Invariant Wide Bandgaps in Honeycomb Monolayer and Single-Walled Nanotubes of IIB-VI Semiconductors

Abstract

Search for low-dimensional materials with unique electronic properties is important for the development of electronic devices in nano scale. Through systematic first-principles calculations, we found that the band gaps of the two-dimensional honeycomb monolayers and one-dimensional single-walled nanotubes of IIB-VI semiconductors (ZnO, CdO, ZnS and CdS) are nearly chirality-independent and weakly diameter-dependent. Based on analysis of the electronic structures, it was found that the conduction band minimum is contributed by the spherically symmetric $s$ orbitals of cations and the valence band maximum is dominated by the in-plane $(d_{xy}-p_y)$ and $(d_{x^2-y^2}-p_x)$ hybridizations. These electronic states are robust against radius curvature, resulting in the invariant feature of the band gaps for the structures changing from honeycomb monolayer to single-walled nanotubes. The band gaps of these materials range from 2.3 eV to 4.7 eV, which is of potential applications in electronic devices and optoelectronic devices. Our studies show that searching for and designing specific electronic structures can facilitate the process of exploring novel nanomaterials for future applications.