ISCET Semiconductor Device Principles 2 — Questions and Answers
Question 1: What is the primary effect of increasing temperature on the reverse saturation current (I₀) of a silicon diode?
- I₀ decreases exponentially
- I₀ approximately doubles for every 10°C rise (Correct answer)
- I₀ remains constant
- I₀ decreases linearly
Correct answer: I₀ approximately doubles for every 10°C rise
Reverse saturation current approximately doubles for every 10°C increase in temperature due to increased minority carrier generation.
Question 2: In a PNP bipolar junction transistor operating in active mode, the emitter current is 10 mA and the base current is 0.2 mA. What is the collector current?
- 10.2 mA
- 9.8 mA (Correct answer)
- 0.2 mA
- 50 mA
Correct answer: 9.8 mA
By KCL, IC = IE – IB = 10 mA – 0.2 mA = 9.8 mA.
Question 3: Which semiconductor parameter defines the average time a minority carrier exists before recombining?
- Mobility
- Diffusion length
- Minority carrier lifetime (Correct answer)
- Transit time
Correct answer: Minority carrier lifetime
Minority carrier lifetime (τ) is the average time a minority carrier survives before recombining with a majority carrier.
Question 4: A Zener diode is used primarily in which region of its V-I characteristic?
- Forward bias above 0.7 V
- Reverse bias below the breakdown voltage
- At the Zener breakdown voltage (Correct answer)
- In the depletion region only
Correct answer: At the Zener breakdown voltage
Zener diodes are designed to operate at the reverse breakdown (Zener) voltage, maintaining a stable reference voltage.
Question 5: What is the typical value of the Early voltage (VA) for a small-signal BJT, and what does a larger VA indicate?
- Typically 5–10 V; larger VA means more output resistance variation
- Typically 50–200 V; larger VA means higher output resistance and less channel-length modulation (Correct answer)
- Typically 0.7 V; larger VA means the transistor saturates sooner
- Typically 1 kV; larger VA means lower gain
Correct answer: Typically 50–200 V; larger VA means higher output resistance and less channel-length modulation
Early voltage is typically 50–200 V for BJTs; a higher VA means the output characteristics are more horizontal, indicating higher output resistance.
Question 6: In an N-channel JFET, what happens to the drain current when the gate-to-source voltage (VGS) is made more negative?
- Drain current increases
- Drain current decreases toward zero (Correct answer)
- Drain current remains constant
- Drain current reverses direction
Correct answer: Drain current decreases toward zero
Making VGS more negative widens the depletion region in the N-channel JFET, constricting the channel and reducing drain current toward IDSS cutoff.
Question 7: Which effect describes the increase in BJT collector current due to base-width narrowing as VCE increases?
- Miller effect
- Early effect (Correct answer)
- Punch-through effect
- Kirk effect
Correct answer: Early effect
The Early effect (base-width modulation) causes collector current to increase slightly as VCE increases, narrowing the neutral base width.
ISCET Semiconductor Device Principles 2
What is the primary effect of increasing temperature on the reverse saturation current (I₀) of a silicon diode?