Lec09 Drift and Diffusion

Lec09 Drift and - EECS 320 Drift and Diffusion Current Thermal Motion Of Carriers Electrons move randomly in crystal with zero net displacement

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Unformatted text preview: EECS 320 Drift and Diffusion Current Thermal Motion Of Carriers Electrons move randomly in crystal with zero net displacement This is the thermal motion of carriers (In 3D, average K.E. = 3/2 kT) typically ~10 7 cm/s (200000 mph) for most semiconductors! * / 3 m kT V th = Application Of Electric Field Application of electric field will result in a net displacement E E µ = drift v E • Carriers are accelerated by electric field • Velocity randomize due to scattering at scattering centers (Average time between scattering, τ) • Average velocity v drift • Mobility relates v drift and electric field Drift Current Drift current due to electrons and holes ρ σ E E = = drift J JA L A L I V R E = = = ρ ) ( ) ( ) ( drift p drift n drift J J J + = Conductivity and Mobility Define mobility: proportionality between v drift and E, represents carrier scattering dp dn drift qpv qnv J + = = E σ v E µ depends on mean time between scattering τ and m * * m q v drift τ E = * m q τ µ = E µ = drift v E dp p v = µ E dn n v − = µ E dp dn qpv qnv + = σ Conductivity depends on both carrier density and mobility p n qp qn µ µ σ + = Mobility...
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This note was uploaded on 01/31/2011 for the course EECS 320 taught by Professor Philips during the Spring '06 term at University of Michigan.

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Lec09 Drift and - EECS 320 Drift and Diffusion Current Thermal Motion Of Carriers Electrons move randomly in crystal with zero net displacement

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