EE506 Semiconductor Physics
Homework Assignment #6
Prof. Steve Cronin
Due November 22, 2011
Optical Properties:
1.)
a.
At what carrier density does Si with a mobility of 1450cm
2
/V
∙s
and
ε
core
=12
begin to have a plasma frequency?
b.
Using the results in (a.), write an expression for the free carrier contribution to
ε(ω)
.
c.
Plot the real and imaginary components of
ε(ω)
.
d.
Find the plasma frequency for doped silicon with
n
=10
18
electrons/cm
3
, in units
of eV.
2.)
a.
Determine the absorption coefficient due to free carrier absorption at a
temperature of 300K and a free space wavelength of 0.9
µ
m for a partially
compensated GaAs samples with
N
d
=2 x 10
18
/cm
3
and
N
a
=1 x 10
18
/cm
3
for the
donor and acceptor concentrations. Assume a mobility of
µ
=3000cm
2
/V
∙s,
ε
core
=15, and
m
*
=0.065 for GaAs.
b.
Where does the Fermi energy in (a) lie?
c.
For heavily doped GaAs the Fermi energy gets pushed way into the band.
In
order to excite an electron into the conduction band, one must go away from
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 '11
 CRONIN
 Photon, Frequency, conduction band, Semiconductor Physics, Prof. Steve Cronin

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