ECE 315 Homework 3
Due 12noon, Sept. 13, 2007 in the drop box
1.
(PN junction, continued from Prob. 7 of HW 2.
Please follow the numbers there. )
For
a pn junction well described by the depletion region approximation as shown below, assume
the electron mobility
μ
n
=1000cm
2
/Vs, the hole mobility
μ
p
=400cm
2
/Vs, and the minority
lifetime
τ
n
=
τ
p
=10
7
s
(a)
In equilibrium, which region(s) satisfy the charge neutrality condition? Explain briefly.
(4 pts)
(b)
In equilibrium, which region(s) satisfy the relation of
np=n
i
2
? Explain briefly. (4 pts)
(c)
At
V
D
=0, Calculate the depletion capacitance in F/cm
2
. (4 pts)
(d)
Estimate the ideal saturation current
I
S
at 250K, 300K and 400K.
You can use the
n
i
values from Problem 2 of Homework 2. Assume
A
= 1cm
2
. (6 pts)
2.
(Generation and recombination in the depletion region)
For the pn junction in Prob. 1,
the voltage across the diode is
V
D
and the current is
I
D
.
(a)
At
V
D
= 0.6V forward bias, what is the minority carrier concentrations at
–x
p
and
x
n
? (4
pts)
(b)
At
V
D
=
–
1.0V reverse bias, what is the minority carrier concentrations at
–x
p
and
x
n
? (4
pts)
(c)
Plot the log(
n
) and log(
p
) throughout the entire device under
V
D
=0V,
V
D
=0.6V and
V
D
=
–
1.0V in the same plot (for better comparison). (4 pts)
(d)
Plot
J
n
,
J
p
and
J
n
+J
p
throughout the entire device under
V
D
=0V,
V
D
=0.6V and
V
D
=
–
1.0V in separate plots. (4 pts)
(e)
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 Fall '07
 SPENCER
 Microelectronics, pts, Bipolar junction transistor, Vbi

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