Monte Carlo Calculation of Hole Transport in Bulk Zincblende Phase of GaN including a Pseudopotential Calculated Band St
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Figure 1. (a) Band structure of zincblende type GaN . (b) Band structure of wurtzite type GaN. Both are calculated using an empirical pseudopotential method. 479 Mat. Res. Soc. Symp. Proc. Vol. 395 ©1996 Materials Research Society
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difference is especially noticeable when one considers the valence bands. In addition to the fact that the number of valence bands within the energy range of interest for transport studies is higher in the wurtzite phase vs. the zincblende phase, extreme band warping creates a non-trivial problem to be solved while modeling the wurtzite type GaN. Although there are several theoretical investigations made to date, to determine the electronic transport properties of bulk GaN [6-9], similar studies are yet to be performed for holes in either possible phase. In addition to complementing the steady-state information already obtained for the electrons [10] such as the drift velocity, average particle energy, etc., it is important to determine the high-energy behavior of holes in GaN. Knowledge of very high energy transport, i.e., the calculation of the impact ionization rates, is particularly useful in assessing the performance of possible ultraviolet avalanche photodetectors. It is the purpose of this paper to present the first theoretical calculations of the steady-state hole transport properties in the zincblende phase of GaN. Here, it should be noted that the numerous intersections of the valence bands in wurtzite type GaN presents some added complexity in calculating its transport properties. The pseudopotential method labels the bands with respect to their ascending order in energy at each k-point, regardless of the bands' apparent continuity. From a transport viewpoint, this can cause a discrepancy during the free flight of a particle since a particle can be subjected to an abrupt momentum change without the interference of a scattering agent. Even though it is possible to proceed with an improved ordering of the bands beyond what was given by the original pseudopotential calculation, it is a very difficult task to make the new ordering consistent throughout the entire First Brillouin zone of the wurtzite structure. For this reason, we delay the examination of hole transport in wurtzite GaN to a later work where a comparison can then be made between the transport properties of wurtzite and zincblende phases of GaN. The present calculations are carried out using an ensemble Monte Carlo simulator that includes the full details of the valence bands within the energy range of interest. Results obtained for the steady-state drift velocity, average hole energy and band occupancy under electric field magnitudes up to 1000 kV/cm are presented. In Section II, the details of the Monte Carlo model are described. The simulation results are given and discussed in Section III and conclusions are drawn in Section IV. MODEL DESCRIPTION The calculations are performed using an ensemble Monte Carlo simulator which includes the top three ban
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