Metals, Semiconductors, and Insulators
- For electrons to move within an applied electric field there have to be states available to them.
- A totally filled band cannot contribute to current transport; neither can a totally empty band.
- So, semiconductors at 0 K are perfect insulators.
- With thermal or optical excitation, a number of these electrons can be excited from the valence band to the conduction band, and after that they can contribute to the current transport process.
- At temperatures other than 0 K, the magnitude of the band gap take aparts an insulator from a semiconductor, for example at 300 K, Eg(diamond) = 5 eV (insulator), and Eg (Silicon) = 1.12 eV (semiconductor).
- Number of electrons presented for conduction can be increased greatly in semiconductors via reasonable amount of thermal or optical energy.
- In metals, the bands are either partially filled or they overlap => so, electrons and empty states coexist => great electrical conductivity.