Ordered and disordered two-dimensional tellurium-selenium binary compounds from swarm intelligence and first principles

We explore two-dimensional (2D) binary compounds consisting of selenium and tellurium elements by means of particle swarm optimization, Monte Carlo special quasi-random structures and density functional theory calculations. Three types of stable structures, namely T-, C- and S-phases, are screened from the outputs of crystal search. Based on these three phases, we select five polymorphs to investigate their electronic structure properties and find that all are semiconductors with band gaps ranging from 0.12 to 1.55 eV. Moreover, one may tune the band structures and gap values by changing the stoichiometric proportions, and reveal that binary 2D TeSe materials exhibit potential applications. Interestingly, a band gap at the Dirac point of the S-phase can open up even without consideration of spin orbit coupling, which is explained by a tight-binding model. Further, we construct special quasi-random structures to investigate their corresponding solid solution disordered alloys. Our findings show that the versatile structures of 2D TeSe binary compounds will be useful for electronic materials and device design.