MOVPE growth and optimization of In_xAl_1-xAs layers on InP for high-performance quantum cascade lasers

In this work, we explored the impact of indium composition (x) on the structural and optical characteristics of InxAl1-xAs layers within the context of quantum cascade laser (QCL) structures grown on InP (100) substrates using the Metal Organic Vapor Phase Epitaxy method. The quality of the InxAl1-xAs QCL is notably influenced by the growth with low indium composition, evident in terms of crystallinity, interface sharpness, and optical properties. The properties of the InAsP layer at the InP/InxAl1-xAs junction are particularly sensitive to the indium composition. A drop below 0.52 in indium composition leads to a substantial lattice mismatch between the InxAl1-xAs layer and the InP substrate, typically exceeding [3 8]%. This mismatch induces defects or traps within the bandgap, significantly impacting carrier localization in this system. Our study demonstrates that cultivating InxAl1-xAs with a low indium concentration results in a strained (lattice-mismatched) InxAl1-xAs layer. This finding is significant as it can be leveraged to balance strain in high indium content InGaAs layers, particularly in the context of applications involving quantum cascade lasers.