Homework 4
A silicon pn diode maintained at 300K has a doping of N
a
=3x10
18
cm
3
and N
d
=1.0x10
16
cm
3
and mobilities in the two regions of
µ
n
=1000 cm
2
/VSec,
µ
p
=200 cm
2
/VSec,
minority carrier lifetimes in the two regions of
τ
n
=10
µ
S
τ
p
=1.2
µ
S.
1)
What is the built in voltage?
2)
What is the depletion width (total, W) and width on each side of the junction (x
n
and x
p
3)
Why is the value of x
)?
p
different from x
n
4)
What is the leakage current density, Jo (not Io)?
(i.e. why is the depletion region
asymmetric)?
5)
Write out the JV equation of the diode explaining which part is due to diffusion
current and which part is due to drift current.
6)
What is the capacitance per unit area and the small signal diode resistance at 0
volts? (Assuming the diode area is 2.0e5 cm
2
7)
What is the capacitance per unit area and the small signal diode resistance at 3
volts (i.e. reverse bias)?
when solving problems 68)
8)
What is the capacitance per unit area and the small signal diode resistance at +0.5
volts (i.e. forward bias)?
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 Spring '07
 HAMBLEN
 voltage regulator, small signal diode, ideal diode model, signal diode resistance

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