anisotropy of the energy spectrum is not considered in this model, because from the transport theory for parabolic bands it is known that this anisotropy has no influence on the temperature dependence of mobility, but only on its absolute value [10]. Each of the four scattering mechanisms will now be discussed.
3.3 Acoustical PhononScattering
The relaxation time for scattering by acoustical phonons includes both the possibility of interband as well as intraband scattering. The treatment of the acoustical phonons has been based on the theory of Bir, Normantas, and Pikus [43] where the relaxation times can be expressed in terms of a single constant, Tx, which controls the overall magnitude of the scattering. Both transverse and longitudinal phonons participate in the scattering so that
,3/2
-1 m*l 32 L1 (2) + 3 L ()
acl TX 11 ij 11
C2
2 2 (2) + Yij3 (1)] T 3/21/2
112 + T T (3.7)
and
-1 m2 L (2) + y 3 L2(1) +
Tac2 Tx L22 i 22
c z B21T-(2) + Y 3 T(I T3/2Cu/2 (3.8)
C 2 22ij 22 9