Homework 3
1.
Consider an abrupt pn diode  made of an unknown
semiconductor  in thermal equilibrium with as many donors in
the
n
type region as acceptors in the
p
type region and a
maximum electric field of 13 kV/cm and a total depletion layer
width of 1
μ
m. (assume
ε
s
/
ε
0
= 12)
a) What is the applied voltage, V
a
?
b) What is the builtin potential of the diode?
c) What are the donor density in the
n
type region and the
acceptor density in the
p
type region?
d) What is the intrinsic carrier density of the semiconductor if
the temperature is 300 K ?
2.
A silicon pn junction (
N
a
= 10
15
cm
3
,
w
p
= 1
μ
m and
N
d
= 4 x
10
16
cm
3
,
w
n
= 1
μ
m) is biased with
V
a
= 0.5 V. Use
μ
n
= 1000
cm
2
/Vs and
μ
p
= 300 cm
2
/Vs. The minority carrier lifetime is
10
μ
s and the diode area is 100
μ
m by 100
μ
m.
a) Calculate the builtin potential of the diode.
b) Calculate the depletion layer widths,
x
n
and
x
p
, and the
widths of the quasineutral regions.
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 Spring '11
 Prof
 Pn junction, Ptype region, minority carrier lifetime, βDC

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