Identification of the Nitrogen Interstitial as Origin of the 3.1 eV Photoluminescence Band in Hexagonal Boron Nitride

TL;DR

This study identifies nitrogen interstitials as the origin of the 3.1 eV photoluminescence band in hexagonal boron nitride, using advanced hybrid functional calculations to match experimental observations.

Contribution

The paper introduces a new N$_i$ defect configuration with lower energy and deeper charge transition levels, explaining the PL band and ruling out nitrogen vacancies as the source.

Findings

N$_i$ acts as an efficient compensating center in n-type hBN.

Calculated PL at 3.0 eV matches the experimental 3.1 eV band.

Nitrogen vacancies are not responsible for the TBC EPR center.

Abstract

Nitrogen interstitials (N$_\mathrm{i}$) have the lowest formation energy among intrinsic defects of hexagonal boron nitride (hBN) under n-type and N-rich conditions. Using an optimized hybrid functional, which reproduces the gap and satisfies the generalized Koopmans condition, an N$_\mathrm{i}$ configuration is found which is lower in energy than the ones reported so far. The (0/-) charge transition level is also much deeper, so N$_\mathrm{i}$ acts as a very efficient compensating center in n-type samples. Its calculated photoluminescence (PL) at 3.0 eV agrees well with the position of an N-sensitive band measured at 3.1 eV. It has been also found that the nitrogen vacancy (V$_\mathrm{N}$) cannot be the origin of the three boron electron (TBC) electron paramagnetic resonance (EPR) center and in thermal equilibrium it cannot even exist in n-type samples.