Ultrathin tellurium dioxide: emerging direct bandgap semiconductor with high-mobility transport anisotropy.

An effectively large bandgap and a high carrier mobility of two dimensional (2D) crystals are crucial in emerging materials for nanoelectronics. A previously unexplored two-dimensional material, monolayer TeO2, is proposed to have high stability, a wide direct gap and high carrier mobility, based on first-principles calculations. Our results show that 2D TeO2 is both thermally and dynamically stable. In addition, it is easily exfoliated from its bulk counterpart, a natural layered mineral tellurite. Importantly, 2D TeO2 always exhibits a direct bandgap when thinning from bulk (3.32 eV) to monolayer (3.70 eV), an energy range not covered by previously reported 2D materials. Furthermore, monolayer TeO2 is exceptional in high transport anisotropy, possessing not only high electron mobility (of the order of 1000 cm2 V-1 s-1) but also exceptionally high hole mobility (up to 9100 cm2 V-1 s-1). All these findings make 2D TeO2 a promising candidate for both power electronics and short-wavelength optoelectronic applications.