  Significant efficiency droop is a major concern for light-emitting diodes and
laser diodes operating at high current density. Recent study has suggested that
heavily Bi-alloyed GaAs can decrease the non-radiative Auger recombination and
therefore alleviate the efficiency droop. Using density functional theory, we
studied a newly fabricated quaternary alloy, GaAs1-x-yPyBix, which can host
significant amounts of Bi, through calculations of its band gap, spin-orbit
splitting, and band offsets with GaAs. We found that the band gap changes of
GaAs1-x-yPyBix relative to GaAs are determined mainly by the local structural
changes around P and Bi atoms rather than their electronic structure
differences. To obtain alloy with lower Auger recombination than GaAs bulk, we
identified the necessary constraints on the compositions of P and Bi. Finally,
we demonstrated that GaAs/GaAs1-x-yPyBix heterojunctions with potentially low
Auger recombination can exhibit small lattice mismatch and large enough band
offsets for strong carrier confinement. This work shows that the electronic
properties of GaAs1-x-yPyBix are potentially suitable for high-energy infrared
light-emitting diodes and laser diodes with improved efficiency.
