What is a semiconductor? What aren-type and p-type semiconductors?

Explanation

The solids which exhibits intermediate conductivities ranging from `10^(-6)` to `10^(-4) Omega^(-1)m^(-1)` are known as semiconductors .In this case , the gap between the valence band and conduction band is small. Therefore some of the electrons may jump from valence band to conduction band and some conductivity is observed Pure substances like silicon and germanium exhibit conducting behaviour and are called intrinsic semiconductors .On the basis of impurities added for doping ,semiconductors are of two types .
(a) n-type Semiconductor When a silicon or germanium like P or As , the dopant atoms with five valence electrons occupy some of the lattice sites normally occupied by silicon atom .
The dopant atom uses four of its electrons for covalent bonding but the fifth extra electron becomes delocalised and this extra electron increases the conductivity of Si crystal .
Hence silicon doped with electron rich impurity is called n-tye semiconductor .

(b)p - type Semiconductor When a silicon or germanium crystal is doped with group 13 elements like B , l or Ga which contains only three valence electrons , the dopant atoms occupy some of the lattice sites normally occupied by silicon atoms .
The place where the fourth valence electron is missing is called electron hole or electron vacancy .These holes can move through the crystal like a positive charge and increase the conductivity of Si crystal .
Hence ,silicon doped with electron deficient impurity is called p - type semiconductor .