1. What is the energy bandgap of silicon at room temperature?
A) 0.67 eV
B) 1.12 eV
C) 1.42 eV
D) 3.4 eV
Answer: B) 1.12 eV
Explanation: Silicon has a bandgap of 1.12 eV at 300K.
2. Which of the following is a direct bandgap semiconductor?
A) Silicon
B) Germanium
C) Gallium Arsenide (GaAs)
D) Silicon Carbide (SiC)
Answer: C) Gallium Arsenide (GaAs)
Explanation: GaAs has a direct bandgap making it suitable for optical devices.
3. The intrinsic carrier concentration of silicon at 300K is approximately:
A) 1.0 × 10^10 cm⁻³
B) 2.4 × 10^13 cm⁻³
C) 1.0 × 10^16 cm⁻³
D) 1.0 × 10^19 cm⁻³
Answer: A) 1.0 × 10^10 cm⁻³
Explanation: ni ≈ 1.0 × 10^10 cm⁻³ at 300K for Si.
4. In an intrinsic semiconductor, the Fermi level is located:
A) At the conduction band edge
B) At the valence band edge
C) Near the middle of the bandgap
D) Above the conduction band
Answer: C) Near the middle of the bandgap
Explanation: For intrinsic Si, EF is near midgap (slightly toward valence band due
to effective mass differences).
,5. Which doping creates n-type silicon?
A) Boron
B) Aluminum
C) Phosphorus
D) Gallium
Answer: C) Phosphorus
Explanation: Phosphorus is a Group V donor dopant providing electrons.
6. The law of mass action for semiconductors states:
A) np = ni
B) np = ni²
C) n + p = 2ni
D) n - p = ND
Answer: B) np = ni²
Explanation: np = ni² holds for both intrinsic and extrinsic semiconductors in
thermal equilibrium.
7. What is the effective density of states in the conduction band (Nc) for Si
at 300K?
A) 1.04 × 10^19 cm⁻³
B) 2.8 × 10^19 cm⁻³
C) 1.5 × 10^10 cm⁻³
D) 6.0 × 10^18 cm⁻³
Answer: B) 2.8 × 10^19 cm⁻³
Explanation: Nc ≈ 2.8 × 10^19 cm⁻³ for Si at 300K.
8. Donor atoms in n-type silicon create energy levels:
A) Near the valence band
B) Near the conduction band
C) At mid-gap
D) Above the conduction band
Answer: B) Near the conduction band
Explanation: Donor levels are shallow states just below the conduction band
edge.
9. The drift velocity of carriers saturates at high electric fields due to:
A) Increased impurity scattering
B) Optical phonon scattering
C) Reduced carrier concentration
D) Bandgap narrowing
Answer: B) Optical phonon scattering
,Explanation: At high fields, carriers gain enough energy to emit optical phonons,
limiting velocity.
10. Which expression correctly gives conductivity σ of a semiconductor?
A) σ = q(nμn + pμp)
B) σ = q(nμn - pμp)
C) σ = qni(μn + μp)
D) σ = q/(nμn + pμp)
Answer: A) σ = q(nμn + pμp)
Explanation: Conductivity includes contributions from both electrons and holes.
11. Einstein's relation connects diffusion coefficient D and mobility μ by:
A) D = μkT/q
B) D = μq/kT
C) D = μ(kT)²/q
D) D = μ/kT
Answer: A) D = μkT/q
Explanation: The Einstein relation D = (kT/q)μ = VT·μ where VT is thermal
voltage.
12. The thermal voltage VT = kT/q at 300K is approximately:
A) 0.026 V
B) 0.6 V
C) 1.12 V
D) 0.052 V
Answer: A) 0.026 V
Explanation: VT = (1.38×10⁻²³ × 300)/(1.6×10⁻¹⁹) ≈ 25.9 mV ≈ 26 mV.
13. A semiconductor with ND >> ni is called:
A) Intrinsic
B) Compensated
C) Extrinsic
D) Degenerate
Answer: C) Extrinsic
Explanation: When doping dominates intrinsic carriers, the semiconductor is
extrinsic.
14. The Hall effect is used to measure:
A) Bandgap energy
B) Carrier concentration and mobility
C) Diffusion length
, D) Recombination lifetime
Answer: B) Carrier concentration and mobility
Explanation: Hall measurements give carrier sign, concentration, and (with
resistivity) mobility.
15. Degenerate semiconductors are those where:
A) Carrier concentration equals ni
B) The Fermi level enters the conduction or valence band
C) The bandgap is zero
D) Mobility is zero
Answer: B) The Fermi level enters the conduction or valence band
Explanation: Heavy doping moves EF into the band, making the semiconductor
degenerate.
16. Auger recombination is most significant in:
A) Lightly doped material
B) Heavily doped material
C) Only at low temperatures
D) Only in direct bandgap materials
Answer: B) Heavily doped material
Explanation: Auger recombination rate ∝ n² (or p²), so it dominates at high carrier
concentrations.
17. Shockley-Read-Hall (SRH) recombination occurs through:
A) Band-to-band transitions
B) Trap states in the bandgap
C) Auger processes
D) Surface states only
Answer: B) Trap states in the bandgap
Explanation: SRH involves deep-level traps near mid-gap as recombination
centers.
18. The minority carrier diffusion length L is given by:
A) L = √(Dτ)
B) L = Dτ
C) L = D/τ
D) L = √(D/τ)
Answer: A) L = √(Dτ)
Explanation: L = √(Dτ) where D is diffusivity and τ is minority carrier lifetime.
19. Continuity equation for holes includes terms for:
A) 0.67 eV
B) 1.12 eV
C) 1.42 eV
D) 3.4 eV
Answer: B) 1.12 eV
Explanation: Silicon has a bandgap of 1.12 eV at 300K.
2. Which of the following is a direct bandgap semiconductor?
A) Silicon
B) Germanium
C) Gallium Arsenide (GaAs)
D) Silicon Carbide (SiC)
Answer: C) Gallium Arsenide (GaAs)
Explanation: GaAs has a direct bandgap making it suitable for optical devices.
3. The intrinsic carrier concentration of silicon at 300K is approximately:
A) 1.0 × 10^10 cm⁻³
B) 2.4 × 10^13 cm⁻³
C) 1.0 × 10^16 cm⁻³
D) 1.0 × 10^19 cm⁻³
Answer: A) 1.0 × 10^10 cm⁻³
Explanation: ni ≈ 1.0 × 10^10 cm⁻³ at 300K for Si.
4. In an intrinsic semiconductor, the Fermi level is located:
A) At the conduction band edge
B) At the valence band edge
C) Near the middle of the bandgap
D) Above the conduction band
Answer: C) Near the middle of the bandgap
Explanation: For intrinsic Si, EF is near midgap (slightly toward valence band due
to effective mass differences).
,5. Which doping creates n-type silicon?
A) Boron
B) Aluminum
C) Phosphorus
D) Gallium
Answer: C) Phosphorus
Explanation: Phosphorus is a Group V donor dopant providing electrons.
6. The law of mass action for semiconductors states:
A) np = ni
B) np = ni²
C) n + p = 2ni
D) n - p = ND
Answer: B) np = ni²
Explanation: np = ni² holds for both intrinsic and extrinsic semiconductors in
thermal equilibrium.
7. What is the effective density of states in the conduction band (Nc) for Si
at 300K?
A) 1.04 × 10^19 cm⁻³
B) 2.8 × 10^19 cm⁻³
C) 1.5 × 10^10 cm⁻³
D) 6.0 × 10^18 cm⁻³
Answer: B) 2.8 × 10^19 cm⁻³
Explanation: Nc ≈ 2.8 × 10^19 cm⁻³ for Si at 300K.
8. Donor atoms in n-type silicon create energy levels:
A) Near the valence band
B) Near the conduction band
C) At mid-gap
D) Above the conduction band
Answer: B) Near the conduction band
Explanation: Donor levels are shallow states just below the conduction band
edge.
9. The drift velocity of carriers saturates at high electric fields due to:
A) Increased impurity scattering
B) Optical phonon scattering
C) Reduced carrier concentration
D) Bandgap narrowing
Answer: B) Optical phonon scattering
,Explanation: At high fields, carriers gain enough energy to emit optical phonons,
limiting velocity.
10. Which expression correctly gives conductivity σ of a semiconductor?
A) σ = q(nμn + pμp)
B) σ = q(nμn - pμp)
C) σ = qni(μn + μp)
D) σ = q/(nμn + pμp)
Answer: A) σ = q(nμn + pμp)
Explanation: Conductivity includes contributions from both electrons and holes.
11. Einstein's relation connects diffusion coefficient D and mobility μ by:
A) D = μkT/q
B) D = μq/kT
C) D = μ(kT)²/q
D) D = μ/kT
Answer: A) D = μkT/q
Explanation: The Einstein relation D = (kT/q)μ = VT·μ where VT is thermal
voltage.
12. The thermal voltage VT = kT/q at 300K is approximately:
A) 0.026 V
B) 0.6 V
C) 1.12 V
D) 0.052 V
Answer: A) 0.026 V
Explanation: VT = (1.38×10⁻²³ × 300)/(1.6×10⁻¹⁹) ≈ 25.9 mV ≈ 26 mV.
13. A semiconductor with ND >> ni is called:
A) Intrinsic
B) Compensated
C) Extrinsic
D) Degenerate
Answer: C) Extrinsic
Explanation: When doping dominates intrinsic carriers, the semiconductor is
extrinsic.
14. The Hall effect is used to measure:
A) Bandgap energy
B) Carrier concentration and mobility
C) Diffusion length
, D) Recombination lifetime
Answer: B) Carrier concentration and mobility
Explanation: Hall measurements give carrier sign, concentration, and (with
resistivity) mobility.
15. Degenerate semiconductors are those where:
A) Carrier concentration equals ni
B) The Fermi level enters the conduction or valence band
C) The bandgap is zero
D) Mobility is zero
Answer: B) The Fermi level enters the conduction or valence band
Explanation: Heavy doping moves EF into the band, making the semiconductor
degenerate.
16. Auger recombination is most significant in:
A) Lightly doped material
B) Heavily doped material
C) Only at low temperatures
D) Only in direct bandgap materials
Answer: B) Heavily doped material
Explanation: Auger recombination rate ∝ n² (or p²), so it dominates at high carrier
concentrations.
17. Shockley-Read-Hall (SRH) recombination occurs through:
A) Band-to-band transitions
B) Trap states in the bandgap
C) Auger processes
D) Surface states only
Answer: B) Trap states in the bandgap
Explanation: SRH involves deep-level traps near mid-gap as recombination
centers.
18. The minority carrier diffusion length L is given by:
A) L = √(Dτ)
B) L = Dτ
C) L = D/τ
D) L = √(D/τ)
Answer: A) L = √(Dτ)
Explanation: L = √(Dτ) where D is diffusivity and τ is minority carrier lifetime.
19. Continuity equation for holes includes terms for:
