Composition-Dependent Structural and Gradually Tunable Bandgap of GeS1-xSex Alloys Synthesized via Chemical Vapor Transport

Abstract

Alloy engineering provides an effective strategy to tailor semiconductor properties and expand their functional applicability. The ternary alloy series GeS 1-x Se x (0 ≤ x ≤ 1) were synthesized via chemical vapor transport, and six compositions were prepared to systematically investigate their composition-dependent structural, optical, and electrical properties. X-ray diffraction analysis reveals a continuous alloy series following Vegard's law, with a relatively larger bowing along the zigzag and armchair directions. The Halder-Wagner and size-strain plot analyses identify four distinct strain regimes across the GeS 1-x Se x alloys. At low Se contents (x = 0-0.37), both strain and deformation energy density peak near x = 0.37, indicating pronounced lattice distortion and high stored energy. In the intermediate Se range (x = 0.37-0.61), strain relaxation dominates, facilitated by reduced crystallite size and the emergence of a multi-interfacial crystalline-amorphous structure near x = 0.61 that effectively dissipates deformation energy and enhances structural stability. In the Se-rich regime (x = 0.61-0.85), renewed lattice expansion and heterogeneous distortion regenerate local misfit strain, leading to increased residual stress and dislocation density. As the Se content approaches saturation (x = 0.85-1), the structure no longer generates a substantial number of defects. 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-x Se x alloys, establishing them as promising candidates for tunable optoelectronic applications.