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ee2_winter08_HW5 - EE 2 Professor Harold Fetterman Homework...

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Unformatted text preview: EE 2 Professor Harold Fetterman Homework # 5 Feb 15, 2008 Due Feb. 22 1. Show that in equilibrium the Fermi Energy in a Semiconductor is constant and not a function of position. Assume the Einstein Relationship holds. 2. Use the continuity equation to derive the excess charge concentration as a function of time, in the case of uniform illumination. 3. If an intrinsic piece of Si is illuminated such that carriers are generated at the rate of 1018 cm'3 5'1 uniformly everywhere in the sample, and if the lifetime of the carriers is 10‘6 3, determine the change in electrical conductivity. (a) Show that the minimum conductivity of a semiconductor sample 4- occurs when no= ni (up/ pup/2 (b) What is the expression for the minimum conductivity 6mm? (0) Calculate (5min for Si at 300 K and compare with the intrinsic conductivity. 5. Two scattering mechanisms are present in a semiconductor at room temperature. The mobility, if the first mechanism alone is present, is 500 chV‘ls-l. The mobility if the second mechanism alone is present is 9OOcm2V'1S‘1. What is the mobility of the carriers in the sample? How would you expect this to change with temperature? ...
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