Kagome-like group-VA monolayers with indirect-direct band gap transition and anisotropic mobility

Based on first-principles calculations and the structural search method, we report a family of novel two-dimensional (2D) materials composed of group-VA elements (P, As, Sb) which share a unique buckled kagome lattice. These new kagome-like phases are intrinsic indirect-gap semiconductors with appropriate band gaps of around 1.6-1.9 eV and demonstrate excellent optical response in the visible light range. More importantly, the band gaps can be flexibly regulated via strain engineering, and an indirect-direct band gap transition can be achieved. The underlying mechanism of this transition is further revealed based on the bonding nature of the near-band-edge electronic orbitals. In addition, the rich gap structure for nanoribbons with zigzag and armchair shaped edges is obtained. Such rich and tunable electronic structures with remarkable anisotropy in kagome-like group-VA materials could pave the way for transistors with high on/off ratios, optoelectronic devices and mechanical sensors based on new 2D crystals. In this article we report the strain-induced indirect-direct band gap transitions in kagome-P, As and Sb.