EE506 Semiconductor Physics Homework Assignment #6 Prof. Steve Cronin Due November 22, 2011 Optical Properties: 1.) a. At what carrier density does Si with a mobility of 1450cm 2 /V ∙s and ε core =12 begin to have a plasma frequency? b. Using the results in (a.), write an expression for the free carrier contribution to ε(ω) . c. Plot the real and imaginary components of ε(ω) . d. Find the plasma frequency for doped silicon with n =10 18 electrons/cm 3 , in units of eV. 2.) a. Determine the absorption coefficient due to free carrier absorption at a temperature of 300K and a free space wavelength of 0.9 µ m for a partially compensated GaAs samples with N d =2 x 10 18 /cm 3 and N a =1 x 10 18 /cm 3 for the donor and acceptor concentrations. Assume a mobility of µ =3000cm 2 /V ∙s, ε core =15, and m * =0.065 for GaAs. b. Where does the Fermi energy in (a) lie? c. For heavily doped GaAs the Fermi energy gets pushed way into the band. In order to excite an electron into the conduction band, one must go away from
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