Semiconductor Energy Bands and Carrier Statistics - Electronic Devices - Electronics & Communication Engineering Previous Year Questions

1

2008 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2008

Which of the following is true?

A

A silicon wafer heavily doped with boron is a \(p^+\) substrate

B

A silicon wafer lightly doped with boron is a \(p^+\) substrate

C

A silicon wafer heavily doped with arsenic is a \(p^+\) substrate

D

A silicon wafer lightly doped with arsenic is a \(p^+\) substrate

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2

2008 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2008

Silicon is doped with boron to a concentration of $4 \times 10^{17}$ atoms/cm³. Assume the intrinsic carrier concentration of silicon to be $1.5 \times 10^{10}$/cm³ and the value of $\frac{kT}{q}$ to be 25 mV at 300 K. Compared to undoped silicon, the Fermi level of doped silicon

A

goes down by 0.13 eV

B

goes up by 0.13 eV

C

goes down by 0.427 eV

D

goes up by 0.427 eV

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3

2009 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2009

In an n-type silicon crystal at room temperature, which of the following can have a concentration of \(4 \times 10^{19} \text{ cm}^{-3}\) ?

A

Silicon atoms

B

Holes

C

Dopant atoms

D

Valence electrons

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4

2012 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2012

The source of a silicon (\( n_i = 10^{10} \) per \( cm^3 \)) n-channel MOS transistor has an area of 1 sq \( \mu m \) and a depth of 1 \( \mu m \). If the dopant density in the source is \( 10^{19}/cm^3 \), the number of holes in the source region with the above volume is approximately

A

\(10^7 \)

B

100

C

10

D

0

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5

2014 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2014 [Session 4]

An N-type semiconductor having uniform doping is biased as shown in the figure.
If E_C is the lowest energy level of the conduction band, E_V is the highest energy level of the valance band and E_F is the Fermi level, which one of the following represents the energy band diagram for the biased N-type semiconductor?

A

Option A diagram

B

Option B diagram

C

Option C diagram

D

Option D diagram

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6

2014 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2014 [Session 4]

At T = 300 K, the band gap and the intrinsic carrier concentration of GaAs are 1.42 eV and \(10^6\) cm\(^{-3}\), respectively. In order to generate electron hole pairs in GaAs, which one of the wavelength (\(\lambda_c\)) ranges of incident radiation, is most suitable? (Given that: Plank's constant is \(6.62 \times 10^{-34}\) J-s, velocity of light is \(3 \times 10^{10}\) cm/s and charge of electron is \(1.6 \times 10^{-19}\) C)

A

0.42 \(\mu m < \lambda_c <\) 0.87 \(\mu m\)

B

0.87 \(\mu m < \lambda_c <\) 1.42 \(\mu m\)

C

1.42 \(\mu m < \lambda_c <\) 1.62 \(\mu m\)

D

1.62 \(\mu m < \lambda_c <\) 6.62 \(\mu m\)

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7

2016 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2016 [Session 1]

A small percentage of impurity is added to an intrinsic semiconductor at 300 K. Which one of the following statements is true for the energy band diagram shown in the following figure?

A

Intrinsic semiconductor doped with pentavalent atoms to form n-type semiconductor

B

Intrinsic semiconductor doped with trivalent atoms to form n-type semiconductor

C

Intrinsic semiconductor doped with pentavalent atoms to form p-type semiconductor

D

Intrinsic semiconductor doped with trivalent atoms to form p-type semiconductor

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8

2020 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2020

A single crystal intrinsic semiconductor is at a temperature of 300 K with effective density of states for holes twice that of electrons. The thermal voltage is 26 mV. The intrinsic Fermi level is shifted from mid-bandgap energy level by

A

18.02 meV.

B

9.01 meV.

C

13.45 meV.

D

26.90 meV.

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9

2021 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2021

The energy band diagram of a p-type semiconductor bar of length \(L\) under equilibrium condition (i.e., the Fermi energy level \(E_F\) is constant) is shown in the figure. The valence band \(E_V\) is sloped since doping is non-uniform along the bar. The difference between the energy levels of the valence band at the two edges of the bar is \(\Delta\).
If the charge of an electron is \(q\), then the magnitude of the electric field developed inside this semiconductor bar is

A

\(\frac{\Delta}{qL} \)

B

\(\frac{2\Delta}{qL} \)

C

\(\frac{\Delta}{2qL} \)

D

\(\frac{3\Delta}{2qL} \)

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10

2022 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2022

In a non-degenerate bulk semiconductor with electron density \(n = 10^{16} \text{ cm}^{-3}\), the value of \(E_C - E_{Fn} = 200 \text{ meV}\), where \(E_C\) and \(E_{Fn}\) denote the bottom of the conduction band energy and electron Fermi level energy, respectively. Assume thermal voltage as 26 meV and the intrinsic carrier concentration is \(10^{10} \text{ cm}^{-3}\). For \(n = 0.5 \times 10^{16} \text{ cm}^{-3}\), the closest approximation of the value of \((E_C - E_{Fn})\), among the given options, is ________.

A

226 meV

B

174 meV

C

218 meV

D

182 meV

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11

2023 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2023

In a semiconductor, if the Fermi energy level lies in the conduction band, then the semiconductor is known as

A

degenerate n-type.

B

degenerate p-type.

C

non-degenerate n-type.

D

non-degenerate p-type.

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12

2023 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2023

For an intrinsic semiconductor at temperature \( T = 0 K \), which of the following statement is true?

A

All energy states in the valence band are filled with electrons and all energy states in the conduction band are empty of electrons.

B

All energy states in the valence band are empty of electrons and all energy states in the conduction band are filled with electrons.

C

All energy states in the valence and conduction band are filled with holes.

D

All energy states in the valence and conduction band are filled with electrons.

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13

2023 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2023

In a semiconductor device, the Fermi-level energy is 0.35 eV above the valence band energy. The effective density of states in the valence band at \(T = 300\) K is \(1 \times 10^{19} cm^{-3}\). The thermal equilibrium hole concentration in silicon at 400 K is ______ \(\times 10^{13} cm^{-3}\) (rounded off to two decimal places). Given \(kT\) at 300 K is 0.026 eV.

Check answer

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14

2024 · Electronics & Communication Engineering · Electronic Devices · Semiconductor Energy Bands and Carrier Statistics

Electronics & Communication Engineering (EC) 2024

For non-degenerately doped n-type silicon, which one of the following plots represents the temperature (\( T \)) dependence of free electron concentration (\( n \))?

A

Plot A: log(n) vs 1/T, starts high, drops, then plateaus, then drops at high 1/T

B

Plot B: log(n) vs 1/T, constant horizontal line

C

Plot C: log(n) vs 1/T, starts flat, then drops at high 1/T

D

Plot D: log(n) vs 1/T, straight line with negative slope

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