Oxygen functionalized InSe and TlTe two-dimensional materials: transition from tunable bandgap semiconductors to quantum spin Hall insulators

From first-principles calculations, we found that oxygen functionalized InSe and TlTe two-dimensional materials undergo the following changes with the increased concentrations of oxygen coverage, transforming from indirect bandgap semiconductors to direct bandgap semiconductors with tunable bandgap, and finally becoming quantum spin hall insulators. The maximal nontrivial bandgap are 0.121 and 0.169 eV, respectively, which occur at 100% oxygen coverage and are suitable for applications at room temperature. In addition, the topological phases are derived from SOC induced p–p bandgap opening, which can be further determined by Z(2) topological invariants and topologically protected gapless edge states. Significantly, the topological phases can be maintained in excess of 75% oxygen coverage and are robust against external strain, making the quantum spin hall effect easy to achieve experimentally. Thus, the oxygen functionalized InSe and TlTe are fine candidate materials for the design and fabrication of topological devices.