Composition-dependent photoluminescence and effective electron-phonon coupling parameters in metamorphic InAsP buffer layers

Step-graded InAs x P 1 − x metamorphic buffer layers (MBLs) grown on InP are essential virtual substrates for lattice-mismatched III-V optoelectronic devices, yet their composition-dependent electron-phonon interactions remain poorly investigated. Here, the structural, optical, and electronic properties of InAsP/InP MBLs with topmost-layer A s compositions of x = 0.62 , 0.76 , and 0.81 were systematically investigated using high-resolution X-ray diffraction (HRXRD), temperature-dependent photoluminescence (TDPL), and qualitative first-principles density functional theory. HRXRD results showed a reduction in rocking-curve full width at half maximum with increasing A s composition, indicating improved crystalline quality. Symmetric and asymmetric reciprocal-space maps demonstrated low residual strain and a decrease in it with increasing A s composition, together with a very low average MBL tilt. TDPL analysis using the O’Donnell–Chen model showed that both the effective phonon energy and the effective electron-phonon coupling associated with the temperature-induced renormalization of the PL transition energy decrease systematically with increasing A s content. To obtain an electronic-structure perspective on this trend, density of states, charge-density isosurfaces, and inverse participation ratio analyses were performed using Quantum ESPRESSO and the special quasirandom structure method. The calculations indicated progressively more delocalized band-edge states with increasing A s composition, providing a possible electronic-structure correlate of the experimentally observed reduction in the TDPL-derived effective coupling parameter. These findings suggest a composition-dependent correlation between alloy composition, wavefunction localization, and phonon-coupled optical properties. Quantitative determination of the underlying electron-phonon matrix elements remains beyond the scope of this study.