Hole initiated impact ionization in wide band gap semiconductors

Band-to-band impact ionization by hot electrons and holes is an important p rocess in high-field transport in semiconductors, leading to carrier multip lication and avalanche breakdown. Here we perform first principles calculat ions for the respective microscopic scattering rates of both electrons and holes in various wide band gap semiconductors. The impact ionization rates themselves are calculated directly from the electronic band structure deriv ed from empirical pseudopotential calculations for cubic GaN, ZnS, and SrS. In comparison with the electron rates, a cutoff in the hole rate is found due to the relatively narrow valence bandwidths in these wide band gap semi conductors, which correspondingly reduces hole initiated carrier multiplica tion. (C) 1999 American Institute of Physics. [S0021-8979(99)08419-4].