Question

Why does pure silicon, which is an insulator, behave as a semiconductor on heating?

Answer 1

In pure silicon, electrons are present in the valence band. The conduction band is empty. The electrons in the valence band are not free to move. But the electrons in the conduction band are free to move. When pure silicon is heated, few electrons are excited. They leave valence band and enter conduction band. The electrons in the conduction band can conduct electricity. Hence, pure silicon, which is an insulator, behave as a semiconductor on heating.