NEET P-N Junction Diode and its applications MCQs & PYQs

Q: Depletion layer has (for an unbiased PN junction): (1999)

In an unbiased p-n junction, the depletion layer is created by the natural diffusion of majority charge carriers across the junction. As mobile electrons and holes cross the boundary and recombine, they leave behind uncompensated positive and negative ions in the crystal lattice. Because these exposed ions are firmly bound to the lattice structure, they cannot move. As a result, this central region is entirely depleted of mobile charge carriers and contains only immobile, static ions.

Practice NEET P-N Junction Diode and its applications Questions

Question 41:

easy

Pure Si at 500 K has equal number of electron ($n_e$) and hole ($n_h$) concentrations of $1.5 \times 10^{16} m^{-3}$. Doping by indium increases $n_h$ to $4.5 \times 10^{22} m^{-3}$. The doped semiconductor is of:

(2011 Mains)

Using the mass action law $n_e n_h = n_i^2$, we have $n_e = \frac{n_i^2}{n_h} = \frac{(1.5 \times 10^{16})^2}{4.5 \times 10^{22}} = \frac{2.25 \times 10^{32}}{4.5 \times 10^{22}} = 0.5 \times 10^{10} = 5 \times 10^9 m^{-3}$. Indium is trivalent, so it forms a p-type semiconductor.[cite: 1]

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Question 42:

easy

The increase in the width of the depletion region in a p-n junction diode is due to :

(2020)

In reverse bias, the applied electric field aligns with the built-in electric field of the junction, pulling majority carriers away from the junction. This widens the depletion region.[cite: 1]

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Question 43:

easy

The barrier potential of a p-n junction depends on: A. Type of semiconductor material B. Amount of doping C. Temperature Which one of the following is correct?

(2014)

The built-in barrier potential $V_0 = \frac{kT}{q} \ln(\frac{N_A N_D}{n_i^2})$. This formula shows it depends on temperature $T$, doping concentrations $N_A$ and $N_D$, and intrinsic concentration $n_i$, which depends on the material.

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Question 44:

easy

In a PN junction:

(2002)

In an unbiased PN junction, immobile positive donor ions on the N-side and negative acceptor ions on the P-side form the depletion region. The electric field points from N to P, meaning the N-side is at a higher electrical potential.

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Question 45:

easy

Reverse bias applied to a junction diode:

(2003)

In reverse bias, the positive terminal is connected to the n-side and the negative terminal to the p-side. This pulls majority charge carriers away from the junction, increasing the width of the depletion layer and thereby raising the potential barrier.

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Question 46:

easy

Barrier potential of a p-n junction diode does not depend on:

(2003)

The barrier potential of a p-n junction depends on the semiconductor material, temperature, and doping concentration. It is completely independent of the physical dimensions or macroscopic design of the diode.

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Question 47:

easy

The cause of potential barrier in a P-N junction diode is:

(1998)

During the formation of a p-n junction, the diffusion of majority carriers across the junction leaves behind immobile positive donor ions on the n-side and negative acceptor ions on the p-side, establishing the potential barrier.

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Question 48:

easy

p-n junction is said to be forward biased, when

(1988)

In forward biasing, the external voltage must oppose the built-in potential. This happens when the positive terminal of the battery is connected to the p-type region and the negative terminal to the n-type region.

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Question 49:

easy

In a p-n junction diode, change in temperature due to heating

(2018)

Heating a p-n junction generates more electron-hole pairs, which changes the intrinsic carrier concentration. This significantly affects both majority and minority carriers, altering the overall V-I characteristics.

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Question 50:

easy

Depletion layer has (for an unbiased PN junction):

(1999)

In an unbiased p-n junction, the depletion layer is created by the natural diffusion of majority charge carriers across the junction. As mobile electrons and holes cross the boundary and recombine, they leave behind uncompensated positive and negative ions in the crystal lattice.

Because these exposed ions are firmly bound to the lattice structure, they cannot move. As a result, this central region is entirely depleted of mobile charge carriers and contains only immobile, static ions.

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