Structure and properties of intrinsic and extrinsic defects in black phosphorus.

Julian Gaberle,Alexander L Shluger

doi:10.1039/c8nr06640j

Abstract

The electronic and geometric structures of a range of intrinsic and extrinsic defects in black phosphorus (BP) are calculated using Density Functional Theory (DFT) and a hybrid density functional. The results demonstrate that energy barriers to form intrinsic defects, such as Frenkel pairs and Stone-Wales type defects, exceed 3.0 eV and their equilibrium concentrations are likely to be low. Therefore, growth conditions and sample preparation play a crucial role in defect chemistry of black phosphorus. Mono-vacancies (MV) are shown to introduce a shallow acceptor state in the bandgap of BP, but exhibit fast hopping rates at room temperature. Coalescence of MVs into di-vacancies (DV) is energetically favourable and eliminates the band gap states. Thus MVs are not likely to be the main contributor to p-doping in BP. Extrinsic defects are a plausible alternative, with SnP found to be the most promising candidate. Other defects considered include I, O, Fe, Cu, Zn and Ni in surface adsorbed, intercalated and substitutional geometries, respectively. Furthermore, BP was found to be magnetic for isolated MVs and Fe doping, motivating further research in the area of magnetic functionalisation.

Highlights

Black Phosphorus (BP) has been the subject of intense research in the past few years, since it was rediscovered as a 2D material
As a layered 2D material, it exhibits a change in physical properties going from bulk crystal to the nanoscale single layer limit: the bandgap opens from 0.3 eV for bulk BP to 1.5 eV for a single layer due to the suppression of interlayer interactions.[8]
Our results show the dependence of defect geometries and their electronic signature on the number of BP layers and will provide a theoretical background to support future experiments

Summary

Introduction

Black Phosphorus (BP) has been the subject of intense research in the past few years, since it was rediscovered as a 2D material. As a layered 2D material, it exhibits a change in physical properties going from bulk crystal to the nanoscale single layer limit: the bandgap opens from 0.3 eV for bulk BP to 1.5 eV for a single layer due to the suppression of interlayer interactions.[8] Similar to graphene, BP has very high charge carrier mobilities of up to 200–1000 cm[2] V−1 s−1 and displays anisotropic behaviour along the Γ–X and Γ–Y principal directions in many of its properties.[9] due to lone pairs pointing outwards from the surface, BP is highly reactive with oxygen, which makes its properties sensitive to ambient conditions.[10,11] The rapid oxidation of BP can be prevented by capping layers,[12,13] and the stability and performance for future applications depends on intrinsic defects such as point defects, line defects and impurities. The development of novel devices is mostly hindered by the lack of understanding of defects and defect creation.[14]

Methods

Results

Discussion

Conclusion