20101ee115A_1_ee115a_winter10Hw1

20101ee115A_1_ee115a_winter10Hw1 - EE115A Winter10...

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EE115A Frank Chang Winter10 Homework #1 Due Mon, Jan 18th, 2010 noon Problem 1. The intrinsic carrier concentration of germanium (GE) is expressed as 15 3/ 2 3 1.38 10 exp , 2 g i E n T cm kT = × where E g = 0.66eV. (a) Calculate n i at 290K. (b) Assuming 2 3900 /( . ) n cm V s µ = , 2 1900 /( . ) p cm V s µ = and a piece of germanium with length of 0.1 μm and a cross section area of 0.1 μm by 0.1 μm sustains a voltage difference of 1V what is the total current at 290K if it is doped with P at a density of 10 17 cm -3 . Problem 2. Due to a manufacturing error, the p-side of a pn junction has not been doped. If 3 16 10 5 × = cm N D , calculate the built-in potential at T=300K. Problem 3. Two identical pn junctions are placed in series. (a) Prove that this combination can be viewed as a single two-terminal device having an exponential characteristic. (b) For a tenfold change in the current, how much voltage change does such a device require? Problem 4. Figure 1.
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