HC Verma solutions for Concepts of Physics Vol. 2 [English] Class 11 and 12 chapter 23 - Semiconductors and Semiconductor Devices [Latest edition]

How many 1s energy states are present in one mole of sodium vapour? Are they all filled in normal conditions? How many 3s energy states are present in one mole of sodium vapour? Are they all filled in normal conditions?

There are energy bands in a solid. Do we have really continuous energy variation in a band ro do we have very closely spaced but still discrete energy levels?

The conduction band of a solid is partially filled at 0 K. Will it be a conductor, a semiconductor or an insulator?

In semiconductors, thermal collisions are responsible for taking a valence electron to the conduction band. Why does the number of conduction electrons not go on increasing with time as thermal collisions continuously take place?

When an electron goes from the valence band to the conduction band in silicon, its energy is increased by 1.1 eV. The average energy exchanged in a thermal collision is of the order of kT which is only 0.026 eV at room temperature. How is a thermal collision able to take some to the electrons from the valence band to the conduction band?

What is the resistance of an intrinsic semiconductor at 0 K?

We have valence electrons and conduction electrons in a semiconductor. Do we also have 'valence holes' and 'conduction holes'?

When a p-type impurity is doped in a semiconductor, a large number of holes are created, This does not make the semiconductor charged. But when holes diffuse from the p-side to the n-side in a p-n junction, the n-side gets positively charged. Explain.

The drift current in a reverse-biased p-n junction is increased in magnitude if the temperature of the junction is increased. Explain this on the basis of creation of hole-electron pairs.

An ideal diode should pass a current freely in one direction and should stop it completely in the opposite direction. Which is closer to ideal-vacuum diode or a p-njunction diode?

Consider an amplifier circuit using a transistor. The output power is several times greater than the input power. Where does the extra power come from?

Calculate the number of states per cubic metre of sodium in 3s band. The density of sodium is 1013 kgm⁻³. How many of them are empty?

In a pure semiconductor, the number of conduction election 6 × 10¹⁹ per cubic metre. How many holes are there in a sample of size 1 cm × 1 mm?

Indium antimonide has a band gap of 0.23 eV between the valence and the conduction band. Find the temperature at which kT equals the band gap.

The band gap for silicon is 1.1 eV. (a) Find the ratio of the band gap to kT for silicon at room temperature 300 K. (b) At what temperature does this ratio become one tents of the value at 300 K? (Silicon will not retain its structure at these high temperatures.)

(Use Planck constant h = 4.14 × 10^-15 eV-s, Boltzmann constant k = 8·62 × 10^-5 eV/K.)

When a semiconducting material is doped with an impurity, new acceptor levels are created. In a particular thermal collision, a valence electron receives an energy equal to 2kT and just reaches one of the acceptor levels. Assuming that the energy of the electron was at the top edge of the valence band and that the temperature T is equal to 300 K, find the energy of the acceptor levels above the valence band.

The band gap between the valence and the conduction bands in zinc oxide (ZnO) is 3.2 eV. Suppose an electron in the conduction band combines with a hole in the valence band and the excess energy is released in the form of electromagnetic radiation. Find the maximum wavelength that can be emitted in this process.

Suppose the energy liberated in the recombination of a hole-electron pair is converted into electromagnetic radiation. If the maximum wavelength emitted is 820 nm, what is the band gap?

(Use Planck constant h = 4.14 × 10^-15 eV-s, Boltzmann constant k = 8·62 × 10^-5 eV/K.)

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.

(Use Planck constant h = 4.14 × 10^-15 eV-s, Boltzmann constant k = 8·62 × 10^-5 eV/K.)

In a photo diode, the conductive increases when the material is exposed to light. It is found that the conductivity changes only if the wavelength is less than 620 nm. What is the band gap?

(Use Planck constant h = 4.14 × 10^-15 eV-s, Boltzmann constant k = 8·62 × 10^-5 eV/K.)

Let ΔE denote the energy gap between the valence band and the conduction band. The population of conduction electrons (and of the holes) is roughly proportional to e^−ΔE/2kT. Find the ratio of the concentration of conduction electrons in diamond to the in silicon at room temperature 300 K. ΔE for silicon is 1.1 eV and for diamond is 6.1 eV. How many conduction electrons are likely to be in one cubic metre of diamond?

The conductivity of a pure semiconductor is roughly proportional to T^3/2 e^−ΔE/2kT where ΔE is the band gap. The band gap for germanium is 0.74 eV at 4 K and 0.67 eV at 300 K. By what factor does the conductivity of pure germanium increase as the temperature is raised from 4 K to 300 K?

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 × 10¹⁵ holes per cubic metre. Density of silicon 5 × 10²⁸ atoms per cubic metre.

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 × 10¹⁹ per cubic metref conduction electrons increases to 2 × 10²³ per cubic metre. Find the concentration of the holes in the doped germanium.. When some phosphorus impurity is doped into a germanium sample, the concentration o

The conductivity of an intrinsic semiconductor depends on temperature as σ = σ₀e^−ΔE/2kT, where σ₀ 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.

(Use Planck constant h = 4.14 × 10^-15 eV-s, Boltzmann constant k = 8·62 × 10^-5 eV/K.)

A semiconducting material has a band gap of 1 eV. Acceptor impurities are doped into it which create acceptor levels 1 meV above the valence band. Assume that the transition from one energy level to the other is almost forbidden if kT is less than 1/50 of the energy gap. Also if kT is more than twice the gap, the upper levels have maximum population. The temperature of the semiconductor is increased from 0 K. The concentration of the holes increases with temperature and after a certain temperature it becomes approximately constant. As the temperature is further increased, the hole concentration again starts increasing at a certain temperature. Find the order of the temperature range in which the hole concentration remains approximately constant.

(Use Planck constant h = 4.14 × 10^-15 eV-s, Boltzmann constant k = 8·62 × 10^-5 eV/K.)

In a p.n junction, the depletion region is 400 nm wide and an electric field of 5 × 10⁵ V m⁻¹ exists in it. (a) Find the height of the potential barrier. (b) What should be the minimum kinetic energy of a conduction electron which can diffuse from the n-side to the p-side?

In a p-n junction, a potential barrier of 250 meV exists across the junction. A hole with a kinetic energy of 300 meV approaches the junction. Find the kinetic energy of the hole when it crosses the junction if the hole approached the junction (a) from the p-side and (b) from the n-side.

The drift current in a p-n junction is 20.0 µA. Estimate the number of electrons crossing a cross section per second in the depletion region.

When the base current in a transistor is changed from 30µA to 80µA, the collector current is changed from 1.0 mA to 3.5 mA. Find the current gain β.

A load resistor of 2kΩ is connected in the collector branch of an amplifier circuit using a transistor in common-emitter mode. The current gain β = 50. The input resistance of the transistor is 0.50 kΩ. If the input current is changed by 50µA. (a) by what amount does the output voltage change, (b) by what amount does the input voltage change and (c) what is the power gain?