GeP3: A small indirect band gap 2D crystal with high carrier mobility   and strong interlayer quantum confinement
  We propose a two-dimensional crystal which possesses low indirect band gaps of 0.55 eV (monolayer) and 0.43 eV (bilayer) and high carrier mobilities similar to those of phosphorene: GeP3. GeP3 has a stable three-dimensional layered bulk counterpart which is metallic and is known from experiment since 1970. It has a small cleavage energy, which suggests exfoliation of bulk material as viable means for the preparation of mono- and few-layer materials. The material shows strong interlayer quantum confinement effects, resulting in a band gap reduction from mono- to bilayer, and then to a semiconductor-metal transition between bi- and triple layer. Under biaxial strain, the indirect band gap can be turned into a direct one. Pronounced light absorption in the spectral range from ~600 to 1400 nm is predicted for monolayer and bilayer and promises applications in photovoltaics. 
Yu Jing (1 and 3), Yandong Ma (1), Yafei Li (2), and Thomas Heine (1   and 3) ((1) Wilhelm-Ostwald-Institut f\"ur Physikalis...
cond-mat.mtrl-sci