An oscillator is an electronic device which generates AC voltage froID DC power. It is basically a positive feedback amplifier with infinite voltage gain.
Types of Semiconductor
( i) Intrinsic Semiconductor A semiconductor in its pure state is called intrinsic semiconductor.
( ii) Extrinsic Semiconductor A semiconductor doped with suitable impurity to increase its impurity, is called extrinsic semiconductor.
On the basis of doped impurity extrinsic semiconductors are of two types
( i) n-type Semiconductor Extrinsic semiconductor doped with pentavalent impurity like As, Sb, Bi, etc in which negatively charged electrons works as charge carrier, is called n-type semiconductor.
Every pentavalent impurity atom donate one electron in the crystal, therefore it is called a doner atom
( ii) p-type Semiconductor Extrinsic semiconductor doped with trivalent impurity like Al, B, etc, in which positively charged holes works as charge carriers, is called p-type semiconductor.
Every trivalent impurity atom have a tendency to accept one electron, therefore it is called an acceptor atom.
In a doped semiconductor n e n h = n 2 i where n e and n h are the number density of electrons and holes and n i is number density of intrinsic carriers, i. e., electrons or holes.
In n-type semiconductor, n e > > n h In p-type semiconductor, n h > > n e
Electrical conductivity of extrinsic semiconductor is given by σ = 1 / ρ = e( n e μ e + n h μ h) where ρ is resistivity, μ e and μ h are mobility of electrons and holes respectively. Note Energy gap for Ge is 0.72 eV and for Si it is 1.1 eV.