BEE Semiconductor Devices and Electronics 2 — Questions and Answers
Question 1: In a p-n junction diode under forward bias, the depletion region width:
- Increases
- Decreases (Correct answer)
- Remains unchanged
- First increases then decreases
Correct answer: Decreases
Forward bias reduces the built-in electric field, causing the depletion region to narrow.
Question 2: The Early effect in a BJT refers to:
- Base width modulation due to collector-base voltage (Correct answer)
- Emitter injection efficiency variation
- Thermal runaway at high currents
- Punch-through at high base currents
Correct answer: Base width modulation due to collector-base voltage
The Early effect describes how increasing collector-base reverse bias narrows the base width, increasing collector current.
Question 3: Which parameter describes the ratio of drain current change to gate-source voltage change in a MOSFET?
- Output resistance
- Transconductance (gm) (Correct answer)
- Threshold voltage
- Channel length modulation
Correct answer: Transconductance (gm)
Transconductance gm = ∂ID/∂VGS quantifies how effectively gate voltage controls drain current.
Question 4: A Zener diode is primarily used in which region of its I-V characteristic?
- Forward bias active region
- Reverse breakdown region (Correct answer)
- Forward saturation region
- Reverse leakage region
Correct answer: Reverse breakdown region
Zener diodes are designed to operate in reverse breakdown, maintaining a nearly constant voltage.
Question 5: In an n-channel JFET, pinch-off occurs when the gate-source voltage VGS equals:
- Zero volts
- The threshold voltage VT
- The pinch-off voltage VP (negative) (Correct answer)
- The supply voltage VDD
Correct answer: The pinch-off voltage VP (negative)
Pinch-off in a JFET occurs when VGS equals the negative pinch-off voltage VP, fully depleting the channel.
Question 6: The minority carrier lifetime in a semiconductor determines:
- The majority carrier drift velocity
- How long excess carriers exist before recombination (Correct answer)
- The bandgap energy
- The doping concentration
Correct answer: How long excess carriers exist before recombination
Minority carrier lifetime τ is the average time excess minority carriers survive before recombining with majority carriers.
Question 7: Which type of transistor configuration provides both current gain and voltage gain?
- Common base
- Common collector
- Common emitter (Correct answer)
- Common gate
Correct answer: Common emitter
The common emitter configuration provides both voltage gain (>1) and current gain (β), making it most widely used for amplification.
BEE Semiconductor Devices and Electronics 2
In a p-n junction diode under forward bias, the depletion region width: