UNIT – 04 – SEMICONDUCTOR PHYSICS
Easy
1. An intrinsic semiconductor is:
a) A semiconductor that is doped with impurities
b) A semiconductor made of pure material
c) A conductor at high temperatures
d) A material with a wide band gap
Answer: b) A semiconductor made of pure material
2. In a semiconductor, the conduction band is:
a) Completely full of electrons
b) Empty
c) Partially filled with electrons
d) Same as the valence band
Answer: c) Partially filled with electrons
3. In intrinsic semiconductors, the concentration of electrons in the
conduction band is:
a) Equal to the concentration of holes in the valence band
b) Very high
c) Zero
d) Only a small fraction of the total number of atoms
Answer: a) Equal to the concentration of holes in the valence band
4. A semiconductor with a direct band gap:
a) Does not emit light when electrons fall to the valence band
b) Requires phonons for electron transitions
c) Can emit light directly by electron transition
d) Has a very low conductivity
Answer: c) Can emit light directly by electron transition
5. The energy band diagram of a semiconductor shows:
a) The atomic structure of the material
b) The potential energy levels of electrons in the material
c) The number of free electrons in the material
d) The color of the semiconductor
Answer: b) The potential energy levels of electrons in the material
6. A direct band gap semiconductor:
a) Requires the involvement of phonons for transitions
b) Has its conduction band minimum and valence band maximum at different
points in the k-space
c) Allows electron transitions without the involvement of phonons
d) Has a higher resistivity than an indirect band gap semiconductor
Answer: c) Allows electron transitions without the involvement of phonons
7. The intrinsic carrier concentration in an intrinsic semiconductor depends
on:
a) The material's atomic number
b) The temperature
c) The applied voltage
d) The thickness of the semiconductor
Answer: b) The temperature
8. In an intrinsic semiconductor, the number of free electrons in the
conduction band is equal to:
a) The number of holes in the conduction band
b) The number of atoms in the semiconductor
c) The number of holes in the valence band
d) Zero
Answer: c) The number of holes in the valence band
9. Band gap determination is important because:
a) It tells how fast electrons move in a semiconductor
b) It helps to determine the material’s electrical conductivity and optical
properties
c) It controls the temperature of the material
d) It gives information about the color of the material
Answer: b) It helps to determine the material’s electrical conductivity and
optical properties
10. Extrinsic semiconductors are created by:
a) Changing the atomic structure of intrinsic semiconductors
b) Doping intrinsic semiconductors with impurities
c) Changing the temperature of the semiconductor
d) Applying a voltage to the semiconductor
Answer: b) Doping intrinsic semiconductors with impurities
Moderate
11. The Hall effect in semiconductors is used to measure:
a) The energy gap of a material
b) The type of semiconductor (n-type or p-type)
c) The magnetic field strength
d) The concentration of charge carriers
Answer: d) The concentration of charge carriers
12. The Hall coefficient is a measure of:
a) The energy band gap
b) The carrier concentration and type (n-type or p-type)
c) The electrical conductivity
d) The refractive index of a semiconductor
Answer: b) The carrier concentration and type (n-type or p-type)
13. In a PN junction, the region between the p-type and n-type
semiconductors is known as the:
a) Conduction band
b) Valence band
c) Depletion region
d) Energy gap
Answer: c) Depletion region
14. In forward bias, the PN junction:
a) Expands the depletion region
b) Allows current to flow easily
c) Prevents current flow
d) Has no effect on the current flow
Answer: b) Allows current to flow easily
15. In reverse bias, the PN junction:
a) Reduces the width of the depletion region
b) Causes a large current to flow
c) Prevents current from flowing easily
d) Increases the number of charge carriers in the region
Answer: c) Prevents current from flowing easily
16. The Schottky diode is formed by:
a) Joining a p-type semiconductor with a metal
b) Joining an n-type semiconductor with a metal
c) Joining a p-type semiconductor with an n-type semiconductor
d) Using a high-energy photon to create a junction
Answer: b) Joining an n-type semiconductor with a metal
17. Tunnel diodes are characterized by:
a) A large forward bias
b) Quantum tunneling and a very thin depletion region
c) A long charge relaxation time
d) A high resistance
Answer: b) Quantum tunneling and a very thin depletion region
18. The formation of a PN junction involves:
a) Placing two metals together
b) Doping different parts of a semiconductor with p-type and n-type impurities
c) Cooling the semiconductor
d) Applying a large voltage to the material
Answer: b) Doping different parts of a semiconductor with p-type and n-type
impurities
19. Carrier concentration in an intrinsic semiconductor is:
a) Zero
b) Dependent on the temperature
c) Dependent on the applied voltage
d) Higher than in an extrinsic semiconductor
Answer: b) Dependent on the temperature
20. In a direct band gap semiconductor, an electron transition from the
conduction band to the valence band:
a) Can only happen with the assistance of a phonon
b) Emits light directly
c) Requires high energy to occur
d) Does not occur under normal conditions
Answer: b) Emits light directly
Hard
21. In an indirect band gap semiconductor, an electron transition from the
conduction band to the valence band:
a) Happens without the involvement of phonons
b) Requires the assistance of a phonon to conserve momentum
c) Happens at a very low temperature
d) Occurs only at high electric fields
Answer: b) Requires the assistance of a phonon to conserve momentum
22. The majority carriers in a p-type semiconductor are:
a) Electrons
b) Holes
c) Photons
d) Ions
Answer: b) Holes
23. The majority carriers in an n-type semiconductor are:
a) Electrons
b) Holes
c) Protons
d) Neutrons
Answer: a) Electrons
24. The conductivity of a semiconductor is given by:
a) The product of the charge of the electron and the electric field
b) The product of the charge carrier concentration, charge, and mobility
c) The inverse of the resistance
d) The voltage divided by the current
Answer: b) The product of the charge carrier concentration, charge, and
mobility
25. In a reverse biased PN junction, the width of the depletion region:
a) Decreases
b) Increases
c) Remains constant
d) Becomes zero
Answer: b) Increases
26. In a Schottky diode, the metal-semiconductor junction behaves as:
a) A high resistance at both forward and reverse bias
b) A rectifying junction with a low forward voltage drop
c) An ideal conductor
d) A non-conductive junction
Answer: b) A rectifying junction with a low forward voltage drop
27. In a tunnel diode, the phenomenon of quantum tunneling allows:
a) A large current to flow even under small reverse bias
b) A high resistance under forward bias
c) A small current to flow only under high bias conditions
d) A decrease in the effective charge carrier mobility
Answer: a) A large current to flow even under small reverse bias
28. The Hall coefficient for an n-type semiconductor is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: b) Negative
29. The intrinsic carrier concentration in a semiconductor increases with:
a) Increasing temperature
b) Decreasing temperature
c) Applying a reverse bias
d) Applying a forward bias
Answer: a) Increasing temperature
30. The Schottky barrier height depends on:
a) The electron affinity of the semiconductor
b) The doping concentration of the semiconductor
c) Both a and b
d) The temperature of the semiconductor
Answer: c) Both a and b
