A composition-dependent structural and gradually tunable bandgap of GeS1−xSex alloys synthesized via chemical vapor transport

Abstract

Alloy engineering provides new insight into strain-mediated property tuning in anisotropic layered semiconductors and expands their functional applicability. The ternary alloy series GeS_1−xSe_x (0 ≤ x ≤ 1) were synthesized via chemical vapor transport to systematically investigate lattice strain evolution, bandgap modulation, and electrical properties. The strain evolution in GeS_1−xSe_x alloys exhibits a transition from strain accumulation to strain relaxation with increasing Se content. At low Se compositions (x = 0–0.37), lattice strain and deformation energy increase and peak at x = 0.37, indicating the most pronounced lattice distortion and stored deformation energy. As the Se content increases to the intermediate composition range (x = 0.37–0.61), strain relaxation becomes dominant, accompanied by crystallite size reduction and the emergence of a strain-disordered crystalline structure with abundant interfacial regions near x = 0.61. This structural evolution effectively dissipates accumulated deformation energy, redistributes internal stress, and leads to enhanced structural stability. The optical absorption spectra exhibit a gradual redshift in bandgap energies from 1.60 eV (GeS) to 1.15 eV (GeSe), in close agreement with Vegard's law. Correspondingly, electrical measurements show a marked decrease in resistivity beyond x = 0.21, reaching a minimum value of 0.144 Ω m for GeSe. Overall, these findings demonstrate that Se substitution effectively tunes the lattice strain, bandgap, and conductivity of GeS_1−xSe_x alloys, establishing them as promising candidates for tunable optoelectronic applications.