Semiconductors and Semiconductor Devices Physics - Semiconductors and Semiconductor Devices

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.

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'.

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.

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?

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

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

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 conμnuously take place?

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?