Electronic Structure of Monolayer and Bilayer Black Phosphorus with Charged Defects

TL;DR

This study investigates how charged defects affect the electronic properties of monolayer and bilayer black phosphorus using atomistic simulations, revealing anisotropic defect states and substrate effects.

Contribution

It combines first-principles and tight-binding methods to analyze defect-induced electronic states and compares different defect types and substrate influences in black phosphorus.

Findings

Charged defects create anisotropic, distorted hydrogenic orbitals.

Binding energies depend on defect height and substrate dielectric constant.

Intercalants produce more prominent features in local density of states.

Abstract

We use an atomistic approach to study the electronic properties of monolayer and bilayer black phosphorus in the vicinity of a charged defect. In particular, we combine screened defect potentials obtained from first-principles linear response theory with large-scale tight-binding simulations to calculate the wavefunctions and energies of bound acceptor and donor states. As a consequence of the anisotropic band structure, the defect states in these systems form distorted hydrogenic orbitals with a different ordering than in isotropic materials. For the monolayer, we study the dependence of the binding energies of charged adsorbates on the defect height and the dielectric constant of a substrate in an experimental setup. We also compare our results to an anisotropic effective mass model and find quantitative and qualitative differences when the charged defect is close to the black phosphorus or when the screening from the substrate is weak. For the bilayer, we compare results for charged adsorbates and charged intercalants and find that intercalants induce more prominent secondary peaks in the local density of states because they interact strongly with electronic states on both layers. These new insights can be directly tested in scanning tunneling spectroscopy measurements and enable a detailed understanding of the role of Coulomb impurities in electronic devices.