Conduction Mechanisms in Semiconductors: Drift and Diffusion Analysis
Explore the conduction mechanisms in semiconductors through drift and diffusion analysis. Understand how carriers move under electric fields and density gradients, and delve into Fick's Law and Einstein's Relationship. Discover the equilibrium conditions and the role of majority and minority carriers in semiconductor conduction.
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EECE 310 - Lecture 11 Prof. Ayman Kayssi
Outline Conduction Mechanisms in Semiconductors 2 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors Drift: Electric field E causes carriers to move with drift velocity v, such that ? = ?, ?? ? ? ???????? ??= ? ? ? = ? ? 2.5 Current density = Charge density velocity J e = J h = J J e + = = = n q J ( + p q q n p = v v q q q n E e h p E h h ) E p n p I ? J = ( ??2) A 3 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors I ? J = ( ??2) A ? = ?? (? ? ? ???) n q = + q p n n 1 ???????????? = ??????????? I ? =? ? ?= ? ? J = A ? ? ? =1 ? ? ? = ? ? ? ? 4 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors Diffusion: Density Gradient dp = J qD Fick s Law: p p dx q= charge of an electron= 1.6 x 10-19 C ??= diffusion constant for holes ?? ??= ???????? ?? ?????????? ?? ? ??? ??????? ?? ? dn = J qD For electrons: e n dx Diffusion constants are related to mobility: Einstein s Relationship D D KT p n = = = V T q p n 5 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors 6 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors N N V = ln A n D V o T 2 i 7 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors At equilibrium: ??????????= ?????? Such that ??????= 0 ??????????is due to majority carriers who can cross over the barrier (few of them). ??????is due to minority carriers who are swept across the depletion region by ? 8 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors V D F D p = + V 2 n I Aq n e I Diffusion i L N L N p D n A I?????= ????? ?????? ??? ??= 0 & ??????= 0 D D p = + 2 I Aq n n Drift i L N L N p D n A V D F D p = + ) 1 V 2 i n ( I Aq n e T Total L N L N p D n A 9 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors Diode Equation: ? ?? 1) with n=1 ??= ?? (? PN Junction Diodes 10 EECE 310 - Fall 2019
Conduction Mechanisms in Semiconductors 11 EECE 310 - Fall 2019
Thank you ! 12 EECE 310 - Fall 2019
