Tag: band theory of solids, a brief introduction

Quizzes (0) Questions (63)

Questions Related to band theory of solids, a brief introduction

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

Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to $(E _g) _C,\, (E _g) _{Si}$ and $(E _g) _{Ge}$.Which of the following statements is true?

  1. $(E _g) _{Si}\, <\, (E _g) _{Ge}\, <\, (E _g) _C$

  2. $(E _g) _{C}\, <\, (E _g) _{Ge}\, >\, (E _g) _{Si}$

  3. $(E _g) _{C}\, >\, (E _g) _{Si}\, >\, (E _g) _{Ge}$

  4. $(E _g) _{C}\, =\, (E _g) _{Si}\, =\, (E _g) _{Ge}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
For given elements, the energy band gap of carbon is the maximum and of germanium is the least.
Hence option C is correct.
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

Among the following, the wrong statement in the case of semiconductor is:

  1. Resistivity is in between that of a conductor and insulator.

  2. Temperature coefficient of resistance is negative.

  3. Doping increases conductivity.

  4. At absolute zero temperature, it behaves like a conductor.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For semiconductor, as the temperature coefficient of resistance is negative, at absolute zero temperature, it behaves like an insulator.

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

What is the resistivity of a pure semiconductor at absolute zero ?

  1. Zero

  2. Infinity

  3. Same as that of conductors at room temperature

  4. Same as that of insulators at room temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The electricity conductivity of a semiconductor at $0 K$ is zero. hence resistivity (= 1/electrical conductivity) is infinity.