Semiconductor Fundamentals MCQs

Practice Semiconductor Fundamentals MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Electronic Devices & CircuitsSemiconductor Fundamentals

In an intrinsic semiconductor at thermal equilibrium, the electron concentration n and hole concentration p are related by?

An > p
Bn < p
Cn = p = ni
Dn + p = 0

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Correct Answer: C. n = p = ni

Explanation: In an intrinsic semiconductor, thermally generated electrons and holes occur in equal numbers, so n = p = ni.

Reference: Standard semiconductor electronics: intrinsic carrier concentration

Question 2

Electronic Devices & CircuitsSemiconductor Fundamentals

Doping pure silicon with a pentavalent impurity such as phosphorus generally produces?

AP-type semiconductor
BN-type semiconductor
CIntrinsic semiconductor
DInsulating material

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Correct Answer: B. N-type semiconductor

Explanation: Pentavalent donor atoms contribute extra electrons, making electrons the majority carriers in an n-type semiconductor.

Reference: Standard semiconductor electronics: doping

Question 3

Electronic Devices & CircuitsSemiconductor Fundamentals

In a p-type semiconductor, the majority charge carriers are?

AElectrons
BHoles
CNeutrons
DPositive ions moving through the lattice

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Correct Answer: B. Holes

Explanation: Trivalent acceptor doping creates holes as the majority mobile carriers in p-type material.

Reference: Standard semiconductor electronics: p-type material

Question 4

Electronic Devices & CircuitsSemiconductor Fundamentals

For a nondegenerate semiconductor in thermal equilibrium, the mass-action law is expressed as?

Anp = ni^2
Bn + p = ni^2
Cn/p = ni
Dnp = ni

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Correct Answer: A. np = ni^2

Explanation: At thermal equilibrium, the product of electron and hole concentrations equals the square of the intrinsic carrier concentration: np = ni².

Reference: Standard semiconductor electronics: mass-action law

Question 5

Electronic Devices & CircuitsSemiconductor Fundamentals

If the electron concentration in an n-type semiconductor is 10^16 cm^-3 and ni = 10^10 cm^-3, the equilibrium hole concentration is approximately?

A10^2 cm^-3
B10^4 cm^-3
C10^6 cm^-3
D10^10 cm^-3

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Correct Answer: B. 10^4 cm^-3

Explanation: Using np=ni², p=(10^10)²/10^16=10^4 cm^-3.

Reference: Standard semiconductor electronics: minority carrier concentration

Question 6

Electronic Devices & CircuitsSemiconductor Fundamentals

Carrier drift current in a semiconductor is produced primarily by?

AAn applied electric field
BA carrier concentration gradient only
COptical reflection only
DA magnetic field with no electric field

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Correct Answer: A. An applied electric field

Explanation: Drift is the directed motion of charge carriers caused by an applied electric field.

Reference: Standard semiconductor electronics: drift current

Question 7

Electronic Devices & CircuitsSemiconductor Fundamentals

Carrier diffusion current arises primarily because of?

AA spatial carrier-concentration gradient
BA perfectly uniform carrier concentration
CZero temperature only
DAn ideal short circuit

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Correct Answer: A. A spatial carrier-concentration gradient

Explanation: Diffusion results from random carrier motion combined with a concentration gradient, producing net transport from higher to lower concentration.

Reference: Standard semiconductor electronics: diffusion current

Question 8

Electronic Devices & CircuitsSemiconductor Fundamentals

The Einstein relation for a nondegenerate semiconductor connects diffusion coefficient D and mobility mu approximately as?

AD/mu = kT/q
BDmu = q/kT
CD/mu = qT/k
DD = mu/T only

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Correct Answer: A. D/mu = kT/q

Explanation: The Einstein relation is D/μ = kT/q, linking carrier diffusion and drift properties at temperature T.

Reference: Standard semiconductor electronics: Einstein relation

Question 9

Electronic Devices & CircuitsSemiconductor Fundamentals

If electron mobility is 1200 cm^2/(V s) and the electric field is 10 V/cm, the low-field electron drift velocity is approximately?

A120 cm/s
B1200 cm/s
C12000 cm/s
D120000 cm/s

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Correct Answer: C. 12000 cm/s

Explanation: v_d=mu E=1200×10=12000 cm/s.

Reference: Standard semiconductor electronics: drift velocity calculation

Question 10

Electronic Devices & CircuitsSemiconductor Fundamentals

Minority-carrier diffusion length L is related to diffusion coefficient D and carrier lifetime tau by?

AL=sqrt(D tau)
BL=D/tau
CL=D tau
DL=sqrt(D/tau)

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Correct Answer: A. L=sqrt(D tau)

Explanation: The characteristic diffusion length is L=sqrt(D tau), describing the average scale over which excess minority carriers diffuse before recombination.

Reference: Standard semiconductor electronics: diffusion length

Question 11

Electronic Devices & CircuitsSemiconductor Fundamentals

In an n-type semiconductor at equilibrium, moving the Fermi level closer to the conduction band generally indicates?

AHigher electron concentration
BHigher hole concentration only
CZero carrier concentration
DAn insulating state necessarily

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Correct Answer: A. Higher electron concentration

Explanation: For nondegenerate n-type material, a Fermi level closer to the conduction band corresponds to a larger equilibrium electron concentration.

Reference: Standard semiconductor electronics: Fermi level

Question 12

Electronic Devices & CircuitsSemiconductor Fundamentals

For a semiconductor, conductivity sigma is approximately q(n mu_n + p mu_p). If electron concentration increases while mobilities and hole concentration remain unchanged, conductivity generally?

AIncreases
BDecreases
CBecomes zero
DRemains exactly unchanged

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Correct Answer: A. Increases

Explanation: The electron term q n mu_n increases with electron concentration, so total conductivity increases under the stated assumptions.

Reference: Standard semiconductor electronics: conductivity

Question 13

Electronic Devices & CircuitsSemiconductor Fundamentals

The resistivity of a homogeneous semiconductor is the reciprocal of its?

AConductivity
BMobility only
CCarrier lifetime
DBand gap only

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Correct Answer: A. Conductivity

Explanation: Electrical resistivity rho and conductivity sigma are related by rho=1/sigma.

Reference: Standard semiconductor electronics: resistivity and conductivity

Question 14

Electronic Devices & CircuitsSemiconductor Fundamentals

In a semiconductor, carrier mobility is defined as the ratio of drift velocity to?

AApplied electric field
BCarrier concentration
CDiffusion length
DJunction voltage only

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Correct Answer: A. Applied electric field

Explanation: In the low-field region, drift velocity v_d = mu E, so mobility is v_d/E.

Reference: Standard semiconductor electronics: carrier mobility