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16
MCQ (Multiple Correct Answer)

The breakdown in a reverse biased $p-n$ junction is more likely to occur due to

A
large velocity of the minority charge carriers if the doping concentration is small
B
large velocity of the minority charge carriers if the doping concentration is large
C
strong electric field in a depletion region if the doping concentration is small
D
strong electric field in the depletion region if the doping concentration is large
17
Subjective

Why are elemental dopants for Silicon or Germanium usually chosen from group XIII or group XV?

Explanation

The size of the dopant atom should be such that their presence in the pure semiconductor does not distort the semiconductor but easily contribute the charge carriers on forming covalent bonds with Si or Ge atoms, which are provided by group XIII or group XV elements.

18
Subjective

$\mathrm{Sn}, \mathrm{C}$ and $\mathrm{Si}, \mathrm{Ge}$ are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why?

Explanation

A material is a conductor if in its energy band diagram, there is no energy gap between conduction band and valence band. For insulator, the energy gap is large and for semiconductor the energy gap is moderate.

The energy gap for Sn is 0 eV, for C is 5.4 eV , for Si is 1.1 eV and for Ge is 0.7 eV , related to their atomic size. Therefore Sn is a conductor, C is an insulator and Ge and Si are semiconductors.

19
Subjective

Can the potential barrier across a $p-n$ junction be measured by simply connecting a voltmeter across the junction?

Explanation

We cannot measure the potential barrier across a $p-n$ junction by a voltmeter because the resistance of voltmeter is very high as compared to the junction resistance.

20
Subjective

Draw the output waveform across the resistor in the given figure.

Explanation

As we know that the diode only works in forward biased, so the output is obtained only when positive input is given, so the output waveform is