Which of the following is a direct bandgap semiconductor?
Answer: A
GaAs is a direct bandgap semiconductor where the minimum energy gap occurs at the same k-value, making it suitable for light emission. Si and Ge are indirect bandgap semiconductors.
Q.242Easy
At absolute zero temperature, the number of free electrons in an intrinsic semiconductor is:
Answer: B
At T = 0 K, all electrons remain in the valence band. No thermal energy is available to excite electrons to the conduction band, so free electrons are zero.
Q.243Easy
The bandgap of silicon at room temperature (300 K) is approximately:
Answer: B
Silicon has a bandgap of approximately 1.1 eV at 300 K. This is a standard value used in semiconductor physics and device design.
Q.244Easy
A p-type semiconductor is created by doping silicon with:
Answer: C
Boron is a Group III element (trivalent) that acts as an acceptor in silicon, creating holes and forming p-type semiconductor. Phosphorus, Arsenic, and Antimony are Group V elements (pentavalent) forming n-type semiconductors.
Q.245Easy
An LED emits light because:
Answer: A
In LEDs (forward biased p-n junctions in direct bandgap semiconductors like GaAs), electron-hole recombination releases energy as photons. Indirect bandgap materials (Si, Ge) produce mainly heat.
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Q.246Easy
In an intrinsic semiconductor at room temperature, if the bandgap energy is Eg, what is the relationship between electron and hole concentrations?
Answer: C
In an intrinsic semiconductor, the number of electrons equals the number of holes as they are generated in pairs. Both equal the intrinsic carrier concentration ni.
Q.247Easy
When a p-type semiconductor is doped with donor atoms instead of acceptors, what happens to the Fermi level position?
Answer: B
Adding donor atoms to a p-type semiconductor introduces electrons, shifting the material towards n-type behavior and moving the Fermi level toward the conduction band.
Q.248Easy
Which of the following statements about the bandgap of semiconductors is correct?
Answer: B
The bandgap energy decreases with increasing temperature at a rate of approximately -2 to -4 meV/K, described by the Varshni equation: Eg(T) = Eg(0) - αT²/(T+β)
Q.249Easy
The pinch-off voltage Vp in a JFET is the gate voltage at which:
Answer: A
At pinch-off voltage, the depletion region extends completely across the channel width, cutting off the flow of carriers and reducing drain current to nearly zero (IDSS becomes zero).
Q.250Easy
In a p-n junction diode at thermal equilibrium, the direction of the electric field in the depletion region is:
Answer: B
At thermal equilibrium, the built-in electric field points from the p-region (positive) to n-region (negative) to oppose further diffusion of carriers.
Q.251Easy
The band gap energy of Germanium at room temperature (300K) is approximately:
Answer: A
Germanium has a band gap of ~0.66 eV at room temperature, making it a narrow band gap semiconductor used in infrared applications.
Q.252Easy
When a semiconductor is doped with donor atoms, the Fermi level shifts:
Answer: B
Donor doping creates an n-type semiconductor, shifting the Fermi level closer to the conduction band due to increased electron concentration.
Q.253Easy
A zener diode is used in reverse bias to:
Answer: B
Zener diodes are operated in reverse bias within the zener breakdown region to maintain constant voltage across them, useful for voltage regulation.
Q.254Easy
In a BJT (Bipolar Junction Transistor) in active mode, the base-emitter junction is:
Answer: B
In active mode, BE junction is forward biased (injects carriers) while BC junction is reverse biased (collects carriers).
Q.255Easy
When a semiconductor is exposed to light with photon energy greater than band gap energy, the phenomenon is:
Answer: B
Photoconductivity is the increase in conductivity when photons with E > Eg create electron-hole pairs, increasing charge carrier concentration.
Q.256Easy
At room temperature (300 K), the intrinsic carrier concentration of silicon is approximately:
Answer: A
The intrinsic carrier concentration (ni) of silicon at 300 K is approximately 1.5 × 10^10 cm^-3, which is a standard value used in semiconductor calculations.
Q.257Easy
In a p-n junction at equilibrium, the potential difference across the junction is called:
Answer: B
The built-in potential (V₀) develops naturally across a p-n junction due to diffusion of charge carriers. For silicon at 300 K, V₀ ≈ 0.7 V, independent of external voltage.
Q.258Easy
In an intrinsic semiconductor at room temperature, what is the relationship between electron concentration (n_e) and hole concentration (n_h)?
Answer: B
In an intrinsic semiconductor, every electron-hole pair is generated together, so the concentration of free electrons equals the concentration of holes, both equal to the intrinsic carrier concentration n_i.
Q.259Easy
The forbidden energy gap (E_g) of germanium at 300K is approximately:
Answer: B
Germanium has a bandgap of approximately 0.66 eV at room temperature (300K), making it a narrow bandgap semiconductor compared to silicon (1.1 eV).
Q.260Easy
In a p-type semiconductor, the majority carriers are:
Answer: B
P-type semiconductors are doped with acceptor impurities which create holes as majority carriers. Electrons become minority carriers in p-type material.
