Origin of Intrinsic Direct Band Gap of Janus Group-III Chalcogenide Monolayers

Using first-principles calculations, the evolution of electronic properties of InSe based Janus structures has been investigated. The obtained results suggest that the In2SeTe Janus structure has an intrinsic direct band gap which is beneficial for optoelectronic applications. The direct band gap nature of In2SeTe Janus structure is due to the strong coupling of p(z) orbitals between the Se and Te sublayers, which emphasizes the importance of the intra-layer interactions. In addition, the effective mass of the holes in In2SeTe is one order of magnitude smaller than that of intrinsic InSe monolayer, which makes it a good candidate for p-type semiconductor. The broken mirror symmetry of the Janus structures induces out-of-plane dipolar polarization, yielding additional built-in electric field and offering extra channel to tune its electronic band structure. The electric field has dominated effluences on the charge polarization on anions thus exhibiting stronger band tunability on the valence bands. These results indicate that the preparation of In2SeTe Janus structure provides a new way for the future use of two-dimensional materials in optoelectronic nanodevices.