BEE FREE BEE Bachelor of Electrical Engineering Semiconductor Devices and Circuits Questions and Answers 2 — Questions and Answers
Question 1: What is the primary function of a Zener diode in a circuit?
- Voltage regulation (Correct answer)
- Signal amplification
- Current amplification
- Frequency modulation
Correct answer: Voltage regulation
A Zener diode operates in reverse breakdown to maintain a constant voltage across its terminals, making it ideal for voltage regulation.
Question 2: In a MOSFET operating in the saturation region, the drain current is primarily controlled by which parameter?
- Gate-to-source voltage (Correct answer)
- Drain-to-source voltage
- Substrate doping concentration
- Channel length only
Correct answer: Gate-to-source voltage
In saturation, the MOSFET drain current depends on the gate-to-source voltage according to the square-law relationship and is nearly independent of drain-to-source voltage.
Question 3: What phenomenon causes the collector current in a BJT to increase slightly with increasing collector-emitter voltage in the active region?
- Early effect (Correct answer)
- Avalanche breakdown
- Kirk effect
- Thermal runaway
Correct answer: Early effect
The Early effect (base-width modulation) causes the effective base width to narrow as VCE increases, slightly increasing collector current.
Question 4: Which type of semiconductor recombination involves the emission of a photon?
- Radiative recombination (Correct answer)
- Auger recombination
- Shockley-Read-Hall recombination
- Surface recombination
Correct answer: Radiative recombination
Radiative recombination occurs when an electron and hole recombine directly, releasing energy as a photon, which is the basis of LED operation.
Question 5: What is the cutoff frequency of a common-emitter BJT amplifier primarily limited by?
- Junction capacitances and transit time (Correct answer)
- Power supply voltage
- Load resistance
- Base doping concentration
Correct answer: Junction capacitances and transit time
The cutoff frequency is limited by the base-emitter and base-collector junction capacitances combined with carrier transit time through the base.
Question 6: In a p-n junction solar cell, what generates the photocurrent?
- Electron-hole pairs created in or near the depletion region (Correct answer)
- Majority carrier drift in the bulk
- Tunneling through the junction barrier
- Thermionic emission over the barrier
Correct answer: Electron-hole pairs created in or near the depletion region
Photons absorbed in or near the depletion region create electron-hole pairs that are swept by the built-in electric field, producing photocurrent.
BEE FREE BEE Bachelor of Electrical Engineering Semiconductor Devices and Circuits Questions and Answers 2
What is the primary function of a Zener diode in a circuit?