Bi2Te2Se and Sb2Te3 heterostructure based photodetectors with high responsivity and broadband photoresponse: experimental and theoretical analysis

Topological insulators have emerged as one of the most promising candidates for the fabrication of novel electronic and optoelectronic devices due to the unique properties of nontrivial Dirac cones on the surface and a narrow bandgap in the bulk. In this work, the Sb₂Te₃ and Bi₂Te₂Se materials, and their heterostructure are fabricated by metal–organic chemical vapour deposition and evaporation techniques. Photodetection of these materials and their heterostructure shows that they detect light in a broadband range of 600 to 1100 nm with maximum photoresponse of Sb₂Te₃, Bi₂Te₂Se and Sb₂Te₃/Bi₂Te₂Se at 1100, 1000, and 1000 nm, respectively. The maximum responsivity values of Sb₂Te₃, Bi₂Te₂Se, and their heterostructure are 183, 341.8, and 245.9 A W⁻¹ at 1000 nm, respectively. A computational study has also been done using density functional theory (DFT). Using the first-principles methods based on DFT, we have systematically investigated these topological insulators and their heterostructure's electronic and optical properties. The band structures of Sb₂Te₃ and Bi₂Te₂Se thin films (3 QL) and their heterostructure are calculated. The bandgaps of Sb₂Te₃ and Bi₂Te₂Se are 26.4 and 23 meV, respectively, while the Sb₂Te₃/Bi₂Te₂Se heterostructure shows metallic behaviour. For the optical properties, the dielectric function's real and imaginary parts are calculated using DFT and random phase approximation (RPA). It is observed that these topological materials and their heterostructure are light absorbers in a broadband range, with maximum absorption at 1.90, 2.40, and 3.21 eV.