Transcript
PN junction.... Foundation of semi-conductor componentsSemi-conductor:
empty
11 11 11 ILL 33psibe spSi Si Si as
I I l 11 is
empty conduction bandgapto all e areftp.zef µ chemicalpotentialinthevalence band
Otto small eµvalenceband
fraction e 8972kt
of e are in the conductionbandThe same fractionofholes are inthevalenceband
KT is 25mW roomtemperature so thisfractionis verysmall
P type semi-conductorN-type semiconductor
a si MEEEGalliumhasonly3valenceelectrons
and is an electronacceptor
When an electronhops thevacancy hole moves in the
opposite direction in thep typesemi conductor
s PIE'sif I'm'Efer Fam
A phosphorous atomhas 5 valence 71
electrons The extra one can easily M Fbreak loose
P is an electron donor
e can easily move in a n type s c
PN junction: when electrons meets holes
tRandomwalk diffusion of e and holes
I
tI K
depletionregimenegatively changed on The left sidepositive charged on theright side
Depletonregime hasveryfewmobilechange carriers
Whenequilibrium is established Diffusionbalancedbyelectricalforce
Idiffusion Idrift jelectron
energy xfburrier topreventfurtherdiffusion
n0
barriertopreventholediffusion
Forward biased: depletion regime narrowed Reverse bias: depletion regime widened
47ftl K depletion
efIfyq Er µIdiffusion Idrift T
V
Emdemand
EFoLIdiffusion 7drift
Current through a biased diode:
A simplifiedderivation
Jdiffusion Idrift I Iholenee'M T jdriftdm me eM T j drift
Notethat je o when to NeeM II driftje jdriftCe l
I Io e T l
A
whathappened here
I
Avalanche regime
vtdepletion
e
po d
spontaneous e holepaingenerationor photon induced E hole pairin photodiodes
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