Optical transitions and localized edge states in skewed zigzag phosphorene nanoribbons

Using the Tight Binding (TB) parameters extracted from Density Functional Theory (DFT) and Recursive Green's Function method (RGF), it is shown that skewed-zigzag black phosphorus (phosphorene) nanoribbons obtain large and tuneable bandgap in response to vertical and transverse electric fields. Depending on the direction of the applied field the mid-gap states could possess the localized or metallic nature i.e., non-zero mid-gap density of states. Adjustability of the bandgap and optical dipole transition matrix elements are explained based on the symmetry of involved band edge states. This promises new electronic and optical devices based on phosphorene nanoribbons.