Semiconductors and Semiconductor Devices Physics - Semiconductors and Semiconductor Devices

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

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

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

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

The band gap for silicon is 1.1eV.

1. Find the ratio of the band gap to kT for silicon at room temperature 300K.
2. At what temperature does this ratio become one tenth of the value at 300K?

(Silicon will not retain its structure at these high temperatures.)

In a p-n junction, the depletion region is 400nm wide and an electric field of 5 × 10⁵V/m exists in it.

1. Find the height of the potential barrier.
2. What should be the minimum kinetic energy of a conduction electron which can diffuse from the n-side to the p-side?

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

The potential barrier existing across an unbiased p-n. junction is 0·2 volt. What minimum kinetic energy a hole should have to diffuse from the p-side to the n-side if,

1. The junction is unbiased.
2. The junction is forwardbiased at 0.1 volt.
3. The junction is reverse-biased at 0.1 volt?

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 300K, find the energy of the acceptor levels above the valence band.

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 diffluse from the p-side to the n-side in a p-n junction, the n-side gets positively charged. Explain.

In a transistor:

1. The emitter has the least concentration of impurity.
2. The collector has the least concentration of impurity.
3. The base has the least concentration of impurity.
4. All the three regions have equal concentrations of impurity.

An incomplete sentence about transistors is given below:
The emitter ...... junction is ....... and the collector ..... junction is ..... The appropriate words for the dotted empty positions are, respectively.

1. 'Collector' and 'base'.
2. 'Base' and 'emitter'.
3. 'Collector' and 'emitter'.
4. 'Base' and 'base'.

A semiconductor is doped with a donor impurity:

1. The hole concentration increases.
2. The hole concentration decreases.
3. The electron concentration increases.
4. The electron concentration decreases.

The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of:

1. Phosphorus.
2. Boron.
3. Antimony.
4. Aluminium.

Electric conduction in a semiconductor takes place due to:

1. Electrons only.
2. Holes only.
3. Both electrons and holes.
4. Neither electrons nor holes.

The diffusion current in a p-n junction is:

1. From the n-side to the p-side.
2. From the p-side to the n-side.
3. From the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse-biased.
4. From the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse-biased.

Find the current through the battery circuits shown in figure.

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