Extrinsic Semiconductor
A semiconductor whose electrical conductivity is dominated by intentional impurity dopants rather than thermal excitation across the band gap.
Governing formula
n p = n_i² (Mass Action Law)
SI unit
cm⁻³ (Dopant Carrier Density)
In depth
Extrinsic semiconductors are classified as either n-type or p-type depending on whether free electrons or holes predominate. Dopants introduce localized energy levels inside the band gap close to the conduction or valence band edges.
Examples in the real world
Silicon doped with boron or arsenic used to fabricate transistors, diodes, and microprocessors.