Theoretical study of structural, electronic and optical properties of bismuth-selenide, bismuth-telluride and antimony-telluride/graphene heterostructure for broadband photodetector

Abstract

It remains challenging to produce high-performance broadband photodetector that can detect light from infrared to ultraviolet frequency range for biomedical imaging, gas sensing and optical communication applications. In particular, large energy band gap and low optical absorption in the material utilized as absorbing layer have prevented a report of high performance broadband photodetector in terms of quantum efficiency and photoresponsivity. However, integrating second generation topological insulators (2GTI), namely, bismuth selenide (Bi2Se3), bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) with graphene in a heterostructure appears to be the more promising approach. In this heterostructure, optical absorption takes place in 2GTI while graphene acts as charge carrier collector owing to its high carrier mobility. Therefore, detailed knowledge of the design, as well as structural, electronic and optical properties of 2GTI/graphene heterostructures, is essential to expose their hidden potentials. Structural properties of Bi2Se3, Bi2Te3, and Sb2Te3 are studied by first-principles calculations within density functional theory (DFT) framework. Many-body perturbation theory (MBPT) based one-shot GW (G0W0) and Bethe-Salpeter equation (G0W0-BSE) approaches were used to compute the quasiparticle (QP) band structure, excitonic and optical properties. The DFT calculations show that inclusion of van der Waals (vdW) correction with most recent developed Coope’s exchange (vdW-DFC09x) reproduce experimental interlayer distances, lattice parameters and atomic coordinates of Bi2Se3, Bi2Te3 and Sb2Te3 2GTI. The one-shot GW calculations confirm that Bi2Se3 and Sb2Te3 are direct band gap materials with band gap values of 0.36 eV and 0.22 eV while Bi2Te3 is indirect band gap material with 0.17 eV energy band gap. The results on the optical properties of 2GTI with inclusion of electron-hole interaction show that the exciton energy for Bi2Se3, Bi2Te3, and Sb2Te3 are 0.28, 0.14 and 0.19 eV respectively while their corresponding plasma energies are 16.4, 15.6 and 9.6 eV respectively. These values show that the investigated materials can absorb photons within broadband wavelengths. For the design, the energy analysis of Sb2Te3/graphene heterostructure reveals that the most stable configuration is the one in which the Te-1 atom of Sb2Te3 facing to graphene is above the hole centre of graphene’s hexagonal lattice. More attractively, the system of Sb2Te3/graphene heterostructure shows that strong hybridization between Sb2Te3 and graphene at smaller interlayer distance resulted in an energy gap at the Dirac states. It is, therefore, anticipated that this heterostructure will be useful for new-generation optoelectronic applications particularly in broadband photodetectors.