Energy Bands Description
A large number of atoms in a crystal stone is closer to each other and more those electrons interact with themselves. The energy level of electrons in their shell is only caused because of the modification in their energy levels. The most important feature of Energy Bands is that the energy states for electrons are continuous in varied ranges. Thus, we can say that the energy level of an atom varies in valence bands and in conduction bands.
Classification of Energy Bands
Gold, Aluminum, Silver, Copper, all these metals allow an electric current to flow through them.
There is no forbidden gap between the valence band and conduction band which results in the overlapping of both the bands. The number of free electrons available at room temperature is large.
Glass and wood are examples of the insulator. These substances do not allow electricity to pass through them. They have high resistivity and very low conductivity.
The energy gap in the insulator is very high up to 7eV. The material cannot conduct because the movement of the electrons from the valence band to the conduction band is not possible.
Germanium and Silicon are the most preferable material whose electrical properties lie in between semiconductors and insulators. The energy band diagram of semiconductor is shown where the conduction band is empty and the valence band is completely filled but the forbidden gap between the two bands is very small that is about 1eV. For Germanium, the forbidden gap is 0.72eV and for Silicon, it is 1.1eV. Thus, semiconductor requires small conductivity.
Energy Band Theory
According to Bohr’s theory, every shell of an atom contains a discrete amount of energy at different levels. Energy band theory explains the interaction of electrons between the outermost shell and the innermost shell. Based on the energy band theory, there are three different energy bands:
- Valence band
- Forbidden energy gap
- Conduction band