ece340Fall03HW4sol

# ece340Fall03HW4sol - ECE 340 Homework IV Fall 2003 Due...

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ECE 340 Homework IV Fall 2003 Due: Monday, September 22, 2003 1. A compensated germanium sample is doped with 1x10 17 /cm 3 acceptors and 5x10 13 /cm 3 donors. (a) What is the electron and hole concentration respectively at room temperature under equilibrium conditions? Repeat for (b) 1x10 15 /cm 3 acceptors and 5x10 13 /cm 3 donors (c) 1x10 14 /cm 3 acceptors and 5x10 13 /cm 3 donors and (d) 5.1x10 13 /cm 3 acceptors and 5x10 13 /cm 3 donors. Determine the percentage of error in each case for the majority carrier concentration if one simply assumes that the majority carrier concentration approximately equals the difference between the densities of donors and acceptors. Solutions: From Fig 3-17, 13 3 (300 ) 2.5 10 i nK c m . Use charge neutrality equation: da Np Nn +− + =+ , 13 3 51 0 d Nc m + Since at thermal equilibrium, 2 i n n p = , We have: () 22 0 ad i nN N n n −+ −− = , solving this quadratic equation gives: 2 2 4 2 i NN n p −± + = , N a (cm –3 ) 17 11 0 × 15 0 × 14 0 × 13 5.1 10 × n (cm –3 ) 16 9.995 10 × 14 9.507 10 × 13 6.036 10 × 13 2.551 10 × Assume ' p =− (cm –3 ) 16 9.995 10 × 14 9.5 10 × 13 0 × 12 0

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ece340Fall03HW4sol - ECE 340 Homework IV Fall 2003 Due...

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