NNSE 618
Home assignment # 2
Due: October 11, 2011
1 An electron concentration in a GaAs sample at room temperature is
10
19
cm
3
.
What
is the position of the Fermi level with respect to the bottom of the conduction band?
(The
effective density of states in the conduction band of GaAs at room temperature is
4.7x10
17
cm
3
.).
Higher?
Lower?
Why? (2 points).
2. The effective densities of states in the conduction and valence bands of GaAs at room
temperature are 4.7x10
17
cm
3
and 7x10
18
cm
3
, respectively.
How many electrons do
you expect to find in a one millimeter cube of undoped GaAs at room temperature?
How
many holes?
The energy gap of GaAs is 1.42 eV. (2 points).
3. What if the same (as in the problem 2) GaAs cube is doped with shallow donors with
concentration 10
13
cm
3
. How many electrons do you expect to find now?
How many
holes?
(3 points).
4. Two degenerate GaAs samples #1 and #2 have electron concentrations
n
1
and
n
2
such
that
n
2
/
n
1
=8.
The Fermi level in sample #1 is 40 meV above the bottom of the
conduction band.
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 Spring '11
 SergeOktyabrsky
 room temperature, conduction band, carrier concentration, GaAs, degenerate GaAs samples

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