Structural, electronic and magnetic properties of group III monochalcogenide nanoribbons

Abstract

Owing to the promising optoelectronic and thermoelectric properties of two-dimensional (2D) group III–VI materials (MXs), their nanoribbons (NRs) have attracted notable attention as an emerging class of quasi-one-dimensional (quasi-1D) nanostructures. Due to the fact that the most stable 2D monolayer polymorph of MXs is the 1H phase, to date, existing studies in the literature have predominantly focused on the NRs formed from 1H phase MXs. Nevertheless, NRs of the 1T phase have received little to no attention. Employing ab initio simulations based on density functional theory, we systematically compared the thermodynamic stability of hydrogen-passivated and unpassivated 1T and 1H zigzag (ZNR) and armchair (ANR) edge NRs of GaS, GaSe, and InSe. Our results reveal that nonpolar 1T phase MX ZNRs are thermodynamically more favorable than polar 1H MX ZNRs at widths up to 34 nm, a range that is realizable through contemporary experimental fabrication techniques. On the other hand, as both 1H and 1T ANRs are nonpolar, 1T is more favorable only in unpassivated cases in very narrow widths of up to 3.3nm in the case of InSe ANRs. Furthermore, unlike metallic 1H ZNRs, 1T ZNRs remain semiconductors and retain Mexican-hat-shaped (MHS) top valence bands. Complementarily, hydrogenation energies of 1T InSe NRs are positive, and due to the edge-localized states, the 1T unpassivated ZNRs possess nearly flat top valence bands. These electronic properties present compelling opportunities for exploiting 1T MX NRs in spintronic applications. We demonstrate that, upon hole doping, these MX NRs develop itinerant magnetization across a broad range of carrier densities and display half-metallic behavior, with only one spin channel intersecting the Fermi level. Moreover, the spin-polarization energies (SPE) of these NRs increase remarkably relative to their 2D counterparts, indicating stronger stability of the ferromagnetic state. We elucidate that the SPE of NRs strongly depends on the degree of edge-localization of the carriers along the width of NRs, which in turn depends on the edge passivation, width, and edge shape of NRs. Overall, this study highlights the critical interplay between the thermodynamic favorability of the novel 1T phase MX NRs below certain critical widths and the resulting electronic and magnetic properties, which together enable their promising applications in spintronics and nanoelectronics.