64
rH - (5.2)
For nondegenerate, spherically symmetric bands, it can be shown that [59] rH 1 1, and that
<,r2>
rH - r2(5)
In general most previous work [5,59] has assumed that equation (5.3) is valid in the case of p-type silicon and thus rH will vary between 1.18 (T(E) - E-1/2 for lattice scattering) and 1.93 (T(E) E3/2 for ionized impurity scattering), if hole-hole scattering is neglected, and will approach unity for the degenerate case. This theory does not allow for values of rH less than one. Experimental evidence indicating values of rH less than one has been attributed to poor quality of the measured samples [5]. Debye and Kohane [63] found that the measured drift mobility for holes is considerably larger than the measured Hall mobility. Values of rH less than unity were also reported by Wolfstirn [15] for the case of gallium-doped silicon. More recent experiments [64] show that a value of rH less than unity is necessary to reconcile differences between the hole concentration measured via Hall coefficient.methods and that inferred from dopant densities determined from C-V and junction breakdown measurements. The usual assumption made is to let rH be equal to one and thus consider the Hall mobility equal to the conductivity mobility. Neglecting the Hall scattering factor alters both the magnitude and temperature dependence of the carrier concentration from that given by the charge balance equation. In fitting data to the charge balance equation, both thermal