THEORY OF HOLE INITIATED IMPACT IONIZATION IN BULK ZINCBLENDE AND WURTZITE GAN

In this article, the first calculations of hole initiated interband im pact ionization in bulk zincblende wurtzite phase GaN are presented. T he calculations are made using an ensemble Monte Carlo simulation incl uding the full details of all of the relevant valence bands, derived f rom an empirical pseudopotential approach, for each crystal type. The model also includes numerically generated hole initiated impact ioniza tion transition rates, calculated based on the pseudopotential band st ructure. The calculations predict that both the average hole energies and ionization coefficients are substantially higher in the zincblende phase than in the wurtzite phase. This difference is attributed to th e higher valence band effective masses and equivalently higher effecti ve density of states found in the wurtzite polytype. Furthermore, the hole ionization coefficient is found to be comparable to the previousl y calculated electron ionization coefficient in zincblende GaN at an a pplied electric field strength of 3 MV/cm. In the wurtzite phase, the electron and hole impact ionization coefficients are predicted to be s imilar at high electric fields, but at lower fields, the hole ionizati on rate appears to be greater. (C) 1997 American Institute of Physics.