EE"232"Lightwave"Devices Lecture"16:"p7i7n"Photodiodes"and" Photoconductors"

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Hortense Gwendolyn Franklin
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1 EE"232"Lgwav"Dvcs Lcur"16:"p77n"Pooos"an" Pooconucors" Rang:"Cuang,"Cap."15"(2 n E) Insrucor:"Mng"C."Wu Unvrsy"of"Calforna,"Brkly Elcrcal"Engnrng"an"Compur"Scncs"Dp. EE232$Lcur$16-1

2 Rvrs"bas%p""n%juncon Mos%of%%volag%rop% across%%"rgon,%% man%absorpon%rgon P""n%Pooo P N Hg%fl%sparas% poognra%lcron%an% ol Larg%bangap%marals%ar% us%for%p%an%n%f%possbl Fas%rspons Ec 1 q Ev q 2 Low%nos F q 3 No%gan%(quanum%ffcncy% <%1%) 2 4 " 1 7 1" 1 7 1" 1 7 2" 1 7 x EE232$Lcur$16-2

3 I"V$Curv kbt Dark currn: I = I ( $ 1) qv I " q Poocurrn: Ip = Pop # $ Quanum ffcncy: " = " (1 $ R)(1 $ ) V kbt Toal currn: I = I ( $ 1) + I qv p I p1 I p2 Loa$Ln$for$Basng$$PD EE232$Lcur$16-3

4 Absorpon*Coffcn Lg*nnsy*cays* xponnally*n*smconucor: I( x) = I " x Drc*bangap*smconucor* as*a*sarp*absorpon*g S*absorbs*poons*w* v*>*e g =*1.1*V,*bu** absorpon*coffcn*s*small Suffcn*for*CCD A*gr*nrgy*(~*3*V),* absorpon*coffcn*of*s* bcoms*larg*agan,*u*o* rc*bangap*ranson*o* gr*cb EE232$Lcur$16-4

5 Two$Typs$of$p**n$Pooos L Surfac-Illumna p--n # " = " (1# R)(1 # ) " : nrnal quanum ffcncy R : rflcvy : absorpon layr cknss Wavgu p--n #$ L " = " (1# R)(1 # ) " : nrnal quanum ffcncy R : rflcvy $ : confnmn facor L : lng of wavgu PD EE232$Lcur$16-5

6 Ramo s'torm T currn caus n xrnal crcu by a movng carg q movng a a volocy v ( ) n a paralll pla w a sparaon of an a volag bas of V s qv() () = A Proof: Work on on carg: W = Forc Dsplacmn V = qex = q x Work prov by powr supply: W = () V " V () V = q x q x qv() () = = EE232$Lcur$16-6

7 Rspons'of'On'Poognra' Elcron4Hol'Par qv / () = () + () () P N qv / () Tm EE232$Lcur$16-7 x Hol Trajcory Elcron Trajcory v x x v Toal carg gnra: $ $ Q = () + () qv " x qv x v v = + = On absorb poon Tm on carg c q #

8 Trans(Tm () = () + () () P N () Many(lcron2ol(pars gnra v v Tm Elcron currn ns wn las lcron gnra nar P-s racs N-lcro: = v Hol currn ns wn las ol gnra nar N-s racs P-lcro: = v Hol s usually slowr " A consrvav sma of rans m: = v EE232$Lcur$16-8

9 Toal&Rspons&Tm&of&p//n (1) RC m: A " RC = RC = R ( A : ara of p--n) (2) Trans m: " Toal rspons m: " = " + " f = 3B v RC 1 $ 2#" Absorpon layr cknss for opmum frquncy rspons: R A " = " RC + " = + v $ R A%$ % " & 2 ' (' ( ) *) v * 1 1 v f3b +, = f3 B,max 2#" 4# R A Opmum banw occurs wn R A = opmum v = R Av EE232$Lcur$16-9

10 Mor%Rgorous%Analyss%of p22n%rspons%tm 2 Small-sgnal analyss: assum npu lg s moula a frquncy, poocurrn s proporonal o 2 #" $ sn 1 % & 2 ()) ' ( j RC #" $ % & ' 2 ( T frs rm s sngl-pol rspons from RC, wl scon rm s pas lay u o rans m rspons. RC #( ( ) ) 2 2' log$ H1 f Trans Tm Toal % & #( ( ) ) 2 2' log$ H2 f " 2 " % & #( ( ) ) 2 2' log$ H3 f 2 " 2 " % & 2 f f " 2 EE232$Lcur$16-1 " f

11 Exampl: f RC 3B = 14.4 ps = 2 ps EE232$Lcur$16-11 Comparson*of*Numrc*Exampls 1 1 = = 4.6 GHz 2" + RC 2 $ # % sn 1 & ' 2 ()* ( ) = H( #) 2 1+ j# RC $ # % & ' ( 2 ) 1 Solvng H( #) =, f3b = 9.7 GHz 2 T scrpancy s smallr wn RC omnas, an largr wn rans m omnas. (Trans m rspons as a sarp rop-off). RC #( ( ) ) 2 2' log$ H1 f Trans Tm Toal % & #( ( ) ) 2 2' log$ H2 f 2 " 2 " % & #( ( ) ) 2 2' log$ H3 f 2 " 2 " % & 2 " 2 " f f f

12 Banw)Effcncy/Prouc (1) For surfac-llumna p--n (assum AR coang: R=%), n xrm of n absorbng layr an rans-m-omna rspons: $ " = " (1 $ ) %" (1 $ (1 $ )) = " 1 v f3b % 2# ( 1 v ) " v Banw-ffcncy prouc: f3b *" % +,(" ) = - 2#. 2# (2) On or an, ffcncy of wavgu p--n s $' L " = " (1 $ ) %"' L 1 RC-lm banw: f3b % 2# R& Lw ( 1 ) Banw-ffcncy prouc: f3b *" % +,(" ' L) = - 2# R& Lw. / In gnral, r s a banw-ffcncy ra-off " ' 2# R& w EE232$Lcur$16-12

13 Pooconucors Dark currn: J = σ E = ( n qµ n + p qµ ) p E + 5 x Ara = w L Equvaln2Crcu Lg llumnaon gnra lcron-ol pars, ncrasng conucvy: δn = G δn τ n Say sa: / --> δn = G τ n ΔJ = δn q ( µ n + µ ) p E EE232$Lcur$16-13 Pooconucor rqurs bo conacs o b Omc an smconucor opng yp o b sam.

14 Poocarrr*Gnraon*Ra Lg Innsy # " x + / x Ara = w L Pop (1 R) x (1" " ) Pop 1 1 G = " : poocarrr gnraon ra [ ] # 3 lw cm s $ " = " (1 $ R)(1 $ ) R : rflcvy of pooconucor surfac : absorpon coffcn : absorpon lng $ : fracon of lg rmans afr absorpon lng EE232$Lcur$16-14

15 Pooconucv,Gan ( )( µ µ ) $ I = lw$ J = lw G q + E n n p % Pop 1 & $ I = lw' " ( ) n( q µ n + µ p E ) # lw * Pop 1 q 1 $ I + " q( µ E) = " P v # # = : rans m v I n % q &% & " P ) *) * n $ = ' op (' ( # n n op n n Poocurrn Pooconucv Gan EE232$Lcur$16-15

16 Analogy(o(Currn(Gan(n(Bpolar( Transsor Currn gan n bpolar ranssor: E B C I = I C B T currn gan can also b xprss as " rb = " " : rans m " rb : carrr rcombnaon lfm n bas EE232$Lcur$16-16

17 Frquncy)of)Pooconucors N = η P op 1 ω lw N τ n Small sgnal rspons: N = N + N 1 jω jωn 1 = η P 1 1 ω lw N 1 τ n Pooconucv)Rspons)(B) n / = 1, n / = 1, n / = 1 n / = 1 / = 1 ηp N 1 = 1 1 n ω ( lw) jω +1/ τ n I 1 = J 1 lw = ( N 1 qv n )lw I 1 " = ηq %" $ ' τ % n 1 P 1 # ω $ &# τ ' & jωτ n +1 = ( DC Quanum Effcncy) ( Pooconucv Gan) ( Normalz Frquncy Rspons) Frquncy)(Hz) EE232$Lcur$16-17

EE 232 Lightwave Devices. Photodiodes

EE 232 Lightwave Devices. Photodiodes EE 3 Lgwav Dvcs Lcur 8: oocoucors a p-- ooos Rag: Cuag, Cap. 4 Isrucor: Mg C. Wu Uvrsy of Calfora, Brkly Elcrcal Egrg a Compur Sccs Dp. EE3 Lcur 8-8. Uvrsy of Calfora oocoucors ω + - x Ara w L Euval Crcu