06_Drift+_+Mobility

06_Drift+_+Mobility - Carrier Drift and Mobility What are...

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EECS-320, L.J. Guo 1 Carrier Drift and Mobility What are the primary types of carrier action in a semiconductor? Drift, diffusion, recombination-generation How do carrier velocity depend on E-field? What is carrier mobility? What are the key parameters that determine the mobility? What are the main scattering mechanisms in semiconductors, and their temperature dependence? How to represent E-field in band diagram?
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EECS-320, L.J. Guo 2 Carrier Motion in Semiconductors V th typically ~10 7 cm/s for most semiconductors! Under an electric field, carriers acquire an additional drift velocity v d between consecutive scattering events, which can be determined from dn va t = *2 13 22 Ct h E Em vk T −= = “free” carriers have constant thermal motion, and move randomly with zero net displacement
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EECS-320, L.J. Guo 3 Drift Velocity & Mobility Carriers are accelerated by electric field E Carriers are scattered from crystal imperfections, with mean scattering time Average velocity obtained between scattering events is v drift Mobility relates v drift and electric field t How do electrons and holes respond to an applied electric field? * drift q va t t m μ == = E E * q a m = E 3 drift v = E * * n n e p p h qt m m = = Note: * 1 n m μ∝ v E Ε = μ drift v
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EECS-320, L.J. Guo Example 4 Si with N D = 3×10 16 cm -3 at 300 K
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EECS-320, L.J. Guo Mobility
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06_Drift+_+Mobility - Carrier Drift and Mobility What are...

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