The results of this calculation are presented in Figures 5.1 and 5.2. These figures show the significant contribution of the mass anisotropy factor to the Hall factor. Since the influence of nonparabolicity is reduced in degenerate material [25], it follows as shown in Figures 5.1 and 5.2, that the variation of rA with temperature is much stronger at low dopant densities, since it is in this dopant density range that the variation of effective mass with temperature is the strongest. We note that the mass anisotropy factor is less than unity for all temperatures considered in this work once the dopant density increases past 6xlO15 cm3. At 300 K, rA is less than unity even for dopant densities as low as 1014 cm-3
5.4 The Scattering Factor
The scattering factor, rS, depicted in Figures 5.3 and 5.4 as a
function of temperature and dopant density, does not follow the traditionally expected variation between 37r/8 = 1.18 and 315ir/512 = 1.93 as the dominant scattering mechanism changes from lattice to ionized impurity scattering. Putley [65] has noted that hole-hole scattering can modify rs" He estimates that for ionized impurity scattering, rS can be reduced from 3157/512 to a value close to unity. At low dopant densities where the dominant scattering mechanism is acoustic phonon scattering, rS varies between 1.08 for T = 100, to 1.24 for T 400 K. The deviation from the traditionally expected value of r S =1.18 is due to the contributions of optical phonon modes at the higher temperatures. Hole-hole collisions also affect the impurity and optical phonon scattering contributions so they become significant even at low temperatures and dopant densities. At higher values of dopant density, the effects of hole-hole scattering on the ionized impurity scattering mechanism