Thermodynamics of carbon point defects in hexagonal boron nitride

Marek Maciaszek,Audrius Alkauskas,Lukas Razinkovas

doi:10.1103/physrevmaterials.6.014005

Abstract

We present a first-principles computational study of the thermodynamics of carbon defects in hexagonal boron nitride (hBN). The defects considered are carbon monomers, dimers, trimers, and larger carbon clusters, as well as complexes of carbon with vacancies, antisites, and substitutional oxygen. Our calculations show that monomers ($\text{C}_{\text{B}}$, $\text{C}_{\text{B}}$), dimers, trimers, and $\text{C}_{\text{N}}\text{O}_{\text{N}}$ pairs are the most prevalent species under most growth conditions. Compared to these defects, larger carbon clusters, as well as complexes of carbon with vacancies and antisites, occur at much smaller concentrations. Our results are discussed in view of the relevance of carbon defects in single-photon emission in hBN.

Highlights

Over the past two decades, hexagonal boron nitride has gained significant interest both as an insulator used in conjunction with other layered two-dimensional (2D) materials [1] and as an active optical medium itself [2]
We presented the thermodynamic analysis of carbon defects in hexagonal boron nitride
Our particular focus was the relevance of these results to single-photon emission in hexagonal boron nitride (hBN), where the involvement of carbon defects was reported [13]

Summary

Introduction

Over the past two decades, hexagonal boron nitride (hBN) has gained significant interest both as an insulator used in conjunction with other layered two-dimensional (2D) materials [1] and as an active optical medium itself [2]. For all potential applications of hBN, whether as a passive insulator or as an active optoelectronic material, the purity of single crystals or epitaxial layers is crucial. Experiments on bulk hBN samples produced by high-pressure high-temperature synthesis with barium boron nitride (Ba-BN) as a solvent [5], a frequently employed growth method, showed the existence of carbon-rich domains [6]. These domains extended both along the c axis as well as in the 2D layers, and the density of carbon atoms in these domains exceeded 1018 cm−3 [6], as indicated by secondary-ion mass spectroscopy. The presence of carbon in hBN was revealed by direct imaging via annular dark-field electron microscopy [7] on samples exfoliated from bulk hBN

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