Question

Select the correct statement regarding a semiconductor.
1. Acceptor level lies close to the valence bond
2. N-type semiconductor behaves as a conductor at \[0^\circ \] K.
3. All of these
4. Donor level lies close to the valence band

Answer 1

Hint: A semiconductor is a solid whose conductivity is between an insulator and a conductor. The use of semiconductors is for many purposes such as manufacturing transistors, capacitors, integrated circuits, etc.

Complete Step by Step Answer:
Let's understand the conductivity of semiconductors. By introducing impurities to a semiconductor its conductivity can be modified. This process is termed doping. The impurities added are called dopants. The classification of dopants is done in two types, namely, donors and acceptors. When doping a semiconductor is done with donor impurities, the semiconductor formed is n-type. And when the doping of semiconductor is done with acceptor impurities, the semiconductor formed is p-type.

In a semiconductor of n-type, when donor impurities are added, the energy level of the semiconductor becomes high in the semiconductor bandgap. This causes easy excitation of electrons towards the conduction band. In the n-type band structure, the position of the donor level is close to the bottom of the conduction band. Therefore, the 4^th option is wrong.

And the acceptor level lies in proximity to the valence bond. Therefore, option 1 is right.
The conductivity of semiconductors decreases with a decrease in temperature. At a temperature of \[0^\circ \] K, a semiconductor's conductivity decreases and it becomes an insulator. Therefore, option 2 is wrong.
Therefore, option 1 is right.

Note: A semiconductor of p-type is obtained by doping of impurity trivalent atoms like gallium, boron, indium, etc. The impurities when added, cause holes (vacancies of electrons) in the structure. The holes carry the charge and electrons are minority carriers.