pset 5 - University of California, Berkeley EE230 - Solid...

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University of California, Berkeley EE230 - Solid State Electronics Prof. J. Bokor pset 5.fm PROBLEM SET 5 (Due Thursday, May 1, 2008) 1. (Lundstrom 2.6) For alloys of compound semiconductors such as Al x Ga 1-x As, microscopic fluctuations in the alloy composition, x, produce perturbations in the conduction and valence band edges. The scattering rate for alloy scattering is: where N is the concentration of atoms, Ω is a normalization volume, and ( χ is the electron affinity). a) Explain why the alloy scattering rate vanishes at x=0 and x=1. b) Derive an expression for τ m (p) for alloy scattering. 2. (Lundstrom 2.9) Compute and compare the momentum relaxation times due to ionized impurity scattering under the following circumstances: a) Find 1/ τ m for electrons with the thermal average energy E=3kT L /2 in GaAs doped at N D =10 18 cm -3 . Assume T L = 300K. Compare L D with b max and discuss whether the screened (Brooks-Herring) or unscreened (Conwell-Weisskopf) theory is most appropriate.
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This note was uploaded on 08/01/2008 for the course EE 230 taught by Professor Bokor during the Spring '08 term at University of California, Berkeley.

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pset 5 - University of California, Berkeley EE230 - Solid...

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