carrier concentration and dopant impurity activation energy are overestimated by the assumption of unity Hall factor. A more complete theoretical treatment of the Hall factor can be undertaken by considering the nonparabolic and anisotropic nature of the valence band of silicon.
Chapter II described the constant energy surfaces as warped spheres. Warping of the energy surfaces has a significant effect on the ratio of Hall to conductivity mobility. When the bands are warped, the Hall factor depends on the degree of warping as well as the scattering mechanism [30].
The Hall mobility is the product of the ohmic conductivity and the Hall coefficient
H= C CRH (5.4)
In the low field limit the Hall coefficient for a nonparabolic, anisotropic band i is given by [37]
RHi Hi2 (5.5)
CCi
Thus by substituting equations (2.9) and (2.10) into equation.(5.5) the Hall coefficient can be expressed as
R rHi (5.6)
Hi pie
where