4.4.4 Energy Relaxation Times
The energy relaxation times are used in the HD mobility models, in the
energy balance equations of the hydrodynamic transport model, and in
the lattice heat flow equation. They can be either set constant or
calculated using the following model depending on the carrier energy:

(4.81) 
For GaN and InN we use the parameter sets as listed
in Table 4.12, while for AlN a constant relaxation time of
ps is assumed. Special care is taken that the
relaxation times never reach negative values even at high electric
fields (for which Si models indeed yield negative erroneous results).
Table 4.12:
Parameters for the energy relaxation time model [ps].




GaN 
0.21 
0.004 
0.0 
InN 
0.21 
0.012 
0.0 
S. Vitanov: Simulation of High Electron Mobility Transistors