# VLSI Questions and Answers – Doping Process of GA-2

«
»

This set of VLSI Question Bank focuses on “Doping Process of GA-2”.

1. ______ is a direct gap material with valence bond maximum.
a) silicon
b) gallium oxide
c) gallium arsenide
d) silicon arsenide

Explanation: Gallium arsenide is a direct gap material with valence bond maximum and conduction band minimum.

2. Narrow valleys correspond to
a) electrons with lower mass state
b) protons with lower mass state
c) electrons with higher mass state
d) protons with higher mass state

Explanation: Valleys with band structure that are narrow and sharply curved corresponds to electrons with low effective mass state while valleys that are wide are characterized by larger effective masses.

3. 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

Explanation: The curvature of energy versus electron momentum profile determines the effective mass of electrons travelling through the crystal.

4. Conduction band minimum occurs at
a) low momentum
b) high momentum
c) all of the mentioned
d) none of the mentioned

Explanation: 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.

5. Mobility depends on
a) concentration of impurity
b) temperature
c) electron efficient mass
d) all of the mentioned

Explanation: Mobility depends on several factors such as concentration of impurity, temperature and is relatively related to electron efficient mass.

6. 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

Explanation: For GaAs, the effective mass of these electrons is 0.067 times the mass of a free electron.

7. Electrons travels faster in
a) silicon
b) gallium arsenide
c) aluminium
d) silicon oxide

Explanation: 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.

8. Electrons is low valley have high mass.
a) true
b) false

Explanation: Electrons in the higher valleys have high mass and strong intervalleys scattering and therefore exhibit very low mobility.

9. The probability of photon emission has energy which is _______ the band gap.
a) greater than
b) lesser than
c) equal to
d) does not depend on

Explanation: The probability of photon emission with energy nearly equal to the band gap is high, GaAs makes an excellent light-emitting diode.

10. Silicon can also be used as light-emitting device.
a) true
b) false

Explanation: Silicon cannot be used as light-emitting device. It is indirect-gap semiconductor with the conduction gap minimum separated in momentum from valence band minimum.

11. As the applied field increases
a) drift velocity increases
b) energy decreases
c) drift velocity remains constant
d) energy remains constant

Explanation: 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.

12. Saturation velocity is attained when
a) energy gained is greater than energy lost
b) energy lost is greater than energy gained
c) energy gained equals energy lost
d) energy is fully drained

Explanation: 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.

Sanfoundry Global Education & Learning Series – VLSI. 