The simulation area is bounded assuming Neumann
conditions for the electrical and thermal boundary
conditions, setting
= 0
and
= 0.
For HEMTs, which generically are multifinger devices with up to
eight gate fingers in the third dimension, this is a good
assumption for the electrical properties. However, for the
solution of the heat flow equation this approximation introduces
serious errors since the gate to gate finger interaction cannot
be neglected in multifinger devices, as was shown e.g. in [169].
A sound treatment of the thermal boundary
conditions is carried out in Chapter 6.