Piezoelectricity and optical properties of janus MXY (M = Sb, As; X = Te, Se; Y = Br, I) monolayers

Abstract

Two-dimensional (2D) piezoelectric semiconductor nanomaterials with strong optical absorbance in the visible range are promising applications in piezotronics, phototronics, and piezo-phototronics. We determine and analyze the stability, electronic structures, piezoelectricity, and optical properties of MXY (M = Sb, As; X = Te, Se; Y = Br, I) monolayers. Analyses of stabilities disclose these monolayers are energetically, mechanically, thermodynamically, and dynamically stable. Both HSE06-SOC and G0W0 approaches reveal that all the monolayers have indirect gaps falling in the visible optical spectrum. The intrinsic mirror asymmetry not only induces appreciable in-plane and vertical piezoelectricity, which is comparable with the Janus transition metal dichalcogenide monolayers, but also exhibit appreciable intrinsic build-in electronic field. The robust excitonic effects shift the optical absorption spectra down to the visible light region and extend to the ultraviolet region for these monolayers. Finally, the monolayers show large in-plane and out-of-plane static dielectric constants which are larger than most reported monolayers. All the excellent properties suggest that the monolayers are potential candidates for piezotronics, piezo-phototronics, and optoelectronic devices for harvesting solar energy.