  Discovery and design of two-dimensional (2D) materials with suitable band
gaps and high carrier mobility is of vital importance for photonics,
optoelectronics, and high-speed electronics. In this work, based on first
principles calculations using density functional theory (DFT) with PBE and HSE
functionals, we introduce a family of monolayer isostructural semiconducting
tellurides M2N2Te8, with M = {Ti, Zr, Hf} and N= {Si, Ge}. These compounds have
been identified to possess direct band gaps from 1.0 eV to 1.31 eV, which are
well suited for photonics and optoelectronics applications. Additionally,
anisotropic in-plane transport behavior is observed and small electron and hole
(0.11 - 0.15 me) effective masses are identified along the dominant transport
direction. Ultra-high carrier mobility is predicted for this family of 2D
compounds which host great promise for potential applications in high-speed
electronic devices. Detailed analysis of electronic structures reveals the
origins of the promising properties of this unique class of 2D telluride
materials.
