3.++Semiconductors+Basics

3.++Semiconductors+Basics - MATSCI 302 April 7, 2008 Fermi...

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MATSCI 302 April 7, 2008 Fermi Level Excess Carriers Created by Light Absorption Quasi Fermi Level Drift and Diffusion Light is absorbed outside of the depletion regions. Minority carriers must diffuse to this region. Reading: Chapters 3 and 4 from Streetman’s text.
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Important Equations n 0 p 0 = n i p i = (n i ) 2 For silicon at room temperature, n i = 1.5 x 10 10 cm -3
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At equilibrium: 2 2 so , 0 0 i i n G R G n p n R r = = = = α Recombination (R) and Generation (G)
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Suppose we shine a pulse of light on a semiconductor. How long do the extra carriers live? )] ( )][ ( [ ) ( ) ( 0 0 2 t p p t n n n R G dt t n d dt t dn r i r δ α + + - = - = = 0 0 ) ( ) ( ) ( p n t n t p t n + < < = ) ( ) ( ) ( 0 0 t n p n dt t n d r + - = ) ( ) ( 0 0 t p p p t n n n + = + =
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For a p-type material, 0 0 p n < < lifetime carrier minority 1 ion concentrat carrier excess initial n ; ) ( ) ( ) ( 0 0 0 = = = = = - = - - p e n e n t n t n p dt t n d r n t t p r n r α τ δ Key points: exponential decay 0 1 p ) ( )
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3.++Semiconductors+Basics - MATSCI 302 April 7, 2008 Fermi...

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