09 - Drift and Diffusion

# 09 - Drift and Diffusion - EECS 320 Drift and Diffusion...

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Unformatted text preview: EECS 320 Drift and Diffusion Current J. Phillips EECS 320 Thermal Motion Of Carriers Electrons move randomly in crystal with zero net displacement This is the thermal motion of carriers V th typically ~10 7 cm/s for most semiconductors! J. Phillips EECS 320 Application Of Electric Field Electrons/holes respond to electric field Ε = µ drift v * m qE v drift τ = • Note that carriers are in motion without electric field (thermal energy) • Carriers are accelerated by electric field • Carriers scatter from crystal imperfections • Average velocity obtained between scattering (vdrift) J. Phillips EECS 320 Drift Current Drift current due to electrons and holes ρ σ E E J drift = = JA EL A L I V R = = = ρ ) ( ) ( ) ( drift p drift n drift J J J + = J. Phillips EECS 320 Conductivity and Mobility Define mobility: proportionality between v drift and E, represents carrier scattering dp dn drift qpv qnv E J + = = σ E qpv qnv dp dn + = σ E v dn n − = µ E v dp p = µ Conductivity depends on both carrier density and mobility p n qp qn µ µ σ + =...
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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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09 - Drift and Diffusion - EECS 320 Drift and Diffusion...

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