Question

Draw separate energy band diagrams for conductors, semi-conductors and insulators and label each of them.

Answer 1

Hint: Understanding about the valence band, conduction band and forbidden band will help to draw the energy band diagram of each material. Conductors don’t have forbidden band gaps. Insulators have large band gaps. Semiconductors possess small band gaps.

Complete step-by-step answer:
An energy band is the range of energy of electrons possessed in an atom. According to the energy band theory, the valence band, conduction band and forbidden band determine the conductive properties of materials. Valance band can be defined as the last filled energy band of material at 0K. Valence bands never get empty. The electrons in the valence band are unable to obtain energy from any external sources of the electric field. A conduction band can be defined as the first unfilled energy band at 0K. Here, the density of the electrons is very low. The electrons in this band can gain energy from the external fields. The forbidden band is also known as the energy bandgap. Since this is the difference in energy levels of conduction and valence band. In this band, no electrons will occupy. Electrons needed energy for the jumping from the valence to the conduction band.

Insulator;

This material has a large bandgap. Due to large bandgap, the electrons from the valence band can’t move into the conduction band. Hence the valence band remains to fill and the conduction band remains empty. Diamond glass is the example for insulators.

Conductor;

This material has typically zero energy bandgap. Valence electrons can easily move to the conduction band. This overlapping band diagram shows the availability of a large number of charge carriers. Metals are in the category of the conductor.

Semiconductor;

In these materials, conduction and valence bands are separated by a small energy gap. So these materials required some energy for the conduction. Then only the electrons from the valence band can jump into the conduction band. The semiconductors will behave like an insulator at 0 K. At this time no electrons are not available in the conduction band. Valence electrons will acquire more energy and thus more electrons can participate in the conduction if we are applying more temperature. When an electron jumps to the conduction band, then it will create a vacancy in the conduction band. This vacancy is known as a hole. So we can simply say one thermally energized electron can make a pair of an electron and a hole. Commonly used semiconductor materials are silicon and germanium.

Note: It is easy to understand the material conductivity behaviour with the help of energy band diagrams. It’s very hard to say the maximum bandgap of semiconductor material. If the bandgap is less than 2eV, then it is known as conventional semiconductors. If the bandgap is larger than 2eV, then the semiconductor materials known as wide bandgap semiconductor. These will show the intermediate properties between conventional semiconductors and wide bandgap semiconductors.