ECE 440
Homework VII
Fall 2009
Due: Friday, Oct 23, 2009
1.
Fieldeffect transistors control the output current by changing the charge density in
the active region. The following problem is designed to illustrate the effect of
changing charge density on the output current. Assume that a rectangular bar of
silicon shown below consists of two layers, each of thickness t
1
and t
2
, respectively.
The dimensions are D=100μm, W=4μm, t
2
=5μm and t
1
=100Å. The t
1
layer is
uniformly doped with N
d1
/cm
3
donors and N
d2
=10
14
/cm
3
donors are also uniformly
doped in the t
2
layer. A bias of 1 V is applied between x=0 and x=W. Determine the
output current, I
d
, for different carrier densities in the t
1
layer. Specify the current for
N
d1
=10
17
/cm
3
, 1.1x10
17
/cm
3
, 10
18
/cm
3
, and 1.01x10
18
/cm
3
. Also, estimate the
“Amplification Factor” of this device for N
d1
=10
17
/cm
3
and N
d1
=10
18
/cm
3
. The
“Amplification Factor” is defined as AF= (1/qt
1
)(
∆
I
d
/
∆
N
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 Spring '08
 Staff
 Transistor, Bipolar junction transistor, Pn junction

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