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 CExplaination / 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
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 AExplaination / 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, ΔpBfor base. ΔnCfor collector) normalized to equilibrium minority carrier concentration (nE0for 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 CExplaination / 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 DExplaination / 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 × 1010cm-3, What is the magnitude of the built-in potential of this device?
Q9.A region of negative differential resistance is observed in the current voltage characteristics of a silicon PN junction if
Answer : Option AExplaination / 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.