Test for PCPBT Lab
1.
Can position
mechanically?
a. Yes.
b. No.
2.
Electrons in an infinite quantum well are described with energy levels whose
separation:
a. Increases with increasing energy.
b. Decreases with increasing energy.
c. Stays constant.
3.
Energy levels in a finite well are:
a. Lower compared to infinite well results.
b. Higher compared to infinite well results.
c. The same as infinite well results.
4.
When
are
a.
b.
c.
electrons with energy E encounter a potential step with height U > E they
When
are
a.
b.
c.
electrons with energy E encounter a potential step with height U < E they
5.
and
momentum
be
simultaneously
determined
quantum
All reflected back.
Tunnel through.
None of the above.
All transmitted through.
Some might be reflected.
None of the above.
6.
For the case from problem 5, and for energies larger than U, are there electron
energies for which perfect transmission occurs?
a. yes
b. no
7.
Consider a single barrier structure with barrier height U. If an incoming electron
with energy E<U approaches the potential step then the following statements are
true:
a. The electron will be reflected back 100%.
b. There is a finite probability that the electron will tunnel through, i.e it will
be found on the other side of the potential step.
c. None of the above two statements are true.
8.
For the case when the energy of the electron is E>U, then:
a. Perfect transmission over the barrier occurs as E>U.
b. There are some finite quantum-mechanical reflections that occur at certain
energies
c. There is 50% probability that the electron will be transmitted and 50%
probability that it will be reflected.
9.
For the case when the energy of the electron is E>U, then:
a. There are energies for which perfect transmission occurs.
b. There are no energies for which perfect transmission occurs.
c. None of the above.
10.
Consider a double barrier structure as it occurs in resonant tunneling diode.
Assume that the barriers are symmetric and that the electron energy is smaller
than the barrier height. The following statements are true:
a. There is at least one energy value of the incoming electron for which
perfect transmission occurs.
b. There are no energy values for which perfect transmission occurs.
c. For all of the energy values smaller than the barrier height perfect
transmission occurs.
11.
Consider two symmetric double-barrier structures. Assume in the first case that
the barrier width is small and in the second case that the barrier width is high.
When will the resonant quasi-bound state in the well be sharp?
a. When the barrier width is small.
b. When the barrier width is high.
c. When the well width is large.
12.
Now consider a double-barrier structure with asymmetric barriers. What will be
the nature of the transmission through a quasi-bound state?
a. There will be perfect transmission.
b. There will not be perfect transmission.
13.
Consider a symmetric double barrier structure. If
things will happen:
a. The quasi-bound states will move higher
through these levels will be less sharp.
b. The quasi-bound states will move higher
through these levels will be more sharp.
c. The quasi-bound states will move lower
through these levels will be more sharp.
14.
the well width reduces two
in energy and transmission
in energy and transmission
in energy and transmission
Consider the case of three symmetric barriers. What will happen to the quasibound states when compared to an identical double-barrier structure?
a. The energy levels will split in two, the split being larger for the higher
lying states.
b. The energy levels will split in three, the split being larger for the higher
lying states.
c. The energy levels will not split and will be identical to the double barrier
case.
15.
Consider the same triple barrier structure. If the thickness of the middle barrier
decreases then the following will happen.
a. The split in the energy levels will increase due to larger cross-talk between
the two wells.
b. The split in the energy levels will decrease due to larger cross-talk
between the two wells.
c. The split in the energy levels will stay the same.
16.
Consider the same triple barrier structure. If the thickness of the middle barrier
decreases and the width of the wells increases then the following will happen.
a. The quasi-bound states will shift down and the separation between what
should be degenerate levels will reduce.
b. The quasi-bound levels will shift down and the separation between the
what should be nominally degenerate quasi-bound states will increase
c. The quasi-bound levels will shift up and the separation between what
should be nominally degenerate quasi-bound states will reduce.
17.
Consider the case of 10 identical barriers. Due to the cross-talk between the wells
there will be formation of bands consisting of
a. 9 states
b. 10 states
c. 11 states
18.
If one plots the quasi-bound states energy vs. occurrence and considers larger and
larger number of identical wells then
a. Cosine band-structure starts to build up.
b. Parabolic band-structure starts to build up.
c. None of the above.
19.
The formation of band and gaps occurs because of the:
a. Interaction between the wells.
b. Isolation of the wells.
c. None of the above.
20.
The simple Kronig-Penney model for understanding bandstructure corresponds to
the case of:
d. Infinite potential barriers and wells
e. 40 potential barriers and wells.
f. 100 potential barriers and wells.