Energy Band Formation and Energy Band Diagram

In electrical or electronics engineering semiconductor physics is an important part because you have to know how electrons take part in conduction. Electrical engineering or electronics engineering mainly deals with the flow of current. In this article you'll get a brief idea about the energy band, also how electrons cross the band gap to takes part in conduction.

In chemical bond formation outermost electrons will form a part of the bond. When two atoms come closer then there will be forces acting between them-attractive force & repulsive force. 

By electrostatics, in the presence of electrostatic force potential energy changes. So, when the bond will be formed then the energy level of electrons will change & at each energy level there will be some electron.

This energy level splits up to two energy levels-

     1. Bonding molecular orbital

     2. Anti-bonding molecular orbital

At bonding molecular orbital, energy is low so more number of electrons will present here as it is the most stable region & at anti-bonding molecular orbital energy is high so a few number of electrons will present as it is the less stable region.

When many such energy levels will appear because many such atoms are combining together out of those some will be bonding & some anti-bonding. When these energy levels are very close together then they will form a band.

Types of band -  a. valance band
                          b. conduction band

In valance band electrons are attached with atoms but in conduction band electrons take part in conduction.

• Energy or Band gap - Energy required to send an electron from valance to conduction band is called as energy or band gap.

           It's unit is electron-volt(eV)

           So, band gap = (Ec-Ev)

         where Ec is the minimum energy of the conduction band & Ev is the maximum energy of                   the valance band.

• Fermi energy - It is the highest energy occupied by electrons in a body at 0K temperature.

At T=0K, thermal energy KT/e=0, so the electrons in the valance band will not get sufficient energy to reach the conduction band. As the conduction band is empty so there will be no current flow.

Now, if valance band electrons will get sufficient energy to escape the force of the nucleus then they will start to conduct current as they will lie in the conduction band.