Bulk beta-Te to few layered beta-tellurenes: indirect to direct band-Gap transitions showing semiconducting property

Herein we report a prediction of a highly kinetic stable layered structure of tellurium (namely, bulk beta-Te), which is similar to these layered bulk materials such as graphite, black phosphorus, and gray arsenic. Bulk beta-Te turns out to be a semiconductor that has a band gap of 0.325 eV (HSE06: 0.605 eV), based on first-principles calculations. Moreover, the single-layer form of the bulk beta-Te, called beta-tellurene, is predicted to have a high stability. When the bulk beta-Te is thinned to one atomic layer, an indirect semiconductor of band gap is changed to 1.265 eV (HSE06: 1.932 eV) with a very high kinetic stability. Interestingly, an increase of the number of the beta-tellurene layers from one to three is accompanied by a shift from an indirect to direct band gap. Furthermore, the effective carrier masses, the optical properties and phonon modes of few-layer beta-tellurenes are characterized. Few-layer beta-tellurenes strongly absorb the ultraviolet and blue-violet visible lights. The dramatic changes in the electronic structure and excellent photo absorptivities are expected to pave the way for high speed ultrathin transistors, as well as optoelectronic devices working in the UV or blue-green visible regions.