Semiconductor Electronics — Previous-Year Questions

Q1. Energy gap in silicon at room temperature is approximately:

Q2. In a conductor, the valence and conduction bands:

Q3. When temperature increases, conductivity of a semiconductor:

Q4. Which has the LARGEST band gap?

Q5. Intrinsic carrier density n_i depends on temperature as:

Q1. Resistivity of a typical metal vs semiconductor differs by roughly:

Q2. Conductivity of a metal vs temperature:

Q3. A material at room temperature has resistivity 10⁻² Ω·m. Most likely:

Q4. Why is diamond an insulator while graphite is a conductor?

Q5. Semiconductors are useful because:

Q1. In an intrinsic semiconductor at T > 0 K:

Q2. Intrinsic carrier density at room temperature in Si:

Q3. If temperature doubles, intrinsic conductivity:

Q4. Mass-action law n·p = n_i² holds:

Q5. At absolute zero, an intrinsic semiconductor behaves as:

Q1. Silicon doped with phosphorus becomes:

Q2. Majority carriers in a p-type semiconductor are:

Q3. If n-Si has N_D = 10¹⁶/cm³ donors (all ionized), minority carrier (hole) concentration:

Q4. Why does even tiny doping change conductivity so dramatically?

Q5. An n-type semiconductor is electrically:

Q1. In a p-n junction at zero bias:

Q2. Typical built-in potential of a Si p-n junction:

Q3. Forward biasing a p-n junction means:

Q4. Under reverse bias, the depletion region:

Q5. Shockley diode equation predicts current is:

Q1. Threshold voltage of a silicon diode is approximately:

Q2. In reverse bias, the diode current is:

Q3. Dynamic resistance of a diode at 1 mA forward bias is approximately:

Q4. Ideal diode I-V curve:

Q5. Why does forward current of a diode rise exponentially?

Q1. DC output voltage of an ideal half-wave rectifier with V_m = 100 V input:

Q2. Peak inverse voltage (PIV) for half-wave rectifier (V_m input):

Q3. Output frequency of half-wave rectifier of 50 Hz AC:

Q4. Half-wave rectifier efficiency is at most:

Q5. Ripple factor of half-wave rectifier is:

Q1. Output frequency of a full-wave rectifier of 50 Hz input:

Q2. DC voltage from a full-wave rectifier with V_m = 50 V:

Q3. Ripple factor of full-wave rectifier:

Q4. PIV for a bridge rectifier with V_m peak input:

Q5. Why is a bridge rectifier preferred over centre-tap?

Q1. In a BJT operating in active mode:

Q2. Current gain β of a transistor is 99. Corresponding α:

Q3. Common-Emitter amplifier has voltage gain:

Q4. BJT used as a switch is in:

Q5. Emitter is heavily doped because:

Q1. AND gate output Y for inputs (A, B) = (1, 0):

Q2. Which is a UNIVERSAL gate?

Q3. XOR gate outputs 1 when:

Q4. DeMorgan's law: (A·B)' equals:

Q5. NOR gate output for (A, B) = (0, 0):

Q1. A Zener diode is used as a voltage regulator. It operates in:

Q2. If V_in = 15 V, V_Z = 9 V, R_S = 100 Ω, and load draws 30 mA, Zener current is:

Q3. A Zener diode connected without a series resistor (just across a battery > V_Z) will:

Q4. Zener breakdown is the dominant mechanism for V_Z:

Q5. Power dissipated in a Zener at V_Z = 5.6 V and I_Z = 50 mA:

Q1. An LED emits red light at ~620 nm. Its band gap is approximately:

Q2. Why are LEDs typically made of GaAs and not Si?

Q3. Forward voltage of a blue LED is typically:

Q4. An LED needs 20 mA at 2.0 V. Series resistor from a 5 V supply:

Q5. Power dissipated in the LED above: