Materials are classified by by the energy gap between the material’s valence band and the conduction band. The valence band is the band consisting of the valence electron, and the conduction band remains empty.
The gap between these two bands is called forbidden energy gap and conduction takes place when an electron jumps from valence band to conduction band. The wider the gap, the higher the energy it requires for an electron to jump from valence band to the conduction band
Types of Materials
Conductor: The electron requires minimum energy to jump from valence ban as the energy gap is absent or conduction band, and valence band overlaps each other.
Insulator: The electron requires a significant amount of energy to shift an electron from valence to conduction band, as this gap is vast. Insulators are poor conductors of electricity.
Semiconductors: These have an energy gap which is in between that of conductors and insulators.The materials are neither conductor nor insulator with energy gap of about 1 eV (electron volt).
Types of Semiconductors
Intrinsic semiconductor.semiconductor in its pure form is called as In pure semiconductor number of electrons (n) is equal to number of holes
Extrinsic semiconductors are impure semiconductors Extrinsic semiconductor is formed by doping with a small amount of impurity.
N Type Semiconductor: An N type semiconductor is formed by adding pentavalent (five valence electrons) impurity in pure semiconductor crystal, The majority carriers are electrons and minority carriers are holes.
P Type Semiconductor: A p-type semiconductor is formed by adding trivalent ( three valence electrons) impurity in a pure semiconductor. The majority carriers are holes, and minority carriers are electrons.
PN Junction Theory
A PN junction is formed by combining a P-Type Material and an N-Type Material forming a semiconductor diode.