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ECE 3150 Homework 2
Due 2/12/2009 by 11:10 AM
1.
(Poisson Equation and diffusion Length)
For a ptype extrinsic Si with the acceptor doping
N
A
=2
10
17
cm
3
, the minority mobility
n
=750cm
2
/Vs, the majority mobility
p
=300cm
2
/Vs, the
minority lifetime
n
=2
10
7
s, and the relative dielectric constant of Si is 11.7,
(a)
Estimate the potential curvature (defined from the Poisson equation) when the majority carriers
are somehow all depleted. (4 pts)
(b)
If we start from a region where the net charge, electric field and electrostatic potential is all zero,
when we enter the majoritycarrier depleted region for 100nm, what are the values of the electric
field and electrostatic potential at the end of the 100nm charged region? (4 pts)
(c)
At equilibrium, calculate the minority diffusion length as defined in Prob. 4(b). Is it smaller or
larger than 1
m? (4 pts)
(d)
Given that the voltage drop in a semiconductor junction is most often smaller than
E
gap
/q
, how do
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This note was uploaded on 03/08/2010 for the course ECE 3150 taught by Professor Spencer during the Spring '07 term at Cornell.
 Spring '07
 SPENCER
 Microelectronics

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