What is a semiconductor? Describe the two main types of semiconductor and contrast their conduction mechanism.

Explanation

Those solids which have intermediate conductivites ranging from `10^(-6)` to `10^(4) ohm^(-1)m^(-1)` are classified as semiconductors. As the temperature rises, there is a rise in conductivyt value because electrons from the valence band jump to conduction band.
(i) n-type semiconductor: When a silicon or germanium crstal is doped with group 15 element like P or As, the dopant forms four covalent bonds like Si or Ge atom but the fifth electron, not used in bonding. becomes delocalised and continues its share towards electrical conducrtion Thus silicon or germanium doped with P or As is called H-type semiconducot a -indicative of negative since it is the electron that conducts electricity.
(ii) p-type semiconductor: When a silicon or germanium is doped with group 13 element like B or Al, the dopand is present only with three valence electrons. An electron vacancy or a hole is created at the place of missing fourth electron Here, this hole moves throughout the crystal like a posiive charge giving rise to electrical conducitivyt. thus Si or Ge doped with B or Al is called p-type semiconductor P stands for positive hole, since it is the position hole that is responsible for conduction.