Consider the following statements: The main contribution to photoconduction is by 1. the generation of electron and hole pair by a photon 2. a donor electron jumping into the conduction band because of a photon’s energy 3. a valence electron jumping into an acceptor state because of a photon’s energy Which of the above statements is/are correct?

Which of the following statements is/are correct? 1) Conductor contains a large number of electrons in the conduction band at room temperature. No energy gaps exist and the valence and conduction bands overlap. 2) A semiconductor is a material in which the energy gap is so large that practically no electron can be given enough energy to jump this gap. 3) An insulator is a solid with an energy gap small enough for electrons to cross rather easily from the valence band to conduction band.

A

1 only

B

2 only

C

3 only

D

1, 2 and 3

The process of excitation of an electron from valence band to conduction band leaves an empty hole in the valence band and is called as ____________

A

Detection

B

Absorption

C

Degeneration of an electron-hole pair

D

Regeneration of an electron-hole pair

An intrinsic semiconductor with mass of a hole m_h, and mass of an electron m_e is at a finite temperature T. If the top of the valence band energy is E_v and the bottom of the conduction band energy is E_c, the Fermi energy of the semiconductor is

A

$${E_F} = \left( {\frac{{{E_v} + {E_c}}}{2}} \right) - \frac{3}{4}{k_B}T\ln \left( {\frac{{{m_h}}}{{{m_e}}}} \right)$$

B

$${E_F} = \left( {\frac{{{k_B}T}}{2}} \right) + \frac{3}{4}\left( {{E_v} + {E_c}} \right)\ln \left( {\frac{{{m_h}}}{{{m_e}}}} \right)$$

C

$${E_F} = \left( {\frac{{{E_v} + {E_c}}}{2}} \right) + \frac{3}{4}{k_B}T\ln \left( {\frac{{{m_h}}}{{{m_e}}}} \right)$$

D

$${E_F} = \left( {\frac{{{k_B}T}}{2}} \right) - \frac{3}{4}\left( {{E_v} + {E_c}} \right)\ln \left( {\frac{{{m_h}}}{{{m_e}}}} \right)$$

Is the following statement true? Statement: On the basis of band theory of solids the semi-conductors have a completely filled valence band, a partially filled conduction band and a narrow forbidden band.

A

Statement is false

B

Statement is true

The current due to electron flow in conduction band is the hole current in valence band.

A

Equal to

B

Less than

C

Greater than

D

Any of the above

At what condition, the rate of electron capture from the conduction band and the rate of the electron emission back into the conduction band must be equal?

A

Thermal equilibrium

B

At room temperature

C

T=250K

D

At boiling temperature

Which of the following equations represent the correct expression for the band diagram of the p-n junction? (E1=difference between the fermi level of material and conduction band of n material and E2=difference between the conduction band of n material and fermi level of n material)

A

Ecn – E f = (1/2)*EG – E1

B

Ecn – E f = (1/2)*EG – E2

C

Ef – Ecp = (1/2)*EG – E1

D

Ecn – Ef = (1/2)*EG + E1

The important parameter for exciting an electron with energy required from valence band to conduction band is?

A

Wavelength

B

Absorption coefficient

C

Responsivity

D

Band gap energy

Which of the following statements are correct? 1. The pair (AB) is controllable implies that the pair (ATBT) is observable. 2. The pair (AB) is controllable implies that the pair (ATBT) is unobservable. 3. The pair (AC) is observable implies that the pair (ATCT) is controllable. 4. The pair (AC) is observable implies that the pair (ATCT) is uncontrollable. where: A, B and C are having their standard meanings

A

1 and 3 only

B

1 and 4 only

C

2 and 3 only

D

2 and 4 only

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

A

B

C

D

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