Lecture #13. Diode Current due to Generation

Transcription

1 Lecture #13 Juctos OUTLINE reverse bas curret devatos from deal behavor small-sgal model Readg: Chaters 6. & 7 EE13 Lecture 13, Slde 1 Dode Curret due to Geerato If a electro-hole ar s geerated (e.g. by lght) the deleto rego of a Schottky dode or dode, the bult- electrc feld wll swee the geerated carrers out, resultg a addtoal comoet of curret. EE13 Lecture 13, Slde

2 Revew: Curret Flow Log-Base Dode Uder forward bas (V > ): Holes are suled (from the exteral crcut) through the -sde ohmc cotact Some of these recombe wth jected electros; the rest are jected to the -sde Electros are suled (from the exteral crcut) through the -sde ohmc cotact Some of these recombe wth jected holes; the rest are jected to the -sde EE13 Lecture 13, Slde 3 Revew: Curret Flow Short-Base Dode Uder forward bas (V > ): Holes are suled (from the exteral crcut) through the -sde ohmc cotact If the -sde s short (W P << L ), ~all of the holes are jected to the -sde, ad recombe wth electros at the -sde ohmc cotact Electros are suled (from the exteral crcut) through the -sde ohmc cotact If the -sde s short (W N << L ), ~all of the electros are jected to the -sde, ad recombe wth holes at the -sde ohmc cotact EE13 Lecture 13, Slde 4

3 Reverse Bas Curret Cosder a reverse-based (V <) jucto: morty carrer cocetrato -x x x Deleto of morty carrers at edges of deleto rego The oly curret whch flows s due to drft of morty carrers across the jucto. Ths curret s fed by dffuso of morty carrers toward jucto (suled by thermal geerato). EE13 Lecture 13, Slde 5 lteratve Dervato of Formula for I Deleto aroxmato : excess morty carrer cocetrato x I reresets the rate at whch carrers are geerated wth a dffuso legth of the deleto rego / N -LN-x x -x t t / N EE13 Lecture 13, Slde 6 D x x x + L -x I x P ql N / N + ql P / N D

4 Devatos from the Ideal I-V Behavor EE13 Lecture 13, Slde 7 Effect of R-G Deleto Rego The et geerato rate s gve by t t where E T 1 e ( + ) + ( + ) ( E E )/ kt ad tra - state eergy level T ( E E )/ kt R-G the deleto rego cotrbutes a addtoal comoet of dode curret I R-G x I R G q dx x t 1 1 R G 1 e T EE13 Lecture 13, Slde 8

5 For reverse bas greater tha several kt/q, qw where I R G + I I EE13 Lecture 13, Slde 9 For forward bases, I R G qwe qv / kt I I EE13 Lecture 13, Slde 1

6 Effect of Seres Resstace EE13 Lecture 13, Slde 11 Hgh-Level Ijecto Effect s V creases, the sde of the jucto whch s more lghtly doed wll evetually reach HLI: > ( o + jucto) or > o ( + jucto) sgfcat gradet majorty-carrer rofle Majorty-carrer dffuso curret reduces the dode curret from the deal EE13 Lecture 13, Slde 1

7 Revew: Charge Storage -Dode EE13 Lecture 13, Slde 13 Small-Sgal Model of the Dode Small sgal equvalet crcut: v R1/G C Gv + C dv dt Small-sgal coductace : G 1 R di d I ( e qv / kt 1) d I e qv / kt G q kt I e qv / kt I DC / kt q EE13 Lecture 13, Slde 14

8 tyes of caactace assocated wth a jucto: 1. C de deleto caactace. C D dffuso caactace (due to varato of stored morty charge the quas-eutral regos) For a oe-sded + jucto, Q P >> Q N so Q Q P + Q N Q P : C dq di G D I DC kt / q EE13 Lecture 13, Slde 15 Deleto Caactace coductor C de W sulator dq de ε s W coductor What are three ways to reduce C de? EE13 Lecture 13, Slde 16

9 Total -Jucto Caactace EE13 Lecture 13, Slde 17 C de -vs.-v (Reverse Bas) 1 W ( Vb V ) C ε s qε N de S EE13 Lecture 13, Slde 18

10 If the sloe of the (1/C de ) vs. V characterstc s x1 3 F - V -1, the tercet s.84v, ad s 1 µm, fd the lghter ad heaver dog cocetratos N l ad N h. Soluto: N l /( sloe qε /( cm 3 s ) Examle cm ) V b kt NhNl l q N h qv b kt e e N 6 1 l cm 15 EE13 Lecture 13, Slde 19