Fig. 6.1 shows the anisotropy function obtained by Monte Carlo simulation. The two branches of the Monte Carlo results stem from the different circumstances in the regions of carrier heating and carrier cooling. Since modeling of the anisotropic temperature is only an approximation of a secondorder effect, usage of a single valued function appears to be justified. An important property is that drops beginning from unity and saturates for high temperatures. This means that the distribution becomes anisotropic at high temperatures whereas the equilibrium distribution stays isotropic, which is consistent with the fact that the equilibrium solution of BOLTZMANN's transport equation is the isotropic MAXWELL distribution function.
Two analytical anisotropy functions shown in Fig. 6.1 have been investigated:

M. Gritsch: Numerical Modeling of SilicononInsulator MOSFETs PDF