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# HW4 - EE2 Problem Set#4 Solutions Due May 03 in class...

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EE2 Problem Set#4 Solutions: Due May 03 in class Question#1 (15 points): A silicon wafer (N A =10 14 /cm 3 , τ n =1 microsec, T=room temperature) is first illuminated for a time t>> τ n with light that generates G LO = 10 16 electron-hole pairs per cm 3 -sec uniformly throughout the volume of the silicon. At time t = 0 the light intensity isredused making G L =G LO /2 for t>0. Determine Δ n p ( t ) for t>0. The initial illumination is present for a time very much longer than the minority-carrier lifetime. Thus, prior to reducing the light intensity, the excess carrier concentration will have reached a steady value Δ n (0) = G L0 τ n = 10 16 × 10 -6 = 10 10 cm -3 (thus, low-level injection prevails). With the illumination reduced, we now need to solve the minority-carrier diffusion equation dΔ n /d t = -(Δ n / τ n ) + ( G L0 /2), where we have noted that the illumination is uniform throughout the sample. Since this equation is subject to the boundary condition D n (0) = G L0 τ n and noting the form of the solution

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HW4 - EE2 Problem Set#4 Solutions Due May 03 in class...

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