Module 6 : PHYSICS OF SEMICONDUCTOR DEVICES
Lecture 34 : Intrinsic Semiconductors
Gallium belongs to Group III and bonds with arsenic which belongs to Group V to give a III-V semiconductor. In GaAs, the bonding is partly covalent and partly ionic. Other commonly known III-V semiconductors are GaN, GaP, InSb etc. Like the III-V compounds, Group II elements combine with Group VI elements to give semiconductors like CdTe, CdS, ZnS etc. Several industrially useful semiconductors are alloys such as Al $ _x$GA $ _{1-x}$As.
  The number of carriers in a band at finite temperatures is given by $ \int n(E)f(E)dE $, where $ n(E)$ is the density of state and $ f(E)$ is the Fermi function which gives the thermal probability. If $ E-E_F\gg kT$, we may ignore the term 1 in the denominator of the Fermi function and approximate it as
 
$\displaystyle f_e(E) \simeq e^{(E-E_F)/kT}$
 
3
5
10
19
21