Tunable Electronic Structures upon Janus In2Ge2X3Y3 (X, Y =S, Se and Te) Monolayers by External Fields

Abstract

Two dimensional (2D) materials with ultrathin atomic thicknesses and intriguing properties have aroused tremendous attention. Inspired by emerging researches on 2D InGeX3 (X =S, Se and Te), the novel properties of their Janus structures In2Ge2X3Y3 (X, Y =S, Se and Te) monolayers may be of interest. Here, we explore their geometric structures, stabilities and electronic properties using first-principles calculations. The In2Ge2X3Y3 monolayers are dynamically and thermally stable, and the In-X/Y and Ge-X/Y bonds exhibit ionic bonding characteristics. Our calculations show that In2Ge2X3Y3 possess direct band gaps of 0 to 1.205 eV at PBE level (0.638 to 2.323 eV at HSE level). The sharp band dispersion for electrons induces smaller effective masses than holes, giving rise to mobilities as high as 59-86 cm2 V-1 s-1. Additionally, by adding external strains or electric fields, In2Ge2X3Y3 monolayers exhibit remarkably tunable electronic structures. Especially, the monolayer In2Ge2S3Se3 exhibits a larger band gap, higher carrier transport capability, as well as a wider range of tunable electronic structure compared to In2Ge2S3Te3 and In2Ge2Se3Te3. The findings in this work establish a fundamental physical understanding of 2D Janus In2Ge2X3Y3, which can promote the future synthesis, characterization, and application of these 2D materials.