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Physics for Electrical Engineers
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Homework #4
Due: Mar. 04
th
, 2010
Assume: i) that n
i
in silicon at room temperature is equal to 10
10
cm
3
and ii) that N
C
= N
V
= 2.5 X10
19
cm
3
.
1.
Consider an abrupt pn junction with N
A
= 5 X 10
16
cm
3
and N
D
= 10
16
cm
3
.
What is the excess minority carrier density at the edge of the space charge region
in the two neutral regions of the pn junction under a forward bias of 0.4 V? Take
the value of the permittivity of silicon as 11.9 x 8.854 x 10
14
farads/cm.
2.
Calculate the a) current due to i) electron injection and ii) hole injection and b)
total current in the pn junction in problem 1 under a forward bias of 0.4 V.
Assume a wide base junction. Take the area of the junction to be 4 X 10
4
cm
2
.
The minority carrier diffusion constants are 10 and 25 cm
2
/sec in the neutral n
and p regions respectively. The minority carrier diffusion lengths are 10
3
and 10
2
cm in the neutral n and p regions respectively.
3.
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This note was uploaded on 01/16/2012 for the course EE 101 taught by Professor Williams during the Spring '07 term at UCLA.
 Spring '07
 Williams

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