Properties of bismuth based Bi2A3 (A = S, Se, Te) chalcogenides for optoelectronic and thermoelectric applications

Structural, electronic, optical, mechanical, thermoelectric and dielectric properties of binary Bi₂A₃ (A = S, Se, Te) chalcogenide semiconductors are studied by first-principles approach. Bismuth sulfide (Bi₂S₃) is found to be structurally stable in orthorhombic structure while bismuth selenide (Bi₂Se₃) and bismuth telluride (Bi₂Te₃) are stable in trigonal structure. Calculated mechanical properties reveal that all three Bi₂A₃ (A = S, Se, Te) compounds fulfil the mechanical stability criteria. Band structure calculations reveal that the Bi₂S₃ exhibits direct optical band gap (E_g = 1. 58 eV) which lies in the near-infrared (NIR) region, while the calculated E_g of Bi₂Se₃ and Bi₂Te₃ are found to be 0.53 eV and 0.35 eV, respectively lying in the far-infrared region. For Bi₂S₃ and Bi₂Se₃ compounds, the calculated dielectric properties show strong anisotropic behavior, while negligible anisotropic dielectric behavior is observed for Bi₂Te₃. Calculated optical properties show that all three Bi₂A₃ compounds possess high absorption coefficient (> 10⁴ cm⁻¹). For all three Bi₂A₃ (A = S, Se, Te) compounds, the calculated optical conductivity show prominent peak corresponding to the occurrence of optical conduction at energies 3.36 eV, 2.65 eV and 2.02 eV respectively. Calculated optical results support the results deduced from band structures and density of states spectra. Optical properties and dielectric behavior suggest that the Bi₂S₃ compound has suitable band gap and has potential to use for photovoltaic applications while Bi₂A₃ (A = Se, Te) compounds could be used in infrared detectors and other optical devices. Calculated thermal properties reveal that the Bi₂A₃ (A = S, Se, Te) chalcogenides could be potential materials for thermoelectric applications.