In contrast to pseudobinary alloys, the relative number of bonds in quaternary alloys cannot be determined uniquely from the composition. Indeed, we do not know if the ${\mathrm{Ga}}_{0.5}{\mathrm{In}}_{0.5}{\mathrm{As}}_{0.5}{\mathrm{N}}_{0.5}$ alloy should be thought of as $\mathrm{InAs}+\mathrm{GaN}$ or as $\mathrm{InN}+\mathrm{GaAs}$. We study the distribution of bonds using Monte Carlo simulation and find that the number of In-N and Ga-As bonds increases relative to random alloys. This quaternary-unique short range order affects the band structure: we calculate a blueshift of the band gap and predict the emergence of a broadband tail of localized states around the conduction band minimum.

• Received 14 August 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.2609