Steady-state and transient electron transport in bulk GaN employing an analytic bandstructure

We have studied the steady-state and transient electron transport in bulk gallium nitride using an ensemble two valley Monte-Carlo approach. We employ an analytic form for the bandstructure which is non-parabolic and includes the inflection point predicted by empirical pseudopotential methods. It has been suggested that the inflection point could give rise to a negative effective mass which would, in turn, give rise to a negative-differential conductivity (NDC). We examine the character of the NDC by varying the energy separation to the upper valleys. We find that for steady-state velocity field characteristics, the transferred electron effect dominates over the negative mass effect. However, the transient characteristics show a small temporary dominance of the negative mass effect when the valley separation is 1.9 eV.