Physics

Semiconductors and Diodes

461 Questions

Semiconductors and diodes form the foundation of modern electronics, covering topics like intrinsic carrier concentration and Zener breakdown. Questions often explore the characteristics of bipolar junction transistors (BJT) and the properties of doped silicon materials. This topic is crucial for physics and electronics engineering competitive exams.

Zener diode breakdownBJT circuit analysisIntrinsic carrier concentrationDoping in semiconductorsEmitter follower circuit

Semiconductors and Diodes Questions

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Statement-I  The conductance through electrons is called n-type conduction and if through positive semi holes it is called p-type conduction.

Statement-II  Doping involves the preparation of semiconductor by the addition of impurities in the intrinsic semiconductor.

  1. Statement-I is correct but Statement-II is wrong

  2. Statement-I is wrong but Statement-II is correct

  3. Both Statement-I and Statement-II are correct and Statement-II is correct explanation of Statement-I

  4. Both Statement-I and Statement-II are correct but Statement-II is not correct explanation of Statement-I
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The conductance through electrons is called n-type conduction and if through positive semiholes, it is called p-type conduction.
Doping involves preparation of semi-conductors by the presence of impurities in the intrinsic semiconductor.With donor impurities, we get n-type semi-conductors and with acceptor impurities, we get p-type semi-conductors.

Thus, the explanation provided was inadequate.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Select the correct statement(s).

  1. The conductance through electrons is called p-type conduction.

  2. The conductance through positive holes is called p-type conduction.

  3. The conductance through electrons is called n-type conduction.

  4. The band gap in germanium is small.
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation

The addition of small amount of foreign impurity in the host crystal is called as doping. It results in an increase in the electrical conductivity of the crystal. Doping of group 14 elements (such as Si, Ge etc.) with elements of group 15 (such as As) produces an excess of electrons in the crystals and thus, gives n-type semiconductors. Doping of groups 14 elements with group 13 elements (such as Indium) produces holes (electron deficiency) in the crystals. Thus, p-type semiconductors are produced. The symbol 'p' indicates flow of positive charge. Also, the band gap in germanium is small as Ge is a semi-conductor.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Assertion: 

Group-$15$ doped crystals of Si are called n-type semiconductors.
Reason: 
Neutrons are responsible for the semiconducting properties.

  1. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

  3. Assertion is correct but Reason is incorrect

  4. Assertion is incorrect but Reason is correct

  5. Both Assertion and Reason are incorrect
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The addition of a small amount of foreign impurity in the host crystal is called doping. 

It increases the electrical conductivity of the crystal. Doping of group 14 elements (such as Si, Ge, etc.) with elements of group 15 (such as As) produces an excess of electrons in the crystals, thus, giving n-type semiconductors. 
Doping of groups 14 elements with group 13 elements (such as Indium) produces holes (electron deficiency) in the crystals. Thus, p-type semiconductors are produced. The symbol 'p' indicates the flow of positive charge.

Thus, Assertion is correct but Reason is incorrect

Hence, the correct option is $\text{C}$

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Assertion: Group-$13$ doped crystals of Si are called p-type semiconductors.
Reason: Positive holes are responsible for the semiconducting properties.

  1. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

  3. Assertion is correct but Reason is not correct

  4. Assertion is not correct but Reason is correct

  5. Both Assertion and Reason are incorrect
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The addition of small amount of foreign impurity in the host crystal is called as doping. It results in an increase in the electrical conductivity of the crystal. Doping of group 14 elements (such as Si, Ge etc.) with elements of group 15 (such as As) produces an excess of electrons in the crystals, thus, giving n-type semiconductors. Doping of groups 14 elements with group 13 elements (such as Indium) produces holes (electron deficiency) in the crystals. Thus, p-type semiconductors are produced. The symbol 'p' indicates flow of positive charge. Positive holes are responsible for the semiconducting properties like conduction.

Multiple choice physics electric current drift velocity and mobility drift speed drift velocity & mobility

In semiconductor the concentrations of electrons and holes are $8 \times 10 ^ { 18 } / \mathrm { m } ^ { 3 }$and $5 \times 10 ^ { 8 } / \mathrm { m } ^ { 3 }$ respectively.If the mobilities of electrons and holes are 2.3$\mathrm { m } ^ { 2 } / \mathrm { Vs }$ and 0.01$\mathrm { m } ^ { 2 } / \mathrm { Vs }$ respectively then semi conductor is

  1. N-type with resistivity $0.34 \Omega - \mathrm { m }$
  2. P-type with resistivity $0.34 \Omega - \mathrm { m }$
  3. N-type with resistivity $0.034 \Omega - \mathrm { m }$
  4. P-type with resistivity $3.4 \Omega - \mathrm { m }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than $2480\ nm$ is incident on it. The band gap in $(eV)$ for the semiconductor is.

  1. $0.5\ eV$
  2. $0.7\ eV$
  3. $1.1\ eV$
  4. $2.5\ eV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The band gap energy E = hc / lambda. Using h = 6.63e-34, c = 3e8, and lambda = 2480e-9 m, E = 1240 eV nm / 2480 nm = 0.5 eV.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

In extrinsic semiconductors :

  1. the conduction band and valence band overlap
  2. the gap between conduction band and valence band is near about $16\ eV$
  3. the gap between conduction band and valence band is near about $ 1\ eV$
  4. the gap between conduction band and valence band will be $100\ eV$ and more
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In extrinsic semiconductors, formation of donor or acceptor level takes place in forbidden energy gap. Thus, some of the electrons in valance band acquire enough energy to jump to donor level or acceptor level present in forbidden energy gap. Thus, to obtain large number of electrons in conduction band some energy to be supplied to the electrons in valance band. For extrinsic semiconductors, it is nearly equal to $1\ eV$.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

The energy gap in a semiconductor 

  1. Increases with temperature

  2. Does not change with temperature

  3. Decreases with temperature

  4. Is zero
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The energy bandgap of semiconductors tends to decrease as the temperature is increased.  the interatomic spacing increases when the amplitude of the atomic vibrations increases due to the increased thermal energy. This effect is quantified by the linear expansion coefficient of a material. An increased interatomic spacing decreases the potential seen by the electrons in the material, which in turn reduces the size of the energy bandgap. A direct modulation of the interatomic distance, such as by applying high compressive (tensile) stress, also causes an increase (decrease) of the bandgap.

The variance of energy gap with temperature is given by
$E _g(T)=E _g(0)-\dfrac{\alpha T^2}{T+\beta}$

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

What is the optimum band gap energy for a material to be considered as a semiconductor?

  1. greater than $6eV$
  2. less than $6eV$
  3. $0eV$
  4. $0.5-3eV$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Semiconductor materials have low but finite band gap energy, due to which there is an easy jump of electron from valence band to conduction band upon provision of external thermal energy.

The typical range of band gap energy for a semiconductor material is $0.5eV-3eV$.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

Choose the correct statement(s):

  1. Band gap of a semiconductor increases as temperature increases.

  2. Band gap of a semiconductor decreases as the temperature increases.

  3. Band gap of a semiconductor is independent of temperature.

  4. Bandgap of a semiconductor decreases till critical temperature and increases after that.

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The energy bandgap of semiconductors tends to decrease as the temperature is increased. This behaviour can be understood if one considers that the interatomic spacing increases when the amplitude of the atomic vibrations increases due to the increased thermal energy. This effect is quantified by the linear expansion coefficient of a material. An increased interatomic spacing decreases the potential seen by the electrons in the material, which in turn reduces the size of the energy bandgap. 

This is the reason behind the decrease in resistance of semiconductor materials by increasing temperature.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

What is the energy band gap of silicon and germanium respectively in $eV$  ?

  1. $1.1, 0.7$
  2. $0.7, 1.1$
  3. $-0.7, -1.1$
  4. $-1.1, -0.7$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A band gap, also called an energy band, is an energy range in a solid where no electron states can exist. It generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. The energy band gaps of silicon and germanium are $1.1eV $ and $0.7eV$ respectively.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

 Fermi energy level for $p-type$ extrinsic semiconductors lies 

  1. At middle of the band gap

  2. Close to conduction band

  3. Close to valence band

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In case of a p-type semiconductor, the number of holes in valence band is grater then number of electrons in conduction band. hence, the probability of occupation of energy levels by the holes in valence band is greater than probability of occupation of energy levels by electrons in conduction band. This probability of occupation of energy levels is represented in terms of Fermi level.

$\therefore $ female level in p-type semiconductor lies does to valence band.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

Fermi energy level for intrinsic semiconductors lies 

  1. At middle of the band gap

  2. Close to valence band

  3. Close to conduction band

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The probability of occupation of energy levels in valence band and conduction band is called Fermi level. As the temperature increases free electrons and holes gets generated. In intrinsic semiconductor, the number of holes in valence band is equal to the number of electrons in the conduction band. Hence, the probability of occupation of energy levels in conduction band and valence band are equal. Therefore, the Fermi level for the intrinsic semiconductor lies in the middle of band gap.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

Energy gap of semiconductor is approx

  1. $1 eV$
  2. $0 \ eV$
  3. $6-7 eV$
  4. $> 8\ eV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The energy gap of a semiconductor lies in between insulators and conductors. In case of conductors, band gap Eg $\sim 0$ eV. Whereas in case of insulators, Eg $\sim 3-4$ eV. So, Band gap in case of a semiconductor is of order $\sim 1$ eV.

Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

The level formed due to impurity atom, in the forbidden energy gap, very near to the valence band in a P-type semiconductor is called

  1. an acceptor level

  2. a donor level

  3. a conduction level

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The level formed due to impurity atom, in the forbidden energy gap, very near to the valency band in a p-type semiconductor is called an acceptor level.

The level formed due to impurity atom, in the forbidden energy gap, very near to the conduction band in a p-type semiconductor is called a donor level.
Therefore option $A$ is correct.