Electronic Devices - Online Test
Q1.
Compared to a p-n junction with NA = ND = 10-14/cm3, which one of the following statements is TRUE for a p-n junction with NA = ND = 10-20/cm3?
Answer : Option C
Explaination / Solution:
Reverse bias breakdown or Zener effect occurs in highly doped PN junction through tunneling mechanism. In a highly doped PN junction, the conduction and valence bands on opposite sides of the junction are sufficiently close during reverse bias that electron may tunnel directly from the valence band on the p-side into the conduction band on n-side.
Breakdown voltage 
So, breakdown voltage decreases as concentration increases
Depletion capacitance
Depletion capacitance increases as concentration increases
Q2.
The ratio of the mobility to the diffusion coefficient in a semiconductor has the units
Answer : Option A
Explaination / Solution:
Q3. 
Consider the common emitter amplifier shown below with the following circuit parameters:
The lower cut-off frequency due to C2 is
Answer : Option B
Explaination / Solution:
Cut-off frequency due to C2
Lower cut-off frequency
Q4. A bar of Gallium Arsenide (GaAs) is doped with Silicon such that the Silicon atoms occupy Gallium and Arsenic sites in the GaAs crystal. Which one of the following statement is true?
Answer : Option A
Explaination / Solution:
Silicon atoms act as P- type dopants in Arsenic sites and n- type dopants in Gallium sites.
Q5. For a narrow base PNP BJT, the excess minority carrier concentration (ΔnE for emitter, ΔpB for base. ΔnC for collector) normalized to equilibrium minority carrier concentration (nE0 for emitter, pB0 for base, nC0 for collector) in the quasi-neutral emitter, base and collector regions are shown below. Which one of the following biasing modes is the transistor operating in?
Answer : Option C
Explaination / Solution:
As per the change carrier profile, base – to – emitter junction is reverse bias and base to collector junction is forward bias, so it works in Inverse active.
Q6. The Miller effect in the context of a Common Emitter amplifier explains
Answer : Option D
Explaination / Solution:
Miller effect increase input capacitance, so that there will be decrease in gain in the high frequency cutoff frequency.
Q7. An n+ - n Silicon device is fabricated with uniform and non-degenerate donor doping concentrations of ND1 = 1 × 1018
cm-3 and ND2 = 1 × 1015
cm-3 corresponding to the n+ and n regions respectively. At the operational temperature T, assume complete impurity ionization, kT/q = 25 mV, and intrinsic carrier concentration to be ni = 1 × 1010 cm-3, What is the magnitude of the built-in potential of this device?
Answer : Option D
Explaination / Solution:
Q8. A good transconductance amplifier should have
Answer : Option C
Explaination / Solution:
A good trans conductance amplifier should have high input and output resistance.
Q9. A region of negative differential resistance is observed in the current voltage characteristics of a silicon PN junction if
Answer : Option A
Explaination / Solution:
In case of Tunnel diode formed by PN junction, tunnel diode gives negative resistance and works in forward bias, and in tunnel diode both N and P regions are heavily doped.
Q10. For the circuit with ideal diodes shown in the figure, the shape of the output (Vout) for the given sine wave input (Vin) will be
Answer : Option C
Explaination / Solution:
For positive half A1, we have
Vout = - Vin
For negative half A2, both diode will be OFF.
So, Vout = 0
Hence, the output is obtained as
