Energy Band Gap Experiment Viva Question and Answer – Semiconductor 2024

This is the energy gap between the condition and valence bands of a semiconductor (or insulator)

A semiconductor always possess an energy gap between its condition and valence bands. For the conduction of electricity a certain amount of energy is to given to an electron to go from valence band to conduction band. The measure of this energy is called energy gap between two bands. 

There is no band gap as the two bands overlap in their case.

When a p-n junction is reverse biased, then current is due to minority carriers whose concentration is depend on energy gap or band gap.

In a semiconductor, at zero degree Kelvin an electron in valence band does not have sufficient energy to cross the forbidden energy gap so does not reach in conduction band and thus behave as an insulator.

A p-type semiconductor in contact with an n-type semiconductor constitutes a p-n junction.

The range of energy which is possessed by valence electrons is known as valence band. Here the electrons which are situated at outer most orbits are called valence electrons. The valence band consists of valence electrons which are having highest energy.

The range of energies possessed by conducting electrons is known as conduction band. The conduction electrons are responsible for the conduction of current in a conducting material. So, these electrons are called as conduction electrons.

Based on the energy gap the solid materials are classified into 3 types they are : conductors, insulators and semi-conductors.

Semi-conductors are those materials whose electrical conductivity is between conductors and insulators, Insulator are those non-metallic materials which do not have free electrons to conduct current, capable of carrying an electric current.

In conductors, the valence and conduction bands overlap each other. In insulators, there is large energy gap between valence and conduction bands, while in semiconductors this energy gap is not too large so that at room temperature the thermal energy gained by some of the electrons in the valence band is sufficient to make, them jump conductions band, crossing this energy gap.

Those substances which have more and more energy gap between valence and conduction band they are called insulators. In these materials the valence electrons are very lightly bounded to nucleus.

Those substances which have conductivity and resistivity properties in between conductors and insulators are called semiconductor. (ex : Si, Ge) Energy gap of these semiconductors lies between 0.5 to 1.1 ev

German, Selenium, Silicon and Indium.

Free electrons are those electrons that have become dislodge from the outer shell of an atom.

Germanium is a trivalent atom i.e it has four valence electrons in its outer shell which can react with four elements of other atoms. It’s atomic number is 32. The crystal study shows that germanium has crystalline structure and its atom assume the special diamond structure.

Doping is a process of introducing a small amount of an impurity into the germanium crystal.

The conductivity of the crystal depends upon the type and amount of impurity added.

When pentavalent impurity like arsenic or antimony is added to the pure germanium crystal, then the impurity atom donates electrons to the crystal conductivity, therefore it is called donor impurity.

When pentavalent impurity is introduced into the pure germanium crystal four out of the five valence electron of impurity atom i.e arsenic will from covalent bonds with four valence electrons of germanium atom. The remaining fifth electron is free to move about crystal under the action of an electric field these free electrons donated by impurity atoms will move towards the positive terminal of the voltage source.

When trivalent impurity atom is added to germanium crystal, impurity atom that contribute holes are called acceptor because they accepts.