The number of free electrons and holes in intrinsic semiconductor increases when the temperature

In a semiconductor it is observed that three-quarters of the current is carried by electrons and one quarters by holes. If the drift speed is three times that of the holes, what is the ratio of electrons to holes?

A

1 : 1

B

1 : 2

C

2 : 1

D

4 : 1

An intrinsic semiconductor has some holes in it at room temperature. What causes these holes?

A

Doping

B

Valence electrons

C

Free electrons

D

Thermal energy

E

None of the above

For an intrinsic semiconductor, $$m_e^ * $$ and $$m_h^ * $$ are respectively, the effective masses of electrons and holes near the corresponding band edges. At a finite temperature, the position of the Fermi level

A

depends on $$m_e^ * $$ but not on $$m_h^ * $$

B

depends on $$m_h^ * $$ but not on $$m_e^ * $$

C

depends on both $$m_e^ * $$ and $$m_h^ * $$

D

depends neither on $$m_e^ * $$ nor on $$m_h^ * $$

A simplified energy band-diagram of an intrinsic semiconductor at thermal equilibrium (300 K) is shown. In the accompanying table, which one of the four cloumns correctly represents the listed parameters? Assume same effective mass for electrons and holes.
Physics of Metals in Metallurgy mcq question image

Physics of Metals in Metallurgy mcq question image

A

Parameter	Energy-difference
Parameter	Column 1	Column 2	Column 3	Column 4
Band-gap	ΔE₂	ΔE₁	ΔE₂	ΔE₁
Electron affinity	$$\frac{{\Delta {E_1}}}{2}$$	ΔE₂ - ΔE₁	$$\frac{{\Delta {E_2}}}{2}$$	ΔE₂ - $$\left( {\frac{{\Delta {E_1}}}{2}} \right)$$
Work function	ΔE₁ + ΔE₂	ΔE₂ - $$\left( {\frac{{\Delta {E_1}}}{2}} \right)$$	ΔE₁ - $$\frac{{\Delta {E_2}}}{2}$$	ΔE₂ + $$\left( {\frac{{\Delta {E_1}}}{2}} \right)$$

Column 1

B

Column 2

C

Column 3

D

Column 4

In an intrinsic semiconductor, the number of free electrons

A

Equals the number of holes

B

Is less than the number of holes

C

Is greater than the number of holes

D

Impossible to say

E

None of the above

At room temperature the number of conducting electrons in an intrinsic semiconductor

A

Is almost equal to the number of valence electrons

B

Is about half the number of valence electrons

C

Is small as compared to the number of valence electrons

D

Is a very small fraction of the number of valence electrons

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

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

A particular intrinsic semiconductor has a resistivity of 50 (ohm-cm) at T = 300 K and 5 (ohm-cm) at T = 330 K. If change in mobility with temperature is neglected, the bandgap energy of the semiconductor is

A

1.9 eV

B

1.3 eV

C

2.6 eV

D

0.64 eV

The probability of electrons to be found in the conduction band of an intrinsic semiconductor at finite temperature is which of the following?

A

Increases exponentially with the increasing bandgap

B

Decreases exponentially with the increasing bandgap

C

Decreases with increasing temperature

D

Is independent of the temperature and the bandgap

An intrinsic silicon sample has 1 million free electrons at room temperature. As the temperature is increased

A

The number of free electrons increases

B

The number of free electrons increases but the number of holes decreases

C

The number of free electrons and holes increase by the same amount

D

The number of free electrons and holes increase but not by the same amount

The number of free electrons and holes in intrinsic semiconductor increases when the temperature

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