Degenerate and non-degenerate semiconductor, Physics

THE SEMICONDUCTOR in which number of electrons or holes is smaller than Nc and Nv density of state in CB or VB are called non-degenerate semiconductor. The general exponential expression for the concentration of electron in the conduction band (CB), is based on replacing Fermi-Dirac statistics with Boltzmann statistics, which is only valid when Ec is several KT above Ef. In other words we assumed that the number of states in the conduction band far exceed the number of electrons there Nc is the measure of the density of states in CB. The Boltzmann expression for n is valid only when n<c. Those semiconductors for which n<cand P<v are termed as Non -degenerate semiconductors. When the semiconductor has been excessively doped with donors, then n may be large typically 1019-1020 cm-3 or greater then Nc . Semiconductor that have n>>Nc or P>>Nv are called Degenerate semiconductor. In this case Pauli Exclusion Principle becomes important in the electron statistics and we use Fermi Dirac statistics. Degenerate semiconductor is used in laser diodes, Zener diodes and ohm contacts in ICs and as metal gates in many microelectronic MOS devices. 

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