm{icruros
B asrzro:lur rrzuoq IIuIFJKI tsJ.r€urrrrJ0q.cp n4uod rs cu cala Inilru{a nc r3

uJn+'r3.rodrua'l nr +c€luoc op rnlnluiualcrl rai{Ur.r€ lnlpn?s nJ?uor{ yzlea./rl
-I+n Os IJollJnr'Pru €OuoruosY'InlnJoqCnpuoCruros € ssrzJa+m ilzuoq €"tuilF"rFl
nc El€Fa s+n'a rI ;rolanpuoorruos-l€lour ri ?, Jo+cnpuccruros-I,r?latrj l?€'luoc
qAoa(srpa"IyigzJuSnorgrloct)7glf,'tI6g1]:r'ui7ua;'?(apDri1Arb,orsoldLyJFotgs.rlr,agOio1:ttg-al'lArr1:JF',att-rs'atqog@ulgaoagbtpf€uorr:lr"qt{nq1]@sgqnu,.,bgrrlcltauE.rtgrcur-rr&rc+Iuaarra.:TrIaloi€-l+pto+Jo+BurpnSIJnlonuqnl,oBr-ruDi+loopnlrnSullxznEaa'Jcl6.opr-nlriJcr)ct?lrudu^cq;r+pr1gitgncfo,uzmgporol:.{Dr!r,.uti,1.t.r]r){',a?ri3,lrzpfp{nc?b-.aoarradJs*t

'uroJJ ulp JoliuoJl 'JOIJUpUOJTU|JS 'u lfJ.t l1)

-JJIJ IJrsrLrilolot u uletJ,tads -JEJJrrr [lljcr]:lu(]u uJ .lolruo.ilJJli) ,r.rgzl.1.:igCI l;l -g11ir;r1.l,i lrit)Olp
uJrlsui iJu.re:) - 'te '1. 'l-i:T -olot lrJ.tuiJLrJr) lj _l / lr.)llslJ.rl.rl:,ll: t '{:. .i'l:l
. , .eC'T. ..tlrI

ilel aV e-nv0 .<n --*-:
,'g a'9
j i slur

ful

uI :Fogp+6u€'ntIouodrp€nr.'Slrxrrraor .raclsuer'Opp,rrouorudmuolKJiuo+lucr€a"ralaou+notsrpiisJr^oruEdao€r+xiotJsr.qnllJco'luprJaodldr{{oncJ+upBn};uInruizicIaaJEs+llau'eg1+umua{rzz1aogJ.rrdTaa,.rrpoa1q-ls.suao1

Tabelttl il.4
\ralorile barierelor Schottky determinate experimcntal

Semiconductor \Ietn I q@6, ev

n-Si .\u 0,79
p-si -\u o,25
n-Si
n-si trIo 0 ,59
n-Ga.i\s
\v 0 ,67
n-Ge r\u o,95
Pt o,94

Be 0, 82

.\g 0,93
0,87
Cu o,8

AI 0, 48
Art o,48
Pt
;\u 0,8
o,35
Cu o,45
0,58
Ni 0,86
Ag
Pt 1.,34

Cu 1 ,14
1,34
AI
|,52
-4.rr 1,09
L,2
Pt 0,48
i,Ig
0 ,45
Ag
\Y
-\u

4.6. Strueturi eu afinitate eleetronie[ negativi

A. Diagrama benzilor de energie Ia su,prafald,

troni IJste posibil s5, se obfinl stnrcturi cu afinitate negati\'[,, pent'lu elec-

la supmfatS,, prin adepunerea pe suprafata cumtd, semicon(trL1ct'uru-
lui (d.e tip p) a unui strat dintr-un element electropozitir. sau sl,rate alter-
native dintr-un element electropozitiv qi un element electronegativ. Vom
d.iscuta intii efectul pe care-l p oduce un element electropozitiv ilepus
pe suprafala unui semiconductor. Elementele electropozitive ccdeazf
u$or electronii de valent''; iar materialele acestor elemente au energie de
extmclie mic5,. Prin urlnare, dac[, se depune pe supmfala unui sernicon-
ductor un strat d-intr-un elernent electropozitiv, semiconduetorul ling5,
suprafa!5, se va imbogd,li in eleclroni. Dac5, semiconductorul est'e tle tip
?r, concentralia de electroni primit[, poate s5, nu afecteze struchra clc benzi
la suprafala semiconductorului in contact cu metalul. Ifn asemenea caz
este reprezentat in figula 4.25a pentru Si-ra pe care s-a clepus cesiu. Dacd'
de tip ?, tle electroni prtmitS afecteaz[.
semicond.uctorul este concentralia
considembil structura cle benzi semiconductorului in contact
la suprafala
in jos (fig. a.25b). Afinitatea 91 a siliciului
cu metalul ryi acestea se inclind,
acoperit cu cesiu este 1,4 eY, atit penhu Si-p cit ;i pentnrSi-n.
in jur de
Ins5,, aqa cum reiese din figura 4.25b, afinitatea efectivd, q1,7 (m6,surat5'
fa{5, de minimul benzii de conduclie din volumul semiconductoruiui) este

1_30

ttt

-opu! also gsul (ol€+uorur"rodxo olo?€p na Kp.rocuoo g{eg.ra1ur q lurfua'rod ap
oJarJr?q reun u{uelsrxa oundnsa.rd e.rec lopour +sacv ',,r{urq"rer;.r ruoJloa{a €c
(Aegtg-7t0 nc gle5e plrlrzod o+tslrrrrJ€ ap) urnlsaau tsJorJ€q azap€Iuc-\a g"- 1od
AtOfut-srfClIeI luuInlrJro3€?uIcnnfrlptaurroSrcrgTquuaroro;srlueqJu+?gs+tssr{tsouo,.crrteusuduey18;r'ucnl,uodz1oeqrle+oupcna+OlzgTsS'CAar-rJnIIlanIzrroaop??qcctnnsppcsuuaooccorrrmupa"a.-rso-rOEapz1scorC+d
'-qslroT?Sco€,r9uD6'7eJl€:mO5-sryC op Inlrr?J?s o.rtsc u.r ounr{cuofo"ralaq Flopour o+so Inurl.rd

rrl a+€?uoza.rclo,r eloporu fnop g+nlra A-III .rolr,ro1cnp
-uocluros e,iegt"rdns ed g-s3 op JoIrJn+€J1s g.roundap Inz€c uT o.,lrgeFau a1)i{roJ?
-ca1e rr{e1rur;u ri"rour{qo ra.recqdxo n.r?uad'[gt_l +euoplo lodrp op +rr,r;s un
IraoJlr+"srrtus uoSs-rnrdpnusrruuaJpo;y'zov1,aaSvarelsurr{prq.aropsrpne{unulSsouc roptzgr:rauoiu+1a1s'ru,ranF{ulxuoi ap rrrrottr rtsI

ur.rd atqt.rtdas
u (OOf) u!,u;elrlns ,tri
'I'to+uocurp'r3 r;rturS u7 pz,eatann? os rruro+u rnlucrps pa
eundnso;td oS in;u.r.oqe.rud u-iu 'I>111oqcg prlaaya r'i
uI +E+ncsrp u-s runa

.rolrzuoq €a:tuq.rnc ad u,zv,azvcl as Inuoruou?d 'B.1ts+run nc glu5a -trlurruxo.rcle
a+sa y.rgopr-roJ?ocuarlsoo€JoaeJ€eIopun(?ueobpr€xool€a+pqrqcerrquoo.r+duoeu.rorcruu+r,ErdJ+'rsnlnllrucrnls ui+:p.rdn"-

sd e rode rS
er-Eur.z;srr€roa*aDdaruxroaJaoppJtlanc{orrucuaSnrpolr!',".grrt.se-asorCoudo-u:rrrcrgg+iun€.rur1,pi1sr}rus:Iern'rdoxu1ornu*nrrpa1€llqroIluu'a[5nrSodarefuJ]ptsFAqJuorrur,6aordtJu0+)nc6,oEr-laoos{.3.ruaEa+1ot1osInu?dr^rrxuy'orBJeuItpsoa;lT)rqrnlt]',uprit??aisorrauuaanrss
ua5rxo rS nrscc op o,trlr?uJo+I€ ocruo+r?ouour o+€J+s untlop os pulC

:La t6,z 6s a.rrd) o u,rt'"f; ;#" .ff"Jf"$;";. 1"39$# #i fd;,;';iJ:

o+sa z?c tsououros€ u11 'parleFau f^r?caJo KcruoJ?aalo al€+rur;€ pm,iqo as

TE'-s1u'SytuoI+d€cncrolCslaupaJacacs'ArnuLnaa'rrageleu?tlqgoBn.urlt:IrlluacndrlJzoI-cu'csftlsuyFlu-dcsgerypqtfsn€S,fequ'Ou:+oior:opcdaxapTK?bsco'TgJlo€,-'dJ(rIqug,-'sITrSS€€:Zutn1'rrfor'Xq'+3gbtrust;r)TzooJouda:.r+r{acu'ozX1l ,DoK,or+fpoas-usoXl€uuq'foo)s'rnC3?=ccnlaltocc1"laaIar.firrrJuu.,rroaaud1idluorcoJcancc,tpBtssl

a'dJ-E.{ou:l,J,)llp-uopJnr:rJrsl-so\liuBuro-):lu-uar : r1-r5 -q :lr-rs^ - r) : nrs)J nr rl!.ri)doi}t:
'gA'i' 'n-1.,I
.rour-r E IcllJSJrrra rruu.ri3e111 -

o>Joxo a ha +/'l= u a

,\e'/'; D
L
JA I
!7
A= ta7-b

j

12.

eluod 'opdsiupg-ercol€1^IconJop+upsovc€orpruguatsnsqcue1pplu'dl$earddrr1or.lorudpuarintoxroloJ+r€cdone;puF]ouucorl,ralr.rofo,psInaulloul XolrDdu rollzuaq €aJ€u

-r1cu1 nc '4edop cru

-.ra1nd qcap €crur r€ur

ielnic er-i un strat monoatomic de Cs-O poate a'y€a o structut{, de benzi de
energie ca voiurnul semiconductoruiui CsrO. A1 doilea moclel, reprezentat
in figula 4.26a, este cel al rrnrLi clipol tlublu cle Cs-O care se formeazir' pe

-C IgXef . O
!cX(csto />o

F o AgXet< a

llc'-rs-.z0-It "- _{ rn_:vid
a)
cs2o
b)

IIiIigI .*.1\.2'G.(l-s-OI)i:agara*n"rarncokrrlbcchuii;rhi ctlottrconjocrngcic{iulatres,upDt-'afanIatodscenluricl ocnr.rriuccltipoor'l

suprafata semiconductorului ryi care detelrninii ingusta,r'ea' si rrrir'soliu'e&
barierei. Grosimea stratului de dipoi este de a'pro-rirnat'iv 8A astfel ci plo-
babilitatea de trrnelare a electronilor este mai miczi decit unitrr,tea, eristincl

o barierd, efectivS, deasupra nivelultti 'r'iclului (fig. a.26b). Prin l1l'nlal'e,

in ambele motlele existri o barier6, pentru electronii care ies tlin semic,onduc-

funil fIf-Y ceea ce concordS, cu rezultatele experirnentale. Rearniniim cd,
a,cest aI d.oilea rnodel este aplicaltil ;i in cazul strucl,urilol clin Sip cu afi-

nitate electronicS, negativ5,, ins5, de a,ceast5, datd,, arya curn s-a ardtat mai
sus, datoritd, mod.ulS,rii in spaliul cu clou5, climensiuni a suplafelei (100) a
siliciului, grosimea stratului de clipol este de aproximativ 34, r-aloare
destul de micii, astfel cd, probabilitatea de tunelare prin el este practic egal5,

cu unitatea. Inainte d.e a depune Cs, O, sau alte elemente, suprafala somi-
conrluctorului trebuie s5, fie bine cur{,{itd,. Suprafelele seniconductorilor

III-V se curllti in mod obiqnuit prin tral,are telmicil in r-itl . Temprrlil,tura

de tratament depinde do material I oricnrn aoeast?r' trebuie sii' fic nriri nricii
clecit temperatura sa ele descornpunele. Pentru siliciu supt'a,fc1;eie 1ii1';1{qr s€
ob,tin prin bombarclare cu isoenci ldeepuanrginons't1riattreatzml,ounreonzrt'toinrnvicied kl ttlurl;t'r'nlura
in unelt: ttrzuri
de 1 000-1 100"C. Cs ;i 0
succesiv iar in altele ln acelaqi timp. S-a'u mai clepus strate do Rll-O sau
aICCnfssi(n--AFOits,ao,GtrePia,)(ceA:ulsem,CcPtsrao)-mOn:i,cCaGSsm,aniGPneatgi:,taAtlCsiav,sd:i,,nCGcoseab-FpAliu,nstGu,:tancOu(Amsss-iaOn'iS,tdb(eqI)iCn:su'.rCGmPsa-rilOi)tnt,;AtlirS,serci rl:e:lrCCr:'tsse--GrOOiai,l,lA*tTrrsltetn(:APCcssu,,:
P) : Bb-O, (In, Ga, As, P) : Cs-O. Si: Itb-O, (Ga,' Al)As : fls-Or GaN :

Cs-O etc.

Its. Probabil''itatea de ie;ire a electron'ilor clin, nmterta,l
Materialole cu afinitate electronicil negativi, se trtilizr-'azf in gt:rreral
ca ernitori de electroni : fotocatozi, emitori de electroni secundari in foto-
multiplical,ori, catozi reci. Existii, trei procese de bazi la fotoemisie : (1)
excitarea intelnd,; (2) deplasarea, electronilor la suprafa![' (3) ic.,,qireain
vid. O comparalie intre fotocatodul obirynuit qi cel cu afinitate elecll'ouic[
negativS, este reprezentatA in figura 4.27.In prirnul caz (fig. 4.27 a) elec-

132

ttI

'(ulduaep ) oun1ff::.r f:so-llu,crJ-1rn1lliustp31sauocpotr'rs{c64,ur1€iuryf0+nuauIrrusrc-cd*xJ1rno3tq8ssgosriolo0urroJrr[oc+pr:.lcosrooll€rcl7rouaagorruplalnrnt.al,lru8B}'1r'orouIuBJ.4irJra,4.)ussiuuE'lrIIondi0cr8lol'nuo0pan.rt,oo:urt?s]iI
Elscrre u! Ft.IB es pule r* (uFu11s) aluu o-.r€"ro[ld(a.rcoolrzru.arqolrE4ogJlqr:.imlqoduwl ra€]srio€.srJ4rir,oocpuuocu
a-IplJuOIllJlloBl-urlzuJo)q[!{uroa.ur}urJ1I8Oa.reuri;nq1iru.r1lsearptu1ri
1y e
crS
-.ralra ap rzuaq Jp uruul.qeJll - 'gi'i, 'S!..I

l3lu (qs'r) ( ",{

{Biu '.,,|\.-",io ):,u
-\- eriela,r op ,!.?,1€p ag-so (alurrqcu1 lrrls olrzilaq
apun) o;uzrndo op rnlnl€J1s taurri.l,rngl
I3 '96'7 e,rn8rJ rr! €o lc qL6'T e,rn5ry ur rc

K1ts.ru nu er.8.roua ap rzuaq op errir"r8rrlr
uI'JIE{,ra}€ur o}IuIaIa) nc ol+€,I€dmoc u,I TTIEIS a'1so rr{.q,losclq? apun
'a1e1r1ua,r lniuaurop TrI rorsrura ,|3iuercr;a atrioJa
'aJ€uI elrllculp€ o 'c1 op giul
I,BJlJads
I-arL----nlu?.i?csLrr"r3,orarZ.rpocrguoal'ItTJoniols1ucnl€cnea+'T'unapuIpt-crrLrulIsagnaZo1pprapp,anu'r'uaTal]lrl,Erululrrdrr'€toaurlIersurIs,auDprrutne3oragl8tr[l[rssru{rrJcoBp;vuo€rTruosp]'E:cIpeivJInpSI€onzlr]ulorawoiIBoapn,rsro1pzK(orrrrSruolrciunarcEcrcdns{Etqo,cKuur.rroacS'aurotil.o*orue,}(iruzolrgrla'or(ir.DaIto.olcirai',ppErolrpJo]luaptonp3rrondn?soInutpiztps*rd€rnss8e,rsrorJa1olitlI[tcuoepi('lgoooJ8lKJe.lrtenlrcfatlptcut{lslllurn.c'ot{ro€rs-p?qncq,t"uc?Iurlr?ornloqau5cJn'cipoaut}orssJlrnaaaul?l3lrpu.ocoaiol'arul+€(pucalBnzzor;4lieu'ptrrp-ualouciJuatrr}qrieJ'r€recit.e}3]zrIIeIruounptpnlltrlierelJacqlrr.ur'?ttrur4?Juurarloliolomu:nrnIr.ra'uSru1crtlI
q€1'Yi4uY0Sr309i:rIn0-slrIe9pK6oFDpaJ]ppJor€ru.,r)IlrlIduD-tuituzioaeIpratlerzsrKlop"neioiraupudr-esalA.rralaleTsTurlgo^nrqItlluccuoolq,irrlltlruuuroorlta.crJxtIoI{azuqoI:Ila)luaIpnJou.eurn]t!I$),.Ie'rpllo.aIulunoFcc,orpn(l;cooiaJ"6lrluid6rt'{rutooi;u1rtona,"a;r'raepll,tcraolDo,lrgutt{l

lnun-JluI ri '(q) Flllu""ctl rl ulltl trc n.)
](juzB) JgJ,llstgnzlrood.reurlEalliFrr.llat€u;rnrrl)[BlzUu;Ji](u[urtpuull-tt,tIe]{.li$l urriu(I:}i-r-x'la,2.'rfo.'ll.u"o!-..Ilt
-ea1c ea.rlior

(tY^fu

J

un ed Aorrr 0g ,l11tu4xo.rdu arS.reua urp p;rard saac,rd '1sac€ uI r* gf'e;t.idns
l*no.r e ruluad
ao;Eld+s'pZzrbes?u.rlacaleppa.arusrrrr{ru€1u1rcnx€asnprr1ouJ.3locoalr'.g8;ra'IT€r+oaKruqruB1gpna?osln€qi aEJs?
firgraxa lruo.rl.

accelerali d,e c5,tre cimpul electric intern dirr aceasti, r'egiune. Se
define;te ca probabilitate de ieqire, B, probabilitatea ca electronul ajuns
in regiunea de sarcind, spaliald, s5, o traverseze qi s5, iasd, d.in material.
Electronii accelera,ti in legiunea d.e sarcinS, spa!ia16 lrsi pierd enelgia prin
ciocrrile inelasticS, electron-fonon. Ca rezrl,i,al, clistribulia energiei elec-
tronilor care ajung la suprafald, este mocliticat5, fa!i, de volum qi aratd,
ca tr partea cliri dreapta a figurii 4.28. Electronii cu energia deasupra nive-
lului 0 al vidulni (cuprinqi in regiunea haqurati, a rlistritnifiei) vor tunela
prhr bariera de la suprafali, iar cei cu energia cleasupra valorii barierei vor
Din examinarea figurii 4.28 rczultra cil B clepinde de
ptrleocfeihlirleqstieinadc,Ie{iarnsetaa. barierei de la suprafafi, qi clescreryte cu cleqterea I5,r-
gimii stratului cle sarcini, spafiald,. Dacd, II/ este mult mai male decit dru-
mul lil:er mijlociu al electronilor atunci electronii vor ajunge termalizafi
la suprafald, qi nu vor reu;i s5, ias5, din material; prin urmate B se micqo-
reazra. Avind in vedere ecua{,ia (a.ir5) -B creqte cu creqterea concentratiei
d.e clopaj, No.B este afectat' de contaminarea suprafelei materialului. De
asemenea, depinde de orientarea suprafelei crist,a,lului. De exemplu, pentru
Si cu suprafelele (110) qi (111) acoperite cu Cs-O nu se realizeazi, condifiile
ad(1e0G0aa)fiAntlsaitataatcetoi,peeilnercittadro,cneciclueSa,C;nisce-oOgnadsti-ivlai5is,oeqboiliBbnluinebseteBBz:e:ro00ri,n528t.irP[n2pe0n]c.terupesuutprruafsaulapr(a1f1a1la)

4.7. Fotoeatozi eu .atinitate eleetronief, negativit

tr'nncfioneaz5, in doui, rnorluri: (1) prin reflexie, cind lumina este

incitlent'i pe suprafala catod-vid ,si (2) prin transmisie, cind lumina cade pe
substratul sau spatele catodului. Primul mod de func{ionare se utilizeazd,

in fotodiode ;i fbtomultiplicatori iar cel de al cloilea la tuburile cle televi-

aiune.

A. Mod,u,l d,e Janc:!iona,re prin reflenie

Eficienla cuantic6 de emisie, numXrul de electroni pe foton incident,
care ies din material, este datii de expresia

t(A):r. B(1 - l?) (4.56)

\ -f IlaL

unde B este probabilitatea de ieqire daeexepalerbecsstorioerbnsliileeorgadisluienmgmtienaiii,ntqemir-iLaull,-liInlldu-nsgocirolnueelfiiaa-

dcieenct,luifltidz"ieereafleexleiec,l,orco-nilcoor.eAficcieeanstutdl,
ecua$iei de continuitate cu B

t) !'u - 'nE +G(n\: j?t, (4.57)
0rr
At

.(1- Pentru gdsirea solu!'iei ecualiei (+.57) se presupune : G(r) : &e-qr -
E), catorlul are grosimea infinitS,
qi se neglijeaz6 absorbfia pe purtd,tori
liberi. Pentru aL47, r'elalia (4.56) se simplificd,

r(),)= B(L-R)uL, (4.58)

L34

9tr

ur{qo os r* uri 6-T Iruuaurop ug o?sa "ro1 eeurrso.r5 aaa.t€oop ?11alJlp r€ur a?so

arsrur-su€J+ m.rd. gzue.ranl o.rsc Jolrzog€c €aneorJq€d 'ger+rJc oqsa nu rnlnp

aro:-nI-'-k--ur-roqlo+JJosco+pJ€lo€€(I€t"Y€€ops"lrc'crecplA*nsoFruuqnpcoJ€€oee.tIloaorr(oeppu+noJlsupoL€aBpuJe4y+i'sarpocrlo;s€rt{ueunlsdnJ.JonOe.r"apqrlcJiuol$dol1€dn.?SrrnOpn,uiqeua.tnsuI'.eusacurpIa'r4'rlanogguoocrdo.rrrrFrcail'pzperI;ei'€edlf(qnoreocsIoJua.Jloo=.nragoprnolr+rspdlrc+{uroo'eegnrtprasoa;"nulsrodrIp.?uuluor€,dtueE€srlul?ilrmuqSa1ge[grasoo8rl+1pauaorn.errs.d4xa1drcu19€)lr1ouicr+o'rune1Vdrauu€8rcsorro)qIlt1npuasprer,,J{u.l'nul1cr'pe'vnoroopl€yIeoulrdScrsdee+clS?aJsar:uTsoe'roro+{o"drorr+pheouenleoo1$ougxursporpe'rSoxr)d.s1*earrq'ocps*gur.o1grtl*scllanu5(<(rioun(l.rIrncrrrprn.aodoura'cuzqr€'erno*egrrlaguea1.c.€p.lrrl4lrqsuSrdudiaeuruluarx)1Jogxore-"osEn}€rd€zeceoacplc€u"on}rrprrlraa.op'u/t"nrurg1olroroclSJ,i}orcaJlprnmteln'.splusulroac1iocproScoeoa..zll€s7ndlaJllaroas..c€{ctr.rlJgsoc.riuog.rzon,:;g.1eo}i.aJ1p.ntE*grrsot€eao,ua+eraalc.xr1:r1rurl,rasEz[Lc,errrr"i.
a'lptZ'p]up-1+ev1ctatdur:uro,iuoyr,rueugrurer€sIorlrduxroruonla€J€oKrxcarllulatsl nocpeI{nuluaarorcryrJaazovccolspaactpsmudIap eg

alsllusunq 'u't,td a.wuotfcun{ ap Inpo6 'g

Io-t.,srueu.(rradr']aIenppu'rer1naoll1ns1larur€ae+lln1r{cuurrslldr?l'egruu1rouxrutjs.ouu1ar{lguor.out€aooc[trnsroz,.1}rosluloa€eoouco,lnt+uodo,+}u'Jrp€rruuro+r{!ll€I€q1Kacc€a++,se,sd*€duouoncorlp€roplp!eurvunl"lrrrlrnlaitrr"ypOrsetuaOuiocoffcrt(t,sogfgoo.rJu€^aann!pplrl
-r5au gcruoJiloala o+tsliuiJ€ no rrzolto
'ppun op I caurl$unl .62'l .,qlrl
-oloJ uI 'aruc/ysr:gT Inulp,to op (arur
op )rif,unJ uI grlluuur r:fuelcJgg -
el,r€oJ olso !ar]€oqau ?Jrno"rloala a+ts)
*d'y
--rnrrlwrJ€anpcInAlu-aIIJIncr*n'scylu€roocmnp,rlruzaoc+l€ccro.rlaoul
t'I o't s'o Ec /o s'o sb
n.rluecl rq/Vrl 090 6 op else glelrod
-rrr ol€+rpqrsuas or€ru rtsru €oO 'rut/VrJ
lo'o rg-,u-'--slerarlrJq+gI.€uVorrIJa0rKsn'ndeuurk'€0nococ-oc,srruose'lnsIu"uar'ggs-r3ra$2imnr0'.dsrgourig'0*o0lrl'O,"slrtTr+Zruo'ozuoqZfFr+-lrpzsrl€?Ionq€oZr€?0nrotl€{O"ugoOcecurlu'rrouOif+pq'lg.o''eur1o.Ir.Jl."uar€0rurEranq'.€0rr-"cdcees-es1ptgoOdeduceprslu-r"aacoslrsosf+Cr.u,r1ryrtJeseemuno'rlugrr+acu1f*rl
ETs c-o-6v

-calap n"rlued olrsolololol'r3r.ra1ew ! prq

: OyI rnlnros€I e tutl ggtf op gpun op
t-'o eemrSunl soJo?m qlu.rza.rd'n1c{urexa
oC'Kpunap eunFunl glrurnu€ o n,rlued

gorlutnc eiuarcrJo ezezlurrldo os Es lr+n
olso
alsa rr{en1rs a?Inrn uI 'crru r€ur
,r +Ic nc oJ€ur rslu 1I+€ nc r$z.ro+ul
tpu€q oJ€ ar€a uslyp"-Iri€r -vg,II"nqzolJnsoncduraraooc
-'(uOaDze"-rded.gr.)olrsaoiu6o"zr'ef;rep.reneF.rra; lSuef.,r'cAnnc n,rluatl 'g.rn8ry
a1*a.ro gcrluenc e,iue1-c1gg:[iZ] (V)t" p+sr

lnsnpo.rcl nc gleuolfrodo.rd o+so ?crlu€na
eiuolcrye 'rnlnpolra e1r rarlsrieqctsr,t?c o+rurnur n.rlued go Kl.rasqo os apun op

prin cl'e$tere epit,axiall pe suporli din monocristale transparente. Astfel
de supor'li sint safirnl (Alr0s) qi spinelni i\{gAlrOn. I)e asemenea, pentnr
lumina r-izibild se foloseqte ca substrat tlansparent GaP, carc cste trans-
parerlt pentlu ).>0,55 prn, iar pentru domeuiul infi'aroqu se poa,te folosi

ca su]:strat GaAs care este transparent pentlu i. ) 0,9 prn sau InP ca,r'e
estc transpalent pentlu tr ) 0,95 pm. In general constanta rle ret'ca a

substratului este diferit:i de cea a stlat,ului activ al catoduiui ;i pentru a
realiza, o apropiere cle constante se interpune intre substrat ;i s'rratul catod"icr
un sl,r'at trallspaleni rle acortl care si, aibi, constanta refelei egalir, cu :r

catodului. Structula cu trei stra,turi este reprezeutatit, ln figLri'a 4.30. Dac::i
se nt ilizezlzd, urr fotocatoctr de GaAs se poato folosi ca snbstrat uuul c.lilr com-
puqii tel'nari I rr"Gl, ,.P, Irr, Gar-,.AsuP, su:i,coiItnrc.iAdil,r-t.'r,rAasr(Pla,.,\so(tNco.l,
cll
asernorrea cornpozilie incit eonstarrla relelei rittt

cX' constanta le{elei a conrpuEilor ternari qi cuatet'nali variazti cu colnpo-
zilin n (qi g)) [4]. Dac5, se folose.ste ca fobocatod pentru lungimea tle uncl:-"r
de 1,06 prn, InAs.Pl-cr se porneqte de Ia substratul [n1] 1i se folose;te ca
straf intermed.iar fnAs.Pr-" cn bancla intelzisli ceva mai tnalc tle 1r1 7c\'.
I)e *serneaea, dacd, se utilizeazi ca fotocatocl In,Ga,--As se poato polni

de la GaAs ca substrat ;i se foloseqte ca strat interrnerliitr uu strtlt de

In,Gar-"As cu banda interzis5 ceva mai mare de 1,17eY.

Sensibilitatea specb'al[ pentlu fotocatozii care lucreazd, in t,ranstnisie
renstarrxciernva5rnoabitminicuXtd, d, .epceit npetlnublustcrnoicctraure'aluGcreaaPz/irG, ainArse,fPler--r"i/eG. aSAesnsiebsilitteatedae
ti3u50liig.GAallPrn/Gta2.a,.lA. 1inr-f.iA$su/GraaA4s.31fLrers-rtecfiroenpinredziennttaratin, semficiiseine{ai,"n'cucacnttmicdp,araa.stiberucc1-l
cazul cind. functioneaz5, in rcflexio (strabul acbiv estc GaAs) ; serisibilitatca

strncturii la h-rminil albii oste 320 pLA/1m.

Q. 'lltlicttlii i,n telettiziu,ne

Fotocatozii cale lucrea,zir, in transmisic se foloscsc irr tubut'ilc clc irna-
Coapttoicdiluliudtre'-teoctirenaaz,igr,inseerf-ontrorae,llencl blurircndi,n. rIxnt1teiuirnptulrllrccon1ivceolsnieviesrtecu;tuerailmnlau-i
gine.
ginea
lumilos in semnal electionic sc poate produce o dtrgt'zldare a imaginii in
fotocatod. Legat cle acensta, o caracteristiciL irnpoi'ta,ntf a fotocatodului
ntilizat in tuburile tle irnagirie esie rezolulia spatialir. O m5,surd, a rezo'
lu!,iei spatiale este funclia de moclulare c1e tlansfer FMT definiti, prin

reia!ia

FIIT( 'r.1 : ^T-o* -T '-tn- ,

1^u* + ,l-in

unde f-"* li I*in siti.t valot'i1e rnaximX qi, respect,ir-, niinirn5, a1e sem-

naluiui rni,sru'ate in punctul dat;. Iiezolulia spaliald, limitS, este definiti,
ca frecvenla v, penttlr cale Fl[T(v,) :0103. Funclia c1e moclulare de
transfer clepinde de frecven!,a spaliali v, qi de caracteristicile catodului.
Aceasti, dependenld, este determinatS, tie difuzia kltelali, a fotoelectronilor.
Cu cleqtcrea vs creqte gradientul concentraliei electronilor in interiorul
crtqraaiurvteoaparlalouFtllriuMluei Tcrly.oui cmOilelbcaiipsnecealrrelnir'ie,tsrnatueelea-q1litu3lcei:up1are.en;n-fcintl-uetnlhlldridbe,duedls":iiltfeeu1zrdpieeerpnlria,rentsezare:ganlidn0ta,e.tcSfflooieincnatalcnifeziogadturauertcaaee la micqo-

4.32 pen-

pe figuri,

elecfroni-

136

Ltt

'Lr(p' n)( il*E)ar - I dxe : ("n )Oni.{

[2,6] 'ersa,rdxo op E]tsp
clraz6ro{ocltuaano"grloor'dJIgor:grlrd]suoolarosp;ruatrJsrtu+sezoqrrrl€l(cumot1Jrcdrl lElcnzp€tso,orlnreclccnnl oJo.l.rsr€ecanrpr€llurclae'pc8rlon'I1.r:con?;s.ctu1luesor1rg]+oosoptlseoocJot1uu{lJnT}IpIT'onIJlIuEc{aInSpc
urp uocrpil X+uii o ntss Jolso; ap uEJ?a un 'tuo.rlcala op ro]€crldrlpiru un ry
ge'eilluer;eoradlslarIponapoeo-.uit1lvpui.,'ru1crlcluo/rrir1o|u4ae9rl7+ourlaI puenoltll;gtdop1os1sdtnelonoursfuuplrtgo{ curaeeprig*tiup1nuox1;€statrlnropts.oIaluu]ubl]I'rsiSrur1laun]u1urr.o,r1t.?rr{ca14I'd1eJcip]esadp

Aor-3uT-reoId'IcpIorriSueu.znroiliudepIuzlogror+J]s€'u+casuoxl"salrosaa1urorri".aropaJroresduazozlIlpdvouau+rrEanrcapr1t€rao[l,Jrr,a€nIzpotlruIK€rr€cJnroa-,rJrl1€]ot1n.ailarln.aicdoel]uJoclrypc8,elIgautiornirru+lrraoc$pJnelJciIu]ons{lqo'aognp1uf0led1'lrcr1'ill'uoglqJs.rlar,unrcJalei

z'z 6( Ae '4q g'I s'r Y't

s7 8't t'r s -ol

a txal|al! oc
ets tugJDJt

nt's\,,rrr'l')ius,Vllr{r-r1rn1,1r rruriurr,.1,:J/,r1Jc11I .y... ll.Iitl)n.l:s
'lg L Sljl

x ,*u"_'/ ts ztl-'lf ---Ti5lrbl79Z'o oo
sY'
\ rlnl-i_--_

\

\--r-x-xxxx-x>x

DluDl s lo oto: o

D*
;o
--f,

a

lilL_ .tlr1s,r.ru r.r1aio.t

rr::zlri{:u.rltsrio:otiJrru:(t.l.rr):nJiursJirur..rml rJrtJ?,;.ir.ilslttilJtoJu?l lrr
r:it

r:rir)pr)lu)ol{)j lj nrl.ru.ll\ - 'ot: 1. '.::!rl

" ft q

r-j,,i-*r,r, :,! ;:"r';;)
t : vals JWtSEnS

SiooJVS
rY urs

t-uacuoc o.roJs ?uls Inpou'u ri inltolzc cttillsJaaur cp €m+?n-Jls uI 'o,rardolt{t
oonproal,sr,rr3nzrgl€ncooJp3?p+insrrrxogJS'cISrlitIsslsoouJnlclso.lIaoaoucr€JopasInptouue€?$qs : Inlnqnq ati.ln.rlsrroc op
op 8.raur sJBa JoI
poT3o q

unde Zn este energia maxim5, a electronilor emiqi, vs se m5soarX in cicli
pe unitate de lungime (de obicei ca unitate de lungime se
mX,sur5, a rezoluliei sistemului. Pentru lezolulia floimloiste5q, tfe'MmTm:),
F:M0,T0e3steseo
obfine valoalea limit5, a lui
',ru

_0.,._i.t_4 I/ _l' \trz
a \s,,)\,. _
_|

Pentlu T-:4kYr .l:1rnmr Il*:2 e\r se oblinc vt:25 cicli/rnm. Aceasta
este valoarea pentru catozii conr.enlionali. Pentlu un fotocatotl din GaAs cu

afinitate negatir-[, penttu electroni, se obfine o frecven!5 spafiali. lirniti
rnult mai mare, v, - 900 cicli/mm, ad.icii este mult mai
rezolutia, sistemului 4.32) conline
mare. IJn tub de imagine cu focalizarc
dc apropiere (fig.
un fotocatod din GaP/GaAs"Pr,-/GaAs : Cs-O ale cllui caract'eristici
sint reprezentate in figura 4.33, pentru sensibililtitea la lLrrninir albri cle
270 pA[n i2El. Ecranul de fosfor este de tip P-20 a,Iuminizat, depus pe
o placir, din fibr[ optic5,. Iubul are ;i un set dc fo:lle pontrn eliminillea fosfo-
rului cncariarceili/mimesimceirdqeciiepacereitelccoercaanIta.eIoIn'r-ea:ti7cceds,thdsYaistrtoyeirmdit,i,r:e\uiztrorlnuitiritano,tanrr.le.Aalocxreimacsai tuniizreivlsa:ulor(aaatr)de,I[reegssttiee-

cle 45
mult,

rea clistribriliei unghiulare a electlonilor carc ies tlin catod. datorit[, t'rigo-
zitd,lii suprafelei acestuia, (b) dirninuarea fluxuhri lurninos datorit5, re-
flexiei pe catod; (c) refle.ria electronilor pe:r,notl.

Fotoca?oC ereostr6 de sticld t 0-'

4 Perete d_e
ceratni cc
I Ecron de
fosfcr
2,5cm

i 'F-l',b7"cemoP-tic-d-4

i_
F-

Iig. 4.32l.iz-aTruebdcdeapimroapgicirnec. cu foca-

Fclicg.lu4n.3g3i.r-nEraiicdieenulnaddcupacnntitcrdu in functie 1 0-3 0,7 q8 0,9 1,0
fotocatc- c,5 0,6 .)., J"'

drrl ('iaP/GaAsrPr-r/GaAs :Cs-O folosit in
tubul de inra3-.ine prezentat in figura ,1.1i2.

4.8. Bmi{.ori de eleetroni seeundari eu afinitate eleetroniel

negativi utiliza{i in foto4ultiplieatori
Ei funclioneazd,, c qi fotocatozii, in dou5, mod.uri: prin reflexie qi
prin transmisie. ln modul de funclionare prin reflexie, electronii primari
pS,trund prin suprafala cu afinitate electronicd, negativS,, ia'r in celilalt
caz prin supla,fala opus5, acesteia. In ambele cuzluri electronii secundari

138

.6F,1

-or(rrrgro,,n]rgrrsrnos'?r7louuq'lreo^us;m;urnKnsr)o8zJ+6rvqlJBaotmyr,luoru:.d[+ardvTzt€rpa€rarl]tdr.ougurapogsrrzutsgaeeoo;lol:Jrsicd.{eguaggnln'oyel:dl!slnIsEunr.errazulu€xnsaa€eulddI€uuurut+rI1s8etux'eIo'nerplrnrIxldtc+ocIlnI€lqrlvoa*IdIJuI'eaorrurxllozsxrtn.coosr]dl1Jl€rop€crtJr'ur6.+errupa:preulJorQrosdorelu1(ic.usrru1de8rrn1xqulo€J"n9OrnoIl6nc9ntzosJ9I€.rtr7(ecuc1gro'ur;'g7du:I

(rg'r) t(z/s-)dxa - Tl #:":

urp alrSor ap ttg g.rupuncos arsrura oaJp€cln(llyodtue;Jrop?upn,rogu.et(l1uerp"rar1aeuurr

tsalulllTquqo,rd) g nc lrflnruur
-rculpu ed (o.rlu*erusrp.Frda) slu(erqpr'lc)uerrI{nu1uao.Jr1ucraolarsea,prdrx{or.rftersu'Bao8c€r.rpeuplucnncpaos,urtuuolJ,:}co1a

aD Inrplunu

(og'r) . gufl : (n)g
ug

OIIDS OS

eurr8trnl op tsolulrun ed r.repuncas Jolruo.rlcola € a.r€.raua8 ap ,uriartng

gv'T
q9'zr

inIulraluI,{

dg$q'DrrJ?JruBJ[cI

9'f nlaqD.L

el€r,raltur
olaun nrluad o6- IS q',n InI a{r.ro{€:\ o}tsp i}rrrs g'? €Iaqt} uI'"gl,g o1sa16-
g.ruurr,rd r18.raua nc Inuo.rlcala ep rie,raua5 r.r'epuncas ruor1ca16 ep "rr, ln.rgurnu
o'rcAunp1c€u1qo'AF-ouo{l1qca1gor€roqso€ar.ruederso!rgrn €a.r€rauo8 na.prliraa}cul'cE}s.rr€lsoooa'loluustrq5,rtai ruraoaplrstan

ri IH"ra}'Brr

(os'r) '$un)irrn:'tI

IaJlsrs rnlnlocrcstsJ v (?g'g1v.r(rur ,urfilaua ep apurdap artsc A- otulo
-'-rouJrnlipcpltolmroutreo1nlo.grqluutSrarcc€lIluee1rl.*reaous]Boorrluoicyuun{olso,p1moucrnt rsl}tsyFr.rdrgae+t}rstitourcgllsinarrcco.\trzloc(payuolo.dCne'opsls.,{r]riI:u€usturp,trrstglJI;1n) ulaorrcutr3rsoco.sd"rut.S{jrl
€ouauras€ o op l€o+lssar.r.croou1ouuorJlucnalaoz€azorlrtzsna.Jrlposa-pBSeIaiauIrJrI8puonllsccTtoscOarJI€Io'ar{p.rro*drnusrl
-,q1eurxo.rde op 6'6
r{1u

uo:dzarlSvJnd(aIrJs1lr;nosduen.r1u orsrrusrrerl u-r KoJz€ecorurzoori?;tc?ucnol;oJo,ar€pcoErrJq€opsotranpcbasrdogts'r(uIStono.r1,tl
u; pzuouor{aun}
rq-eulaoe"drn€o;rlulul3raal d0eT1p=uplfuc1ldai dsKy(+rer€rup+rIsuno4r.Irlu8aet€rdsoarJu?€ar+lrruugrrsq.ogo.r)5gr+eosllsrrurxrouors+nucuua.rloa+rx€uogIoofI,zzr€nuJorIupnogerzipceuorrnuroyurt{8oc.uurenno;l
o.rur rrJolr{ua n.r}uocl 'glrleFau Fcruo.r+aolo o+€llug€ nc tfe;t"rdns ug"rc{ sot

i<i Iri€. 1.ll [. Ilallorttrl clt' t'itiisit'

i sccund{rld potttl'tt Galr lcopcril
I
cu cesiu lu ltlnclie dc cnergia
t:,U i clcc{t'otltlltti Prittillr'

I
i
I

\ 8\)

6A

LA

)0

I ta t2 rd

kev

,B r\4^'
?.e'.'_-F
€c loo
10 15 20 25
qJ Ei, keY

t4

.q

14

(!,

ru
\l
I i/

o
qoa-

I-ri"c. 4.35' -a Raportul dc cmisie sccun-
cl,:ilronilol in Ga'{s'
dari

140

T'I

r-nAIclln'arropucoou.?rrepordsodu'o6rl{g€ngrdroer+pe€uemr.rneaclS11o1€.nrc.nraocp1eelrcn,ride1.drruer1drllunrnuotooslodu}€IuOai +'mruiorpnloloocpx;,ao'msrdnpOlnOgsglnnoccpl opolrrp g
ruogncqd
roun$rql

'IuoJlcalooloJ g e1 puld 6'1 u1 artolgzrnid 'D-IJ
-saJoc atulxBrrr no 1n1us1nd IpurilFul 1n;1cad5 - 'St:'i,

lepuDs eF' rDwnu,t n;ns1nd oawriioul

=t

Qr

J

o

u(rr'it(SSsrsg,asrag1pdnsm'ucatp;cr1l;'etxr*s'umaelJa{lunci)+.rrr€r1darorotx.p+is,ar1?onpscrrCrdorrplolrlorn'ulrouoasurlllplonnoJrdnIurrn{glrr?zppuuld*rcra€|eTllqf{Oeeu'lt;"g:.guerlr'cr6rudtoprnnp{(n1sloo1plq;rooo€uzpluilarioirpnl,rrrtlp{iruruTupsuoaclrnocoacBo}llaAosu.ouauorucro}o+.oruaBn}?iurlncsJ8eoolar-qTrqpr.nlcrlrqlorooilrjro.u.oror}1,].J.pr.u}urrcrls+rpoolurtlsllrorlnno-oIqlrunri?roo}ri,corrrrFor,kl}lJrozugpa;rll
*unslnd n.rluorl alcmilsrp o;tr*ar op r:rnslncl oapurf{.qiood1rrn1rrnnd.rntsus-osJodtr€'o'1lsorlp{'uiTt1p,lol1triurprr
e.ruur r€ur orsrruo
r?uIcrro.rpdapJ€urlrsr o!li:orud'01,6nlclctoTp
u ri n rruo.r,]colo allur aFurlsrp u n.rluacl l .l;r,eur ep
1n+sap Klt?puncas ersruro ap 1;rodu,r un KqrB TS fpourp rLuucl rc ,rilsacarr olso
pr11u gdnp Inun ur,r a.r€o ruo,t.:la{}Io rop,q a.ruolezunclso.roa (alr,insprd) a.riiai ap
ololuuruas o5uilsrp l: n.r+uod'[gg] rcrru orJ KS ,Toqz t-rp 1nduu1 ill alrrirtu,)ng
€c oc€J oc uoot otiJ.reuo ep 1-rn8ir.r It;A;a?uI un (oac11urri"rrau1quru,rlls.irop+IlBrrrlstlzre*ncuTariii?l-rtooaJpl
,royuo;rlcolaoJo; t?orr3.mlunu n.iluotl
-ce1a (g) I

opourp op crru r€ru rJ-(porursnruruuono"pr€sooJc€ouruo1ls.rt)odours,rru(r1o)o:paoftJutlsurur:^rrn?1na1l.oro,rtllelo,rlTTr{llr,,tron )r3p

(6) larut loruo5z rre
qp apourp roorqo
oca.ruoop 's'4ye€Og u1 sdggT IS IS ul estutg\zl v:azd1\t+lgnurilcsrnrlstsroapJoruorlor.cioniy,t]o:niurcdrll,re1,n1inurru,r

-oloJ gI
op Frdurrl +rcop crru rrrtuoisuorgrqul/uur1otrl{cl'Busrccatl0s*pr0nerIu1ri^uonr"ll3ouratzuluoarrJ.rxf1ootJra..urLldaonusJilleocp}opultIoo3n:.}lars.{r+o?oBuctrntiuruurpli1roal1?1.rurE,in1JriD;sr,r.rngr.rrrliililrniirtrlz{,ouuoz.ulraet1}gc)c
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cleci c1 raportul totaldeemisie rnai rnic, ttti sepoate obset'va pulsuldtrt tle un

tnsoirnangileutilrpelfio1ct1a^ottoleinlleiicCtcruou-nI.lceaF-Otootzoai,mucutuilrtniappfluiicnlaitdtaoetreicileec;lteuert:p'telr'oimcnlieacit1d,,i8nneondgsd.a,It^inrd-iLneosGnecqplPuozlit.ei ,uut1fiomlitzoi,a--
ca, numlrd,tori cle fotoni qi au astfel ntari aplica,t,ii in spectroscopie.

-t.9. Emitori de eleetroni eu ealod rcee
Sint joncfiuni p-tt. iu care supra'fe}fa lggiurii p ale trfinitat,e elcctr'o-

nicsnaii,ctife.rieefligecriiugrernaanetifaiarvniptii.lciipiL,p-radoinezitcioctiitallarrlrreuilznudagiirfimeusiziedefairiaeedzcemltdr,dasiriefeuileezescisetitrneoannteileiflcaedecilsn[tz.r\orreEn!g1sil1iotuergn.ereoaSv,.esirtailmuetsneilitainz.tcereiiatngzljitetneicnnmtiati ra'uplii
rnult catotlul lece din siliciu avind in vedere plintre alte avantaje ;i teh-

nologia tlezvoltatl a dispozitivelol tlin siiiciu (fig. a.37). J:'e o plireuli, de

Si-p policristalin

Fig. .1.37. Stt'uctura catodului r.'cr
siliciu cu nlinitatc clt'ctroriicii
sioz din
ncgati\:I.

siliciu cle tip n cu suprafa!,a orienta [, dupd, (100) se creryte un stlat tle SiO-r'
fereastrd', dup[, metodele
in stratul he trioxid rle iiticiu se decupeazd, o
cnnoscute l4], in care se creqte epitaxial un strat cle siliciu p_monocr:ista-
lin cle grosime egaid, cu 2pm. Diametrul ferestlei este in tlomeniul 25 : 250g.m.
Pe sufrafala p-, cit cupi.inde feleastra,- se depune
stratul. activ (cle cxem-
negati't'i. Siliciul cale se
pdl*upuCoi"-Op)epiteenst.tru.rratuol bd'lcinoe-xiadfiensittcaptelicerleiscttraolninic;di, serve;le pcnt,ru contacbul

culoncliunea. vCiedlda,lault ncuointsatcrat talmjoentactlriciu,nci1i e(l.ae5reemgi.upnlueqArul)-1S9pr-e(cauliz0e'a1z%[ SPbri)n:

depuneiea in
pdntru catoziireci clin siliciu s-a oblinut o eficienli (raportul dintre curentul
de 10 %.
de emisie ;i cel de polarizare) In figura 4.38 este reprezentati,

120 2Ag . /e9 609 ;" aQ0 fIu'ignc. li4e.:Jd8.e- Curentul colcctat in

*01roo Iensfqneq d.e co/ecfpr (v) tcnsiunea dc colcctor
pentru catodul rccc din Si cu
Iv 9n afinitatc olectronici negativi.

ao

: 5',0
Y.rc

\f),

20

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oorrxr{o aloBluo] .0I.7

oop-o--u?r?pipFuosooreIlqonnnrIclD?csnsourolluaasaInI"orturls?onJnccrcnqrroEcolnlrruolJsdt(rsBAruKuauuOrJlrlrlrOopaor';Z]agrsar1pcmqp1onou).o.rrJrroclo8\.ur)soloz'acB.1oJrodaco+aloqolEnc1ccorAoecpcrlorol,'lnz|oprucsuup"rrtrounucr{pc1rqn|pgrrrou,rs1sJoru€?ocraauouup?prJonorrrtp'nqnss[JolntcTuru+gluoroBo.l]lglrc€puS1,vuorrKerrnourarol{unuce-rgrruadnxsprr5srurremr8um1oqa/'r+r1l$"lu:urr-azrul,c11'utl"p?noje1lr.scd1q?%rrsrnalisasoi]uru.pr9Japirtra.5rf.6.t'?fr1];ilit?K,lyrlgE}ilz.grr.l,Juvut(p6nua4rn6anszll}

de a lealizavitezf derecombinarelasuprafalit infinitii. Laasemenea'reztltat

se poa,te ajunge qi prin producerea de tlefccte pe suprafala semiconilucto-
miui prin tensionare rneca,nicS, sau alte metocle care clit, na;tere la centre
efective de recombinare; pe suprafala astfel tratatd se depune rnetalul.

BIBLIOGRAFIE

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144

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a)

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b)

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-gI-rwIr.rrtuuet1ll4a(oqgd'(,nBddr_r<€uer,u{rJ),orq?coosluxsaoansaros?p1frqo,nu:aagurl1rroS1popocz1pouue1orunpqt+,s1tso€or1++otssrr)o€u0qeirr<fnKeCcn!ligar,sJ(-g?as.rgt{s,d.o3rt 1urlqgna)lpis(;rf;lorruepo-m.r+nclteonEpFp)uuinoldggcxoereer"urpeloseus.ur:igr;iuurd?S

f€ru ourrrap JolruoJ+cola ur{u.rlueauoc opun rnlnprxo €a+€+€mcoa uI aunrs

:-Lip p. Pcntrn rj.r, 0, banrlao platii,, dezvoltind in selie termenii exponen- ,li
{iali din relalia (5.3) se obline Cr, {llantlit, platri) :1fi e,lL, ;i
:,1

e, (5.4)

'UaP uoft(;)
.c.sle capacitaiea, pe unitatea cle arie, a structurii ln coPclilii d.e band5, plat[-
,Q" din'relalin (ir.3) este sarcina spalialti din semiconcluctor,care este ega15,
.i,1 sarcina'spalialir, clin metal. Distribulia
sarcinii spaliale in strucbura
1'1OS iclealil este reprezentatft in figula r].?. Xn cazul stratului de acumulare

l(x )

Qy

Fis. r.? _ .Disrrib,rria,;li"i:l:';:l:illH.(,',iii,:iJi,lili,:0,::,:r'" regim de acu-

"Q, f=igrQi?",Su.6n"dce., lQa't,eenssiieunsearnceingaaativcui mrnuallactic,apinacsitatrteaata. ,rA_qeavacluomare-ccooonllsstearnvti,i
nri
gtiitaetselernegaareld,c1ceugcoatrpuarci icbaapteaacitoaxteida.uhrlrifi,erCeon,l{iae-lgXar^Cg2ceesfitiendmaarceuminuclaotm5,poarcaaline-
cu Co. Cu scfitlerea tensiunii negativeinvaloare absolut5, qi trecerea la ten-
siunipozitive apare;i se dezvolt* stratuldedefiexie care aclioneazd, ca^un
,dielec?ric in seiie cu oxirlul qi capacitatea total5, a stmcturii scad,e pini,
.:ae'{-t,sinnteeg'esegi;aeo15c,voacnulcoeasnraetrrcarilnniaainiidrmninfp,,su, trCriati-t,.ulillpogdrceia-dcnecafe-lepsxtopieaarlQeiaailoi:i.,nQriz0Nar.ts:eW1q!.ii1(-l-!irlg_see.sm5tei.c?ogtnr,o)c,sluuimcntedoare
,sbriabuiuide deflexie (nereferim la sarcinapeunitatezr, cle atie). Prin,integrarea
ecualiei P6isson se obline distribulia potenlialului in stratul cle deflexie

: #)',t -(t,1,.- (5.5)

unde , qNoVz

v., tt,
-

t1easu1tide,dp1LofitJgea.nr5lci.a?lnlu)i.,trisnlpaaasc{uieaipal5srat,dfd,a.i!iin[t,uscaealmireei,cinocdnaicdpXaucccittuoarrtbeeaasretpeaedtloanttlaStal'Xtdeeaabeedxnpezreailsoriirea cle supra-
a stratu-

c""w:-"" . (5.6)

148

6?T

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Jolr.ro+K+Jnd urzr4rp (a) I .roqonpuoc$uas-rc+vIozt e{eg"rolur tsI o+€zrlr3col K+vJ
-u"rdns op Joir.r'g+s lruporu.ro+ur ur"rd Ea;t€urquroce.r 1i ta.rwauaF (q) l ers.re,rur
op rnln+€r+s € o+E+rurcaa €+tsTpour urp arxolJep ap rnln+€.r+s lruorJo+ul ur
EurcJ€s op rolrro+g+.rnd uo;eulqurooor-€ar€laueF (u) : [1];ro1u-ap erfeurqruoc
nBS oruslu€cour or.lrour1tsr;oro+ugrururJrnrJuorplfpFn.udn-'Jpqlxuor,rodparunnlnrs?.uro,ra?rsrr,usop1uIn,l?rcBuJdg€sc urp
op a;rud
-sm IS e.rude g.od u Klts+o+ uelullcurluc rrunrsuo+ u al€olria t3+rurnu€ o q op Kt€p
o+so rnlnuro+sls
rS pq

qF-€IUI.'I+eEorA1r.IurnelIoUqdeUgrIu.rrraolSegdrr'J(c'6E'rug?rI)Jorelrlons+qatrsrJodldxuaoarcosJproluafllortrplsoJpo€oaIn"rrr1lrt€?oJo+lptssaprror+rrpt€?JEBlsr+rrscc€r.olrcuJn,sr:..prcr{-lu{ eorntlaln1aou";rrr;aisl'psesrs.ugoquf
-€IJtsa Inluuruos I.rKruJn otruocl nu elsJo^ur op In+€J?-s uq) uulc.r,lls p,fua.r.ca.r3
fTf++SII€€tsuouIt)El pnB'f'@nIaa1,ru1c0na0"lsrTyuapogspea?opcfrrrerrl{irp€uluorrc"rugtrd{uuuoarcl{c.cauu.{nquJauep€puzeupca{lueouyprogoslrursqrJaaz-sv,t.o.luo+rpsoorapr?}suuoa"rugtan,r{iiutu-aaa,,"urraoa;urryr;
'g'g ulnfir;ad p,r.rasqo os urnc e"&V (g'S'3rg) a11uui a{ue,tco;lg 'ritl grlrssqo os arut

(a's) -'n ( * ) ''r : "rYc

K+Irrry oJ't?o{€i. o aseul:},t3 ua:1e+lctdBc riuil}srra+ E c.rl3olu,t u?>^Eec€ lt?rl

(s'g) 3:-r'sr'hl'tzu ' th ",

oJsprqcsop ap nu.c Su"rcl ap sunrsuo1 o.triaulnu as rS dr1 nJ uzuo+ou as earu;o1ncl
Ersro,t'ur o;rudta eJsJ tsI pJn+ort-r+s ad g1,t: qdu rounrsuo,1, .F+,squrrqcsar{ putu
orarrdx.raoplJllieoapa.rroldEprlrIJnror+u+Bnts.ripqsus.opu+rrxproir'ua.)p.rtlulIenn?usui+J.ua+orssc,arrodrr,!+ueplaeo;acp1o*Ineut.n?rrcJtt+rrrlsa3+u'iraip,pr,rr1ironuslndno1Jdua"rsneL,.t--.lrpo.grpd.r{?np,1rr
-FUEJ
a+rrBoJ
-cnJ+s

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,ropuo"r+JoTa t:r{u.l,1uoouoo pulc : ,urru,rai;nrl orsJoirrr op urjrprrot elurza.rda.r
- : qEpoK'F-trl+&{rxI1trtuo'nsi1(uAl6nonrtu'u*lu9uu€o'uFrrroltox€lte+0aura1)liuJr1dJra"'*iB.Jpuipeacaooslspulupunaa€o;cqsIanl'dc3ol+pt-tuurulstxelJlconraF+uJrl;saJtrn^?mouaasopr"sl14dsuItluoooJeropE+urrer^xirculrenu.Jatrl1"JudS.unrosteou)+psloEriranrfcJear,J?4rpt€zawsuJzrcann,r1uTaBuc1on{ad.?lupaoleqzreu?dndlJeuscr1a,1.r.ssrlx?reqao,s"EprralizotrIcoo,rnrasu.dnrrru.cuul\nn-cculuiu.sr$m'5;rQa'lrJs"aiuufuu(t(rog'tIrcg1n?..r€.arInFurp€lq1rg?1a??oo€n)1..J.tbr"rur"1J-?(ofcssollle,lueiue€+t-tn,Ld-tr
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##*'lL:(r'q) oalc

ocl rr"rnlcn-r+s € TieXo+ ersa"rdxe {o1le ep €a?ql+run
uelulrcedul n"rluad aur{qo os sns rtsui ap opr{rio;
'('11/if ""] -- fttlaAue) urp
rrurc,rts rIJElJasuorea8al a.ropar ui pulAr-

de inc6rcare-descd,rcare a stratului de inversie asociali acestor meca'nisme
sint destul de mici, astfel c5, timpul de realizare a incS,rcd,rii sag desc*rcilrii,
ci,,, €ste mare2 de orclinul" miimilor gi sutimilor de secundd,. Prin un'illal'e,
stratul de inversie poate s5, umi,reascS, un semnal variabil de frecr.-tn{,5, f
farpeclicveant lpeeiosatnserc. tftnrira, cneausmtSa, isidtaucadl'ieJ<o1v/a"uri,a,l,iecoantdei!n,iseiucnairieceosntceluicnedeiaplvinaitliir:,llilatr'
sarcinii din stratul cle inversie qi prin urmare capacitatea m5surat5, cstc ceir
a, stra,tului cle oxid, a$a cum am amintitmai sus. Pentru ./(1/"i".";-rilrcina,
din stratul de inversiune nu poate tlrm['ri semnalul de frecvenld /, ln schimb
sarcina clin stratul de deflexie poate urm5,ri sernnalul variabil si r,llpaci-
tatea mXsuratS, este cla,td de ecualia (5.9). Menliond,m cd, in cazul striatrLlui
de acurnulare sau de deflexie incH,rcarea nsi clescdrcarea cu salcinS, gs fa1a,r prin
deplasarea purtzitorilor majoritari intr-un timp egai cu timpul cp c1e rela-
xare ilielectricii care are valoare rnpu:lt 5m0a,icmrnictsi,edeocbitlinr,enu.roD:e
eren:lplu,
pentru siliciu cu rezistivitatea 5.10-12s.

Sarcina clin stratul de acumulare sau de cleflexie poate urrnX,ri senrnalul
variabil la o frecven\il, f <1"1q, frecvenlii, care este de orclinul GIIz ;i rXriar

mai mare. Un exemplu de clependen![ capacitate-tensiune pentru o si'r'uc-
-l[r:16re,''*- a
tur5, MOS ideali, cu siliciu de tsiptraptcuuluciondceenotxriaclliail acceptorilor cel tlin figura'
grosimi ale constituie
pentru diverse
5ic.l8ea[l2e,].uInndfieg?ureast5e.9reezsitseterenplareczleenvtoaltumcircausiteurnl ieccohnidvuacletonrtualuli.stirnucitnucrhiieiMerOeaS,
acestui paragraf notSm cd, deqi sarcina clin stratul de inversie al str-irrturii
IIOS nu poate urrnXri semnaluL de inaltd, frecvenli aplicat pe poar,xrii,, in
eazttltranzistomiui cu efect de cimp cle suprafa!il regiunea surs5,, puternic
d.opat[, este in contact direct cu stratul d.e inversie in condi.tii norn:lille de
Iucru. Astfel,regiunea sursd, poate sd, alimentezerapid stratul de inversic cu
purtd,tori minoritari si tranzistorul IIOS cu efect c1e cimp poate func{iona
ta inalt5, frecvenfd,. ln realitate caracteristicile stlucturiil"iOs sintrliferite

iCOCA QV

-2 I
v,v
* too
Fig. 5.8 * C(Y) pentru structura MOS idea]6.
I
150
i

T%"

I
t"

q€.-n

1

t

d

Fecighi.va5l.e9n. t-d Schema

a struc-
turii I'IOS idealc.