11. If the equivalent direction is not used ______ will be increased.
A. ion concentration
B. steering angle
C. area coverage
D. depth distribution
Answer: D
If a random equivalent direction is not used during ion implantation, the depth distribution will be greater than those predicted by range statistics which are used to establish penetration depth.
12. Electrons become hot in gallium arsenide when the energy of
A. lower valley electrons decreases
B. lower valley electrons rises
C. higher valley electrons decreases
D. higher valley electrons rises
Answer: B
In gallium arsenide, when the energy of lower valley electrons rises sufficiently at a higher electric field, the electrons become hot.
13. When electrons become hot, drift velocity
A. increases
B. decreases
C. remains the same
D. does not depend on drift velocity
Answer: B
When electrons become hot, there will be a reduction in the number of high mobility electrons and hence a decrease in drift velocity.
14. ______ is a direct gap material with a valence bond maximum.
A. silicon
B. gallium oxide
C. gallium arsenide
D. silicon arsenide
Answer: C
Gallium arsenide is a direct gap material with a valence bond maximum and conduction band minimum.
15. Narrow valleys correspond to
A. electrons with lower mass state
B. protons with lower mass state
C. electrons with a higher mass state
D. protons with higher mass state
Answer: A
Valleys with band structures that are narrow and sharply curved correspond to electrons with a low effective mass state while valleys that are wide are characterized by larger effective masses.
16. The curvature of ___________ determines the effective mass of electrons.
A. energy versus concentration
B. energy versus mass
C. energy versus momentum
D. energy versus structural design
Answer: C
The curvature of the energy versus electron momentum profile determines the effective mass of electrons traveling through the crystal.
17. Conduction band minimum occurs at
A. low momentum
B. high momentum
C. all of the mentioned
D. none of the mentioned
Answer: B
The minimum point of gallium arsenide’s conduction band is near the zero point of the crystal-lattice momentum. Conduction band minimum occurs at high momentum.
18. Mobility depends on
A. concentration of impurity
B. temperature
C. electron efficient mass
D. all of the mentioned
Answer: D
Mobility depends on several factors such as concentration of impurity, and temperature and is relatively related to electron efficient mass.
19. The effective mass of GaAs is _________ than the mass of a free electron.
A. 0.67 times greater
B. 0.67 times lesser
C. 0.067 times greater
D. 0.067 times lesser
Answer: C
For GaAs, the effective mass of these electrons is 0.067 times the mass of a free electron.
20. Electrons travel faster in
A. silicon
B. gallium arsenide
C. aluminum
D. silicon oxide
Answer: B
Electrons travel faster in gallium arsenide than in silicon as the result of their superior electron mobility brought out by the shapes of their conduction bands.
21. Electrons in the low valley that have high mass.
A. true
B. false
Answer: B
Electrons in the higher valleys have high mass and strong intervalley scattering and therefore exhibit very low mobility.
22. The probability of photon emission has an energy which is _______ the bandgap.
A. greater than
B. lesser than
C. equal to
D. does not depend on
Answer: C
The probability of photon emission with energy nearly equal to the bandgap is high, GaAs make an excellent light-emitting diode.
23. Silicon can also be used as a light-emitting device.
A. true
B. false
Answer: B
Silicon cannot be used as a light-emitting device. It is an indirect-gap semiconductor with the conduction gap minimum separated in momentum from the valence band minimum.
24. As the applied field increases
A. drift velocity increases
B. energy decreases
C. drift velocity remains constant
D. energy remains constant
Answer: A
As long as the resultant balance is positive, the energy and drift velocity of the charge carriers increases with an increase in the applied field.
25. Saturation velocity is attained when
A. energy gained is greater than energy lost
B. energy lost is greater than the energy gained
C. energy gained equals energy lost
D. energy is fully drained
Answer: C
The energy gained from the field equals the energy lost as a result of collisions. At this point, drift velocity attains a limiting value called saturation velocity.
26. The GaAs fabrication has _________ gate geometry.
A. less than one micron
B. less than two micron
C. more than one micron
D. more than two micron
Answer: A
The GaAs fabrication has characteristics such as having less than on-micron gate geometry and less than two-micron metal pitch.
27. The GaAs structure has upto _______ metal.
A. two-layer
B. three-layer
C. four-layer
D. one-layer
Answer: C
The GaAs fabrication has the feature of having four-layer metal and a four-inch diameter wafer.
28. Electron mobility of gallium arsenide is _______ that of silicon.
A. greater than
B. lesser than
C. same as
D. does not depend on
Answer: A
Electron mobility of gallium arsenide is six to seven times that of silicon resulting in very fast electron transit times.
29. Saturated drift velocity of gallium is _______ to that of silicon.
A. greater
B. lesser
C. approximately same
D. does not depend on
Answer: C
The saturated drift velocity of gallium and silicon is approximately equal. For GaAs, saturation velocity occurs at a lower threshold field than for silicon.
30. Larger energy bandgap _____ parasitic capacitances.
A. increases
B. decreases
C. maintains constant
D. does not affect
Answer: B
A large energy bandgap offers a bulk semi-insulating substrate and minimizes parasitic capacitances and allows easy electrical isolation.
