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.