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.42Easy
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.43Easy
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.44Medium
The temperature coefficient of resistance for semiconductors is:
Answer: B
Semiconductors have negative temperature coefficient because increased temperature increases intrinsic carrier concentration, decreasing resistance.
Q.45Medium
In a metal-semiconductor contact, if the metal work function is greater than the semiconductor work function, a __________ barrier is formed:
Answer: A
When metal work function > semiconductor work function, electrons transfer from semiconductor to metal, creating a Schottky barrier.
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Q.46Easy
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.47Medium
In an LED, the wavelength of emitted light depends on:
Answer: B
The energy of emitted photons equals the band gap energy (E = Eg = hc/λ), determining the color/wavelength of LED light.
Q.48Medium
The Hall coefficient for a p-type semiconductor is:
Answer: A
Hall coefficient is positive for p-type (hole conduction) and negative for n-type (electron conduction), based on the sign of majority carriers.
Q.49Easy
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.50Medium
The transconductance (gm) of a MOSFET increases with:
Answer: A
Transconductance gm ∝ W/L (width-to-length ratio), so decreasing channel length L increases transconductance.
Q.51Medium
A solar cell's efficiency is reduced by all the following EXCEPT:
Answer: C
Increasing minority carrier lifetime improves efficiency by reducing recombination losses. Other options reduce efficiency.
Q.52Hard
In a tunnel diode, negative differential resistance occurs because:
Answer: C
In tunnel diode's NDR region, as voltage increases, tunneling current decreases (fewer states to tunnel into) while diffusion current increases, causing net decrease in total current.
Q.53Medium
The output impedance of a common-emitter amplifier is determined primarily by:
Answer: A
Output impedance Zo ≈ Rc || RL (Rc in parallel with load resistance), depending on collector circuit configuration.
Q.54Easy
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.55Hard
The current gain (β) of a BJT at constant IC depends on:
Answer: B
β varies with temperature and VBE changes, following the Ebers-Moll model. Early voltage causes slight VCE dependence.
Q.56Medium
In a MOSFET, the threshold voltage VT is defined as the gate voltage at which:
Answer: B
Threshold voltage VT is when the surface band bending creates an inversion layer, transition from depletion to strong inversion.
Q.57Hard
The noise figure of a semiconductor amplifier is lowest when operating at:
Answer: B
Minimum noise figure occurs at optimum source impedance that matches the device's noise characteristics, typically provided in device specifications.
Q.58Medium
In a p-n junction under reverse bias, the depletion width increases because:
Answer: A
Reverse bias voltage adds to the built-in potential, increasing the total electric field and widening the depletion region further.
Q.59Hard
The Shockley ideal diode equation predicts that reverse saturation current (Is) is proportional to:
Answer: C
Is ∝ ni²/(NA·ND), depending on intrinsic carrier concentration squared and inversely on doping concentrations.
Q.60Easy
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.
