CHAPTER IV
HOLE DENSITY AND RESISTIVITY
4.1 Introduction
The resistivity of semiconductor materials is one of their most useful and easily measured properties. Theoretical calculations of resistivity depend on the formulation of conductivity mobility, and the determination of hole density. For extrinsic semiconductors, the hole density is determined primarily by the percentage of ionization of impurity atoms. The following sections discuss the dependence of hole density and resistivity on temperature and dopant density.
4.2 Ionization of.Impurity Atoms
For the case of Fermi-Dirac statistics, the hole density is given
by
2k Tm* 3/2
p = h2 0 F1(n) (4.1)
where, m*, the density-of-states effective mass, contains information pertaining to the nonparabolic nature of the valence band. In the limit of low dopant densities, equation (4.1) reduces to
p = Nvexp(n) (4.2)
where N 2(2 Tr m* k T/h2)3/2 is the effective density o'f valence band
whr V D( 0 k
states. For the range of temperatures considered in this study, the
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