Biaxial strain modulated valence-band engineering in III-V digital alloys

A series of III-V digital alloy avalanche photodiodes have been recently seen to exhibit very low excess noise. These alloys have low hole ionization coefficients due to enhanced effective mass, a large separation between light-hole and split-off bands in the valence band, and in one case (InAlAs), potentially the creation of a small minigap in computed band structures. Whereas such minigaps would indeed provide a reliable way to suppress hole transport and reduce excess noise, their physical origin is explored here. In this paper, we provide an explanation for the formation of the minigaps as arising from oscillations in certain orbital overlaps. We demonstrate that decreasing the substrate lattice constant would increase the minigap size and mass in the transport direction. This leads to reduced quantum tunneling and phonon scattering of the holes. Finally, we illustrate the band-structure modification with substrate lattice constant for other III-V digital alloys. We, thus, provide a recipe for deterministic engineering of sizable valence-band minigaps as a potential recipe for high gain avalanche photodiodes.