Tunable electronic structures of Janus In2Ge2X3Y3 (X, Y = S, Se and Te) monolayers under external fields

Two dimensional (2D) materials with ultrathin atomic thicknesses and intriguing properties have aroused tremendous attention. Inspired by emerging research studies on 2D InGeX3 (X = S, Se and Te), the novel properties of Janus In2Ge2X3Y3 monolayers are 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 monolayers possess direct band gaps of 0 to 1.205 eV at the PBE level (0.638 to 2.323 eV at the HSE level). The sharp band dispersion of electrons induces smaller effective masses than that of holes, giving rise to mobilities as high as 59-86 cm(2) V-1 s(-1). Additionally, upon application of external strain or electric fields, In2Ge2X3Y3 monolayers exhibit remarkably tunable electronic structures. Especially, the monolayer In2Ge2S3Se3 exhibits a larger band gap, higher carrier transport capability, and a wider range of tunable electronic structures compared to In2Ge2S3Te3 and In2Ge2Se3Te3 monolayers. The findings in this work establish a fundamental physical understanding of 2D Janus In2Ge2X3Y3 monolayers, which can promote the future synthesis, characterization, and application of these 2D materials.