Module 8 : Laser- II
Lecture   : Various types of Lasers
  Likewise, the Fermi level of a p-type degenerate semiconductor is pushed into the valence band and lies at the bottom of the acceptor band. The distribution function (at $ T>0$) and the density of states are shown along with the schematic band diagram.
\includegraphics{laser20b.eps}
 

Consider a p-type degenerate semiconductor. $ f(E)$is the probability that a state of energy $ E$is occupied by an electron. It follows that $ 1-f(E)$is the probability that a state of energy $ E$is occupied by a hole. Recalling that
$\displaystyle f(E) = \frac{1}{1+e^{(E-E_F)/kT}}$

if $ E\gg E_F$, the denominator is large. $ f(E)$is, therefore, small. Thus, if the Fermilevel is inside the valence band, for $ E>E_F$, the probability of holes can be large. Likewise, for an type degenerate semiconductor, the probability of occupation of electrons in the conduction band can be large.

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