homework 5 solutions

# homework 5 solutions - ― despite perhaps lowered mobility...

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1 Homework #5, Due 10/30/07 I. (25 points) Problem 5.9 of text. Assume complete ionization. (a) eV 407 . 0 cm / 10 5 . 1 cm / 10 ln eV 0259 . 0 ln 3 10 3 17 , , = × = = i p o B F p i n p T k E E eV 347 . 0 cm / 10 5 . 1 cm / 10 ln eV 0259 . 0 ln 3 10 3 16 , , = × = = i n o B n i F n n T k E E 0.754eV eV 347 . 0 eV 407 . 0 ) ( ) ( , , = + = + = n i F F p i o E E E E qV eV 754 . 0 ) cm / 10 5 . 1 ( ) cm / 10 )( cm / 10 ( ln eV 0259 . 0 ln ln 2 3 10 3 16 3 17 2 2 , , = × = = i d a B i n o p o B o n N N T k n n p T k qV II. (25 points) Problem 5.21 of text. (a) increases (W decreases, so capacitance increases) (b) increases (Fermi level closer to conduction band on n-side so contact potential is larger, as per problem 5.9 above) (c) decreases (W decreases, so peak field magnitude must increase to produce the same electrostatic potential drop across the depletion region. Or the potential drop and thus the reverse bias voltage can be less to produce the same fields, allowing either Zener tunneling or avalanche breakdown whichever comes first to occur at lower reverse biases). (d) decreases (More doping leads to more conductivity

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