Investigation of Anomalous Optical Characteristics of InGaAsP Layers on GaAs Substrates Grown by Metalorganic Vapor Phase Epitaxy

We investigated the growth of InGaAsP layers on GaAs substrates by metalorganic vapor phase epitaxy (MOVPE) for application in optical devices. Anomalous large redshifts of photoluminescence (PL) were observed for samples of specific In1-xGaxAsyP1-y compositions ($x$ and $y$ are approximately 0.85 and 0.65, respectively). We showed that these large redshifts were induced by phase separation in the miscibility gap of InGaAsP. In order to clarify the threshold value of the phase separation that causes this anomalous PL emission, the phase separation was quantified by combining PL spectroscopy and energy dispersive X-ray spectroscopy (EDX). It was found for the first time that PL redshifts start to occur when the phase-separation quantity of the group-III element of In1-xGaxAsyP1-y crystals ($\Delta x$) exceeds ${\sim}0.05$. Such large PL redshifts can be attributed to the emission from defect-related energy levels caused by phase separation.