Compare the Hall constant found in the problem 8-2 above with that
found for copper in Homework set 7. Answer the following questions with
brief explanations:
a. In the semiconductor in problem 8-2, how would you expect
the Hall coefficient vary as temperature approaches 0?
b. In copper, how would you expect
the Hall coefficient vary as temperature approaches 0?
c. In the semiconductor in problem 8-2, how would you expect
the Hall coefficient change if there were 1013 acceptors/cm3
and no donors?
State in your own words the reason that a p-n junction is a rectifier.
Which direction of current is passed and which is blocked by the
rectifying action? Define current in the conventional sense of the
direction of flow of positive charge per unit time, and state the direction in terms of "n to p"
or "p to n".
Sketch schematically the variations of the bands in space for
a n-p-n transistor. On the same diagram show schematically
the density of electrons and holes.
A quantum well 20 nm thick is made of GaAs, with AlAs on either
side. Assume that the energy of an electron in AlAs is much higher than
in GaAs, so that the electrons are confined to the GaAs layer.
(They are still free to move in two dimensions.)
Find the lowest energy possible for an electron in this well
relative to the energy of an electron at the bottom of the conduction
band in a large crystal of GaAs. (Use the effective mass given in Kittel.)
Describe briefly why electrons in the quantum well in the previous problem
can be considered to be a "two-dimensional electron gas" even though in fact
it had a thickness in the third dimension.
A quantum dot confines the electrons in all dimensions. What is
are the lowest two allowed energies for an electron in a cubic
box of GaAs 20 nm on each side?