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To Electron or Not To Electron
To Electron or Not To Electron
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Answers
1
Calculate the concentration of holes in an extrinsic semiconductor
1.39x10^17 cm^-3
3.37x10^16 cm^-3
4.46x10^16 cm^-3
1.39x10^15 cm^-2
2
What is a band gap?
The energy level that houses the material electrons
The energy state that allows for metals to be conductive
An energy zone that does not posses any energy levels.
It is a zone where bands play music
3
The width of an energy band is ~5 eV. Calculate the density of states at the center of the band.
2.93 x 1045
194.9 x 1045
67.08 x 1045
38.46 x 1045
4
What is the difference between an insulator’s and a semiconductor’s band gap?
The insulator’s band gap is shorter
What’s a band gap?
The insulator’s band gap is larger
The band gaps are the same between the two
5
The Seeback Coeffcient that is positive means that the electrons have gathered on the cold side.
False
True
6
What is a phonon?
A small iPhone
A small packet of vibrational energy
A small interstitial defect within the lattice
A small packet of light energy
7
When a molecule has a center of symmetry, the electron wave functions must be _______.
The moon's gravity
antisymmetric
symmetric or antisymmetric
symmetric
8
All electrons in a metal contribute to electrical conduction.
True
False
9
a thermocouple made of Cu and Ni pairing. If one junction is at 0˚C and the other is at 100˚C what is the emf generated?
9.291 mV
9.106 mV
9.329 mV
9.425 mV
10
A trapping center permanently holds onto an electron or hole in a semiconductor.
False
True
11
The mass of an electron in a crystal lattice is equivalent to an electron in a vacuum.
False
True
12
The Schottky Effect bends the work function due to applied field, helping electrons escape.
True
False
13
What wavelengths of light can be absorbed by a Si photodetector given Eg = 3.2 eV?
12.46 um
0.387 um
0.793 um
1.1 um
14
What is an intrinsic semiconductor?
A semiconductor that has no dopants/impurities
A semiconductor made out of one element
A semiconductor made out of two elements
A semiconductor that has dopants/impurities
15
What is left behind in the valence band when an electron jumps to the conduction band?
A Photon
A Positron
A Hole
A Phonon
16
An electron cannot jump a semiconductor’s band gap
True
False
17
Where does the temperature dependence of drift mobility come from?
Ionized Impurities and Electric Field
Lattice Vibrations and Ionized Impurities
Electric Field and Photon Excitation
Photon Excitation and Lattice Vibrations
18
The work function is the energy required to excite an electron from the Fermi level to the vacuum.
True
False
19
What is a piezoresistor?
A semiconductor that changes its resistivity while heated
A metal conductor that changes its resistivity while heated
A metal conductor that changes its resistivity under stress
A semiconductor that changes its resistivity under stress
20
What is required in an indirect semiconductor for recombination that is not required in a direct semiconductor?
An applied electric field
A recombination wave function
A recombination center
A recombination band gap
21
At HIGH temperatures, Lattice Vibrations are the primary factor for drift mobility in a semiconductor.
False
True
22
What causes piezoresistivity to occur in semiconductors?
The strain changes the effective mass that changes mobility
Strain increases the distance between impurities, decreases drift velocity
Stress increases the length, decreasing drift velocity
Stress increases the concentration of defects, restricting drift mobility
23
Calculate the probability of finding an electron at the donor energy level when Ed = Ef + 0.51 eV. Use Fermi-Dirac.
12.3x10^-9
2.72x10^-9
3.56x10^-9
1.95x10^-9
24
What happens with a direct semiconductor that has a long minority carrier lifetime?
The semiconductor slowly loses luminescence
The semiconductor quickly loses luminescence
The semiconductor quickly cools down
The semiconductor slowly cools down
25
What is the combined wave equation for the image below?
A + B + C
A - B + C
A - C
Bro, why are you doing this to us?
26
A molecule has a center of symmetry at B. Which diagrams below show the antisymmetric wavefunction?
A
D
B
C
27
Calculate hole concentration in an n-type when Nd = 3.4x10^20 m^-3 and ni = 1.5x10^16 m^-3. Assume 100% ionization.
2.3x10^4 m^-3
7.7x10^24 m^-3
6.6x10^11 m^-3
4.4x10^-5 m^-3
28
Detrapping an electron requires a(n) ________ for the electron to begin conducting again.
Electric Field
Lattice Vibration
Tunneling
Photon
29
How would the average momentum change when an external field is applied in the positive x direction
Pavg will shift in the negative x
Pavg will shift in the positive x
why are the electrons pink
Pavg will not change
30
If the potential energy barrier for an electron escaping to a vacuum gets thin, the electron can tunnel the barrier.
True
False
31
The flow of electrons in a Schottky Diode will be opposite than the current produced by the device.
False
True
32
Which atom acts as a donor atom in a semiconductor?
Carbon
Phosphorus
Boron
Gallium
33
At an energy close to Eg, a direct semiconductor is more efficient at exciting electrons with photon’s adsorbed energy.
True
False
34
In which theory has all electrons contributing to conduction.
Classical Drude Model
Quantum Theory
35
Are you excited for the exam tomorrow?
No
Eww
Why are electrons bipolar
Yes
36
Optical absorption only occurs when the photon has an energy greater than the bandgap.
False
True
37
What is a degenerate semiconductor?
A semiconductor that has a narrowed band gap
A semiconductor that degrades over time
A semiconductor that behaves more like a metal
A semiconductor that behaves more like an insulator
38
What relationship leads to a Schottky junction?
ɸ_m=ɸ_n
Just no
ɸ_m<ɸ_n
ɸ_m>ɸ_n
39
What is an extrinsic semiconductor?
A semiconductor that has no dopants/impurities
A semiconductor made out of two elements
A semiconductor made out of one element
A semiconductor that has dopants/impurities
40
The contact potential is the energy difference to free an electron from both materials
True
False
41
We can use silicon semiconductors for high efficiency LED.
False
True
42
In extrinsic semiconductors, the equation np=ni^2 doesnt apply because the electron and hole concentrations are unequal.
False
True
43
What can excite electrons across the band gap?
Kinetic Energy
Light
Brownian Motion
Heat
44
What is produced in a direct semiconductor when an electron recombines with a hole?
Kinetic Energy
An Electric Field
A photon
A phonon
45
In an n-type semiconductor, which carrier has the higher concentration?
Cations
Anions
Holes
Electrons
46
Looking only at electron energies, why can't a He-He bond form?
The bond energy is close to zero
The bonding energy is greater than the two isolated He atoms.
The helium atoms didn't get over the cheating scandal.
The isolated He atoms is greater than the bonded energy
