Moreno Valley College
EE MISC
Homework Five (Due: Nov. 21) 1. A Si pn junction has NA = 1e15 / cm3 , ND = 1e17 / cm3 . T=300K and ni = 1e10 / cm3 . (2pt x 9, 3pt for (i)) a. Calculate the built in voltage, Vbi. b. On the plot below, using a straightedge, draw the charge density in the junction using the depletion approximation. c. Calculate the maximum magnitude of the elec
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Homework Five (Due: Nov. 21) 1. A Si pn junction has NA = 1e15 / cm3 , ND = 1e17 / cm3 . T=300K and ni = 1e10 / cm3 . (2pt x 9, 3pt for (i)) a. Calculate the built in voltage, Vbi. b. On the plot below, using a straightedge, draw the charge density in the junction using the depletion approximation. c. Calculate the maximum magnitude of the electric field in the junction in terms of both xp and xn corresponding to the charge density. d. Using a straightedge, draw the electric field in the junction on the plot below. e. From the electric field, calculate the maximum value of the voltage in terms of xn and xp. f. Calculate the depletion width, W. g. Calculate the depletion width on the n-side, xn. h. Calculate the depletion width on the p-side, xp. i. Determine the voltage at x=0. j. Calculate the capacitance, Cj. (a) Vbi = kT q ln NAND ni 2 æ è ç ö ø ÷ = 0.026 ´ ln 10 32 10 20 æ è ç ö ø ÷ = 0.7184 V (c) (e) (f) Its fine to just use the equation for W below, since we derived it in class. NA xp = ND xn Þ xn = NA ND xp W = (xp + xn ) = xp 1+ NA ND æ è ç ö ø ÷ Þ xp = W ND NA + ND æ è ç ö ø

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