Quantum conductance of defected phosphorene and germanene nanoribbons

The electronic and transport properties of the monolayer black phosphorus and germanene nanoribbons are studied in the framework of the tight-binding model (TBM) based upon Landauer-Büttiker formalism using Green's function method (GFM). The local density of states (LDOS) and electronic conductance of the phosphorene and germanene nanoribbons along zigzag and armchair directions are examined when the various types of defects are introduced into the system. It is found that the transport properties of zigzag phosphorene and germanene nanoribbons are strongly dependent on the number and location of the vacancies. Furthermore, it is shown that the one-/three-atom vacancy induces quasi-states in the conductance around the Fermi energy because of breaking the sublattice symmetry in the zigzag germanene nanoribbons (ZGeNRs). So the metal-semiconductor transition occurs when one-/three-atom vacancy is located at the edges of ZGeNRs; however, this transition is not observed in the zigzag phosphorene nanoribbons (ZPNRs). Besides, the results of the calculations indicate more sensitivity of ZPNRs on conductivity to the edge vacancy disorders than armchair phosphorene nanoribbons (APNRs). In addition, the conductance of ZPNRs decreases with the increment of the ribbon width in the presence of edge vacancy. Importantly, the disappearance of conductance around Fermi energy in ZPNR due to Anderson localization disorder highlights an important conclusion for the possibility of quenching of the conductance near the Fermi energy, making this class of materials appealing for applications in digital transistor devices.