Interface Engineering in MOCVD‐Grown Multi‐Composition InGaAs/InAlAs Superlattices for 4.6 µm Step‐Tapered Active Region QCLs

Quantum‐cascade‐laser (QCL) performance depends on the sharpness of sub‐nanometer hetero‐interfaces repeated hundreds of times, yet the growth parameters governing interface formation in metal–organic‐chemical‐vapor‐deposition (MOCVD) grown InGaAs/InAlAs structures remain poorly understood for advanced multi‐composition designs. In this study, superlattices containing three InGaAs‐well and three InAlAs‐barrier compositions, representing a 4.6 µm step‐tapered‐QCL active region, were grown on InP by MOCVD. The effects of AsH 3 flow, growth interruption time, net strain, and interface number on interface and surface quality were examined by high‐resolution X‐ray diffraction (HR‐XRD), X‐ray reflectivity (XRR), atomic force microscopy (AFM), Raman spectroscopy, and photoluminescence (PL). The results suggest that AsH 3 flow governs the balance between surface As coverage and group‐III adatom diffusion, with the mostbalanced behavior at 30 sccm. Comparing interruption times revealed a trade‐off, attributed to In segregation, between interface sharpness and surface smoothness: a short interruption (3 s) preserved sharp interfaces, while a longer one (5 s) produced smoother surfaces, which we attribute to strain energy dissipation through limited interface broadening. This behavior was independently reproduced in a strain‐balanced structure, consistent with a single underlying mechanism. In a structure with halved layer thicknesses and doubled interface number, sharp satellite peaks, and step‐flow morphology persisted even at the 2–3 monolayer level. These findings provide a physically guided basis and a step toward a transferable process for interface engineering in multi‐composition QCL active regions.