First-Principles Prediction of β-phase SnA2N4 (A = Si; Ge) Monolayers: Outstanding Mechanical Anisotropy and High Electron Mobility for FET Devices

Abstract

The recently synthesized monolayer MoSi2N4 (Science 2020, 369, 670) boasts extraordinary environmental stability and superior comprehensive performance, offering exciting opportunities for the exploration of two-dimensional MX2Z4 materials. However, the low carrier mobility of α-MoSi2N4 significantly limits its practical applications in field-effect transistor (FET) devices. In this study, first-principles calculations were utilized to systematically investigate the structural stability, photoelectronic properties, tensile mechanical behavior, and carrier mobility of a novel family of β-SnA2N4 (A = Si, Ge) monolayers. Our findings reveal that these β-SnA2N4 monolayers demonstrate remarkable dynamic and thermal stability. Specifically, calculations based on the HSE06 functional reveal that the SnSi2N4 and SnGe2N4 monolayers are semiconductors with band gaps of 3.36 eV and 2.13 eV, respectively. Additionally, the SnA2N4 monolayers exhibit distinct mechanical anisotropy, characterized by high ideal tensile strengths and critical tensile strains exceeding 27%, indicating outstanding ductility. Importantly, the SnA2N4 monolayers display exceptional anisotropic in-plane charge transport, achieving electron mobility level of up to 103 cm2V-1s-1, surpassing those of the α-phase MA2N4 (M = Mo, W; A = Si, Ge) monolayers. These novel ternary monolayer structures are expected to enrich the 2D MA2Z4 material family and emerge as promising candidates for FET applications.