Free Electron and Hole

Free Electron and Hole

1. If a bonded electron absorbs heat energy from the surrounding, it may be promoted to higher energy level.
2. These electrons are free to move when they are at a higher energy level.
3. If an electron is promoted to higher level, a vacancy is left in the valence shell, and it is called a hole.
4. A hole has the tendency to pull electrons. Therefore a hole is assumed carries positive charge.
5. Both of the free electrons and the holes can help to conduct electric current.
6. Therefore, with the presence of the free electrons and holes, the conductivity of a semiconductor is higher than an insulator.

Resistance Change Due to Temperature Change

1. As the temperature increases, more and more electrons are getting promoted to become free electrons and at the same time creating more and more holes. Therefore the conductivity of a semiconductor increases as the temperature increases.
2. The graph below shows the resistivity change of a conductor and semiconductor against the temperature. The resistance of a semiconductor decreases as the temperature increases.