* Energy Bands: In pure semiconductors, the energy levels of electrons are organized into bands. There's a filled valence band (where electrons are normally bound) and an empty conduction band (where electrons can freely move and conduct electricity). There's a gap in energy called the band gap between these two bands.
* The Band Gap: The band gap is the key. For a material to conduct electricity, electrons need to be excited into the conduction band. In pure semiconductors, the band gap is relatively small compared to insulators, but it's still large enough that electrons need a little "push" to jump up.
* Temperature and Conductivity: At very low temperatures, there's not enough thermal energy to excite electrons into the conduction band. Therefore, the pure semiconductor behaves as an insulator. As temperature increases, the thermal energy available increases, and more electrons can jump the band gap, leading to a gradual increase in conductivity.
Why are semiconductors useful?
While they're not as conductive as metals, semiconductors are extremely useful because their conductivity can be controlled through:
* Temperature: As mentioned, increasing temperature increases conductivity.
* Doping: Adding impurities (doping) to the semiconductor can create extra electrons (n-type) or holes (p-type), drastically changing its conductivity.
* Light: Some semiconductors can absorb photons and excite electrons, making them more conductive.
In summary:
Pure semiconductors are not conductors at very low temperatures. They act as insulators due to the band gap. Their conductivity can be manipulated by factors like temperature and doping, making them essential in electronics.
