Evaluation of electron ionization threshold energies for Al_xGa_(1-x)As on a hypercube

摘要

The impact ionization threshold energies for Al_xGa_(1-x)As were evaluated over the entire first Brillouin zone using a 16 node Intel iPSC/860 hypercube. The bandstructures were evaluated using the empirical pseudopotential method and Anderson and Crowell's procedure was used to evaluate the ionization threshold energies. An efficient parallel sorting and searching procedure was used to obtain significant speedups in the calculation. Our results show that while the threshold energy for GaAs, E_(th)(k), is reasonably isotropic over the Brillouin zone, it displays marked anisotropy for Al_xGa_(1-x)As with aluminum mole fraction greater than 0.45 (corresponding to the transition from direct to indirect bandgap material). The results also show that while the use of a constant ionization threshold energy value for GaAs may be a good approximation in carrier transport calculations, it may be necessary to use wavevector dependent threshold energies for Al_xGa_(1-x)As. We believe that this is the first time that such a calculation has been performed over the entire first Brillouin zone in Al_xGa_(1-x)As.