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 .