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Unformatted text preview: Problem I (25 points) Consider a silicon pn junction with a cross—sectional area of 10'4 cm2 and the
following parameters at T = 300K:
N =1017cm_3,N =5x1015cm‘3,r =10_7s,r 210—63
d a p 72
pp 2 400 cm: / V.S, it" = 1000 cm; / VS a) (10 points) Sketch the thermalequilibrium energyband diagram across the pn
junction. 1 b) (5 points) Determine the ratio of the hole current to total current at the space
charge edge xn c) (5 points) Determine the ratio of the electron current to total current at the space
charge edge —xp d) (5 points) Calculate the total number of excess electrons in the p region for
Va=0.5V P
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T D? Air 99“.““(3 1 Ln DP i>In0 Problem 2 (25 points) Consider an Si pnp transistor with NE= 21‘11017 cm'3, N3 = 2x1016 cm'3, NC = 2xlO15
cm'3. The metallurgical base width is 1 um and the base cross sectional area is 10
mm. Assume the critical ﬁeld to be equal to 105 V/cm. a? ni =1.5x1010 0114,83 =11.7x 8.854x10‘14F/cm a) (5 points) Draw the energy band diagram under equilibrium. b) (5 points) Sketch the electric ﬁeld, charge density, and determine the potential
between the emitter and collector. c) (5 points) For VEB = 0.7V, VEC : 2.0V, draw the excess minority carrier
densities across the emitter, base, and collector regions. (1) (5 points) Determine the total number of excess holes in the undepleted part of the base.
e) (5 points) Determine the commonbase breakdown voltage. (AM Problem 3 (25 points) A MOSFET has the following parameters: 0 l
p+ poly gate, r =100A,N =1016cm‘3,QSS =1011cm‘2 0x A
n: =1.5x1l)‘0 01114, 60 = 3.9x8.854x10‘14 F/cm as =11.7x78.854x10‘14 F/cm QSS is the number of electronic charges per unit area in the oxide a) (10 points) Determine the threshold voltage.
b) (5 points) Is the device enhancement or depletion type? Explain.
c) (10 points) What type of implant and dose are required such that VT = 1V hi “L
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1 5 2 cm_3,Q =1011cm“ o
11* polysilicon gate, t =500A,N 22x10
a SS 0x W = Sym,L =1,um,,un :IOOOEHLﬁM =3.9£ﬂ, 
.s 80 = 8.854x10'l4F/cm QSS is the number of electronic charges per unit area in the oxide a) (10 points) Determine the threshold voltage.
b) (5 points) Is the transistor enhancement or depletion mode? Explain. c) (10 points) Assume the transistor is biased in the saturation region, plot @ _ versus VGs for VSB=0 and Vsn=3 V. KT L“ (’71
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 Spring '08
 Kamoua,R

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