Effect of molecular beam epitaxy growth conditions on phase separation in wide-bandgap InAlAsSb lattice-matched to InP

In_xAl_1-xAs_1-ySb_y is the only III-V material lattice-matched to InP with a direct bandgap energy range as large as ~1.45–1.80 eV, making it interesting for multiple optoelectronic applications. However, inherent material challenges in this immature quaternary alloy have thus far precluded the growth of In_xAl_1-xAs_1-ySb_y with device-quality properties at the InP lattice constant. We have investigated how molecular beam epitaxy growth conditions affect the photoluminescence intensity, spectrum, temperature- and power-dependence, as well as the surface morphology of In_0.23Al_0.77As_0.75Sb_0.25, which is lattice-matched to InP with bandgap energy of ~1.68 eV as measured by ellipsometry. We find that reducing the adatom mobility, via a lower substrate temperature and higher group-V overpressure, diminishes the tendency for phase separation, but also quenches the photoluminescence intensity. These findings provide a step toward identifying an optimal growth window for realizing high-quality, wide-bandgap In_xAl_1-xAs_1-ySb_y lattice-matched to InP.