Intrinsic Semiconductor

Q.

Fermi energy level for intrinsic semiconductors lies

Q.

Find the maximum wavelength of electromagnetic radiation which can create a hole-electron pair in germanium. the band gap in germanium is 0.65 eV.

Q.

The mobility of electrons in a semiconductor is defined as the ratio of their drift velocity to the applied electric field. If, for an n-type semiconductor, the density of electrons is ${10}^{19}{m}^{-3}$ and their mobility is $1.6m^{2}Vs$ then the resistivity of the semiconductor (since it is an n-type semiconductor contribution of holes is ignored) is close to

Q. a straight wire of linear charge density λ= 3μ C/m and area of cross section a=4mm^2 is given as shown in figure. When wire is pulled with the speed 2m/s hen the curreng associated with it is

Q.

By increasing the temperature, the specific resistance of a conductor and a semiconductor

1. increases for both

2. decreases for both

3. increases, decreases

4. decreases, increases

Q.

When the conductivity of a semiconductor is only due to the breaking of covalent bonds, the semiconductor is called

1. $\mathrm{n}-\mathrm{type}$

2. $\mathrm{p}-\mathrm{type}$

3. intrinsic

4. extrinsic

Q.

In an n-type semiconductor, the donor energy level lies

1. At the center of the energy gap

2. Just below the conduction band

3. Just above the valence band

4. In the conduction band

Q.

The conductivity of an intrinsic semiconductor depends on temperature as $\sigma ={\sigma }_0{e}^{-\Delta E/2KT},$ where ${\sigma }_0$ is a constant. Find the temperature at which the conductivity of an intrinsic germanium semiconductor will be double of its value at T = 300 K. Assume that the gap for germanium is 0.650 eV and remains constant as the temperature is increased.

Q.

What property of an element is measured by electronegativity?

Q.

Germanium is an example of?

1. Insulator

2. n-type semiconductor

3. p-type semiconductor

4. Intrinsic semiconductor

Q. Two materials $\text{Si}$ and $\text{Cu}$, are cooled from $300\text{K}$ to $60\text{K}$. What will be the effect on their resistivity ?

​​​​​​​$[$1 Mark$]$

1. Resistivity of both $\text{Si}$ and $\text{Cu}$ increases
2. Resistivity of $\text{Si}$ increases and resistivity of $\text{Cu}$ decreases
3. Resistivity of both $\text{Si}$ and $\text{Cu}$ decreases
4. Resistivity of $\text{Si}$ decreases and resistivity of $\text{Cu}$ increases

Q. A hole behaves like it has a charge.

1. negative
2. positive
3. zero

Q.

On increasing the number of electrons striking the anode of an X-ray tube, which one of the following parameters of the resulting X-rays would increase:-

1. penetration power

2. frequency

3. wavelength

4. intensity

Q. Resistance of which of the following solids decreases on increasing temperature? (Consider no change in dimensions)

1. Metals
2. Semiconductors only
3. Insulators only
4. Insulator and semiconductors

Q.

The product of the hole concentration and the conduction electron concentration turns out to be independent of the amount of any impurity doped. The concentration of conduction electrons in germanium is $6\times {10}^{19}$ per cubic metre. When some phosphorus impurity is doped into a germanium sample, the concentration of conduction electrons increases to $2\times {10}^{23}$ per cubic metre. Find the concentration of the holes in the doped germanium.

Q. Suppose a pure Si crystal has $5\times {10}^{28}{\text{atom m}}^{–3}$. It is doped with $1\text{ppm}$ concentration of pentavalent Arsenic. Calculate the number of holes $(n_i=2.5\times {10}^{16}{\text{m}}^{–3})$.

1. $8\times {10}^9{\text{m}}^{-3}$
   
2. $1.25\times {10}^{10}{\text{m}}^{-3}$
3. $6.25\times {10}^{22}{\text{m}}^{-3}$
4. $4.5\times {10}^{22}{\text{m}}^{-3}$

Q.

Estimate the proportion of boron impurity which will increase the conductivity of a pure silicon sample by a factor of 100. Assume that each boron atom creates a hole and the concentration of holes in pure silicon at the same temperature is $7\times {10}^{15}$ holes per cubic metre. Density of silicon is $5\times {10}^{28}$ atoms per cubic metre.

Q.

In a semiconductor mobility of electron, i.e. drift velocity per unit applied electric field is $1.6m^2/Vs$. Density of electrons is ${10}^{19}/m^3$. (Neglect holes concentration). Resistivity of semiconductor is:

1. $0.4\Omega m$

2. $2\Omega m$

3. $4\Omega m$

4. $0.2\Omega m$

Q.

Is Silver Used in Semiconductors?

Q. In a region of space, the electric field is given by $\overrightarrow{E}=8\hat{i}+4\hat{j}+3\hat{k}$. The electric flux through a surface of area $100$ units in the xy plane is :

1. $800$ units
2. $300$ units
3. $400$ units
4. $1500$ units

Q. The solids which have the negative temperature coefficient of resistance are:

1. Semiconductors only
2. Insulators and semiconductors
3. Metals
4. Insulators only

Q.

Choose the correct alternative:

(a) Alloys of metals usually have (greater/less) resistivity than that of their constituent metals.

(b) Alloys usually have much (lower/higher) temperature coefficients of resistance than pure metals.

(c) The resistivity of the alloy manganin is nearly independent of/increases rapidly with increase of temperature.

(d) The resistivity of a typical insulator (e.g., amber) is greater than that of a metal by a factor of the order of (10²²/10³).

Q. To which band does the Fermi level belong - valence band or conduction band?

Q.

Is mercury a semiconductor?

Q. what is the dimension for permitivity of free space?

Q. Assertion :A pure semiconductor has negative temperature coefficient of resistance. Reason: In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases.

1. Assertion is true, Reason is true; Reason is a correct explanation for Assertion
2. Assertion is true, Reason is true; Reason is not a correct explanation for Assertion
3. Assertion is true, Reason is false
4. Assertion is false, Reason is true

Q.

When the electrical conductivity of a semi- conductor is due to the breaking of its covalent bonds, then the semiconductor is said to be

1. Donar
2. Acceptor
3. Intrinsic
4. Extrinsic

Q. Match List-1 with List-2

List-1	List-2
A. Intrinsic semiconductor	E. Donor level
B. N-type semiconductor	F. Acceptor level
C. p-type semiconductor	G. Immobile ions
D. Depletion layer	H. Fermi energy levels is at the centre of forbidden energy gap I. Fermi energy level is near the conduction band

1. A-F B-E, G C-H D-I
2. A-E B-F C-G D-H, I
3. A-I B-H C-G D-E, F
4. A-H B-E, I C-F D-G

Q. Consider the following two statements

$\left(a\right)$ Resistance of a semiconductor decreases with increase in temperature.

$\left(b\right)$ Resistance of a conductor decreases with increase in temperature.

The correct statement(s) is/are

1. Only $\left(b\right)$
2. Neither $\left(a\right)$ nor $\left(b\right)$
3. Only $\left(a\right)$
4. Both $\left(a\right)$ and $\left(b\right)$

Q. With rise in temperature the electrical conductivity of intrinsic semiconductor:

1. increases
2. decreases
3. first increases and then decreases
4. first decreases and then increases