06++Drift+and+Diffusion

06++Drift+and+Diffusion - Review: Important Equations n, p...

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Review: Important Equations n, p may be determined from Fermi energy, or Fermi energy may be determined from n, p = kT E E N p f V V exp = kT E E N n C f C exp = kT E E n p f i i exp = kT E E n n i f i exp = C f C N n kT E E ln = V V f N p kT E E ln = i D i i f n N kT n n kT E E ln ln = i A i f i n N kT n p kT E E ln ln
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EECS 320 Drift Current
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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 =
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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
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Drift Current Drift current due to electrons and holes ρ σ E = = drift J JA L A L I V R = = = ) ( ) ( ) ( drift p drift n drift J J J + =
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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
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This note was uploaded on 08/09/2011 for the course EE 320 taught by Professor Zhongzhaohui during the Summer '11 term at Shanghai Jiao Tong University.

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06++Drift+and+Diffusion - Review: Important Equations n, p...

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