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Unformatted text preview: Homework 5 1. Problem: A silicon pn junction is formed between ntype Si doped with N D = 10 17 cm 3 and ptype Si doped with N A = 10 16 cm 3 . (a) Sketch the energy band diagram. Label all axes and all important energy levels. (b) Find n n , n p , p p , and p n . Sketch the carrier concentration (of both electrons and holes) as a function of position. (c) Calculate the builtin potential V bi in eV. Solution: (a) The energy band diagram with labeled important energy levels and axes is (b) Given n i = 1 . 5 10 10 cm 3 , in the quasineutral pregion, ECE344 Fall 2009 1 p p = N A = 10 16 cm 3 . (1) In the quasineutral nregion, n n = N D = 10 17 cm 3 . (2) In the depletion region, n p = n 2 i N A = 2 . 25 10 4 cm 3 (3) for pside and p n = n 2 i N D = 2 . 25 10 3 cm 3 (4) for nside. The diagram for carrier concentration is: ECE344 Fall 2009 2 (c) Using Eq. (123) or (124) on lecture notes Part 2, the buildin potential is V bi = k B T q ln ( N A N D n 2 i ) = k B T q ln ( p p p n ) = 0 . 7543 eV. (5) 2. Problem: A Si pn junction has dopant concentrations N D = 2 10 15 cm 3 and N A = 2 10 16 cm 3 . Calculate the builtin potential V bi in eV and the total width of the depletion region W = x n + x p at zero bias (that is, V a = 0 ) and under a reverse bias V a = 8 V....
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This note was uploaded on 09/13/2010 for the course ECE ECE344 taught by Professor Polizinni during the Spring '10 term at University of Massachusetts Boston.
 Spring '10
 Polizinni

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