Structural landscape of two-dimensional phases in group II–VI semiconductors

Abstract

Group II–VI semiconductors, renowned for their direct band gaps, high carrier mobilities, and mature synthesis, are essential in optoelectronic applications. While scaling down to the two-dimensional (2D) limit could unlock enhanced and distinct functionalities, realizing stable intrinsic 2D phases remains challenging due to their nonlayered bulk structures, strong interlayer covalency, and high ionicity. Here, using first-principles calculations, we demonstrate that II–VI compounds adopt stable 2D configurations distinct from both graphene-like sheets and bulk fragments. The most stable phases identified include tetragonal–triangle, double-layer honeycomb, planar honeycomb, and a non-conventional bilayer. Despite being isoelectronic, these compounds exhibit markedly different energetic landscapes. We propose that this diversity originates from a dual competing mechanism: the geometric stability imparted by favorable building blocks vs the long-range Coulomb interactions. Several predicted structures exhibit excellent electronic properties, with computed mobilities exceeding 29 000 cm2 V−1 s−1 in CdS, highlighting their potential for nanoelectronic applications. Our findings provide both a structural design rule and a set of experimentally accessible targets, offering a pathway toward integrating II–VI semiconductors into the 2D material landscape.