Question About During forward biasing of a p-n junction diode, the

current is mainly due to drifting of majority carriers.

current is mainly due to drifting of minority carriers.

current is of the order of 1 A.

Comprehension

A p-type or n-type semiconductor can be converted into a p-n junction by doping it with suitable impurity. The motion of majority charge carriers causes diffusion current across the junction while the barrier electric field causes motion of minority carriers for drift current. In case of unbiased diode, the diffusion and drift currents are equal. This equilibrium is disturbed by the biasing batteries. Diodes, therefore, allow currents in one direction. This property of diode is used in making rectifiers.

Question: 1

Silicon is doped with which of the following to obtain p-type semiconductor?

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Remember the basic rule: \[ \text{Trivalent impurity} \Rightarrow \text{p-type semiconductor} \] \[ \text{Pentavalent impurity} \Rightarrow \text{n-type semiconductor} \] Boron is the most common trivalent impurity used in silicon.

Updated On: Jul 2, 2026

Phosphorus
Arsenic
Boron
Antimony

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The Correct Option is C

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Question: 2

A semiconductor has an electron concentration of \[ 5 \times 10^{22}\,\text{m}^{-3}. \] The concentration of holes is:

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For semiconductors in equilibrium: \[ np=n_i^2 \] If one carrier concentration increases, the other decreases proportionally. This formula is frequently used in board examinations and competitive exams.

Updated On: Jul 2, 2026

\[5 \times 10^{22}\,\text{m}^{-3}\]
\[1.5 \times 10^{6}\,\text{m}^{-3}\]
\[9 \times 10^{8}\,\text{m}^{-3}\]
\[4.5 \times 10^{9}\,\text{m}^{-3}\]

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The Correct Option is D

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Question: 3

During forward biasing of a p-n junction diode, the

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Remember: \[ \text{Forward Bias} \Rightarrow \text{Majority Carrier Current} \] \[ \text{Reverse Bias} \Rightarrow \text{Minority Carrier Current} \] Most questions on p-n junctions can be solved by identifying which carriers dominate the conduction process.

Updated On: Jul 2, 2026

current is mainly due to drifting of majority carriers.
current is mainly due to drifting of minority carriers.
diffusion and drift currents are equal.
current is of the order of 1 A.

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The Correct Option is A

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Question: 4

The threshold voltage for silicon diode is about

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A very common board-exam fact: \[ \text{Germanium Diode} \rightarrow 0.3\,V \] \[ \text{Silicon Diode} \rightarrow 0.7\,V \] Students should memorize these values because they are frequently used in numerical and conceptual questions.

Updated On: Jul 2, 2026

0.2 V
0.5 V
0.7 V
1.5 V

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The Correct Option is C

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Question: 5

When we dope Ge with a pentavalent element, four of its electrons bond with four germanium neighbours but fifth electron remains weakly bound. The ionisation energy for this electron is about

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In donor-doped semiconductors, the extra electron is very loosely bound because the donor energy level lies very close to the conduction band. For germanium: \[ E_D \approx 0.01\,\text{eV} \] Hence, even room-temperature thermal energy is sufficient to free most donor electrons and make them available for conduction.

Updated On: Jul 2, 2026