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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