Thickness-Dependent Optical Properties and Exciton Recombination Dynamics in the GaSe_0.5Te_0.5 Alloy

In this study, we investigate the thickness-dependent optical properties of GaSe_0.5Te_0.5 alloy by combining Raman spectroscopy, photoluminescence (PL) measurements, and density functional theory (DFT) calculations. Raman measurements reveal thickness-dependent variations in phonon frequencies and intensities below ∼20 nm, enabling thickness identification through frequency differences between phonon modes. In addition, PL measurements show a pronounced quenching of the PL intensity with decreasing thickness, attributed to enhanced nonradiative recombination associated with surface states and thickness-induced modifications of the electronic structure, accompanied by a blueshift of the PL energy. In agreement with these observations, first-principles calculations demonstrate a thickness-driven evolution of the band structure, with a transition from an indirect character in few-layer systems toward a more direct gap in thicker structures, governed by the interplay between quantum confinement and interlayer coupling. Complementary excitation-power-dependent PL measurements further show distinct recombination dynamics in bulk samples, with sublinear behavior for trapped excitons and superlinear dependence for bound and free excitons, consistent with a state-filling mechanism in localized states. These findings establish a consistent framework linking thickness, electronic structure, and recombination processes in GaSe_0.5Te_0.5 alloy, and provide key insights for the design and optimization of optoelectronic devices based on PTMC alloys.