Differentiate between conductor and semiconductor in terms of energy band theory.

In terms of energy band theory, conductors and semiconductors can be differentiated as follows:

1. Energy Bands: In conductors, the valence band and conduction band overlap, meaning that electrons can easily move from the valence band to the conduction band. This is why conductors are good at conducting electricity. In semiconductors, the valence band and conduction band are separated by a small energy gap, known as the band gap. This means that some energy is required to move electrons from the valence band to the conduction band.

2. Band Gap: The band gap in conductors is non-existent as the valence and conduction bands overlap. In semiconductors, there is a small band gap. The size of this band gap determines the properties of the semiconductor. If the band gap is small, then less energy is required to move electrons from the valence band to the conduction band, making the material a good semiconductor.

3. Temperature Dependence: The conductivity of conductors decreases with an increase in temperature because the increased thermal energy causes more collisions between electrons and atoms, impeding the flow of electricity. On the other hand, the conductivity of semiconductors increases with an increase in temperature. This is because as temperature increases, more electrons gain enough energy to cross the band gap and move from the valence band to the conduction band, increasing the material's conductivity.

4. Doping: Doping is the process of adding impurity atoms to a semiconductor to increase its conductivity. This is not applicable to conductors as their conduction band is already filled with free electrons.