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20101ee2_1_HW3

20101ee2_1_HW3 - carriers are created uniformly everywhere...

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Physics for Electrical Engineers Prof. B. Jalali EE 2 Homework #3 Due: Feb. 25 th , 2010 1. Given the mobility of electrons as 1200 cm 2 /V-sec, determine the resistivity of a n-type silicon with 10 16 cm -3 donor atoms. If the effective mass is 0.26m o , calculate the mean (average) scattering time. 2. The hole density in a n-type semiconductor varies as A exp(-x/L p ). Write down the expression for the electric current due to hole diffusion in terms of the hole diffusion constant. How is the current changing with distance, and why? Under what circumstances will the diffusion current be constant? 3. A piece of intrinsic silicon is illuminated with light (photon energy E g ) such that
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Unformatted text preview: carriers are created uniformly everywhere in the sample at the rate of 4 X 10 18 cm-3 s-1 . If the lifetime of the carriers is 10-6 sec, what is the change in conductivity due to the exposure to light. Assume a steady state condition, i.e. carrier concentrations are constant in time. Use mobilities for intrinsic silicon: μ ni = 1420 cm 2 V-1 s-1 , μ pi = 500 cm 2 V-1 s-1 4. Calculate the widths of the space charge region, x n , x p , and x d in an abrupt p-n junction under thermal equilibrium conditions (T=300 K) with N A = 5 X 10 16 cm-3 and N D = 10 16 cm-3 . Take the value of the permittivity of silicon as 11.9 x 8.854 x 10-14 farads/cm....
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