Chp6. pn Junction Diode: I-V Characteristics I

Transcription

1 147 C6. uctio Diod: I-V Caractristics I

2 6.1. THE IDEAL DIODE EQUATION Qualitativ Drivatio 148 Figur rfrc: Smicoductor Dvic Fudamtals Robrt F. Pirrt, Addiso-Wsly Publicig Comay

3 149 Figur 6.1 juctio rgy bad diagram, carrir distributios, ad carrir activity i t ar viciity of t dltio udr (a) quilibrium (V A =0), (b) forward bias, ad (c) rvrs bias coditios. (d) Dducd form of t I-V caractristic. Figur rfrc: Smicoductor Dvic Fudamtals Robrt F. Pirrt, Addiso-Wsly Publicig Comay

4 150 at quil., ( ) = ( ) at forward bias, V A > 0 ( ) >> ( ) t barrir igt dcrass liarly (V bi V A ) t carrir coctratio vary otially. t umbr of carrirs tat av sufficit rgy to surmout t ottial barrir gos u otially wit V A I qv A/kT

5 151 at rvrs bias, V A < 0 ( ) < ( ) t barrir igt icrass. t umbr of lctros o -ty sid tat ca surmout t rgy barrir dcrass raidly. I -I 0 qv A /kt I = I 0 ( - 1)

6 15 Wat as to t ijctd carrirs? a carg build-u isid dvic? o! T total currt troug t diod must b costat wit ositio isid t diod. Figur 6. Comosit rgy-bad/circuit diagram rovidig a ovrall viw of carrir activity isid a rvrs-biasd juctio diod. T caacitor-lik lats at t outr ds of t rgy bad diagram scmatically rrst t omic cotacts to t diod. Figur rfrc: Smicoductor Dvic Fudamtals Robrt F. Pirrt, Addiso-Wsly Publicig Comay

7 Quatitativ Solutio Stratgy Gral Cosidratios Basic Assumtios (1) Stady stat () No dgratly dod st juctio (3) 1 D (4) Low lvl ijctio (5) No otr rocss ta drift, diffusio, ad trmal R/G. G L = 0

8 154 ( ) q ( ) qd q qd d d d d T total currt dsity is costat trougout t diod, but t lctro ad ol comots vary wit ositio. (), (), () cssary!

9 155 Miority carrir diffusio quatios (ξ 0, low-lvl ijctio) may b alid to t quasiutral rgios of t diod Figur 6.3 Diod lctrostatic rgios. Fig W do ot tat t coditios rquird for t us of t miority carrir diffusio quatios, icludig 0 ad low-lvl ijctio, ar satisfid i t quasiutral rgios of t diod. Figur rfrc: Smicoductor Dvic Fudamtals Robrt F. Pirrt, Addiso-Wsly Publicig Comay

10 Sic Quasiutral Rgio Cosidratios Stady-stat, G L = 0, N P D D N P d d d d d d0 0, d d qd N qd P d 0 d d d 0

11 W ca obtai o -ty sid o -ty sid 157 t ow ca w gt t total currt? Dltio Rgio Cosidratios d dt 1 q d dt trmal RG d otr rocsss Stady-stat, 0, o otr rocsss, 1-D, dt 0 1 q d d d dt trmal RG ad 0 1 q d d d dt trmal RG

12 Assum, trmal R-G gligibl i dltio rgio., ar costats iddt of ositio i dltio rgio! d d d d ) ( ) (

13 159 Boudary Coditio two boudary coditios cssary for -ty ad -ty sid, rsctivly. At t omic cotacts, log-bas diod. Assumd. cotacts at = ± ( - ) = 0 ( + ) = 0

14 160 P N (-cotact) (- ) ( ) (-cotact) (a) E F F F E c E F E i E v - (b) Figur 6.4 Boudary-coditio rlatd cosidratios. (a) Boudary ositios ad rquird valus. (b) Aroimat variatio of t quasi-frmi lvls wit ositio isid a forward-biasd diod. Figur rfrc: Smicoductor Dvic Fudamtals Robrt F. Pirrt, Addiso-Wsly Publicig Comay

15 At t dltio rgio dgs quasi-frmi lvl formalism, 161 i ( E F E )/ kt i i ( E E i F )/ kt i ( E F E F )/ kt i qv A / kt law of juctio At t -ty dg of t dltio rgio, i qv A N / kt A

16 i / kt qv / kt 1 i A N A N qv A A 16 Similarly, qv / kt 1 i A N Gam Pla Summary (1) Solv t miority carrir diffusio quatios wit B.C. ad gt Δ ad Δ () Gt, (3) Gt (- ) ad ( ), ad add t two to gt total D