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

Abstract

Nitrogen interstitials ((Formula presented.)) 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 Koopman's condition, an (Formula presented.) configuration is found, which is lower in energy than the ones reported so far. The (0/–) charge transition level is also much deeper, so (Formula presented.) 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 is also found that the nitrogen vacancy ((Formula presented.)) cannot be the origin of the three-boron-center (TBC) electron paramagnetic resonance (EPR) center and in thermal equilibrium it is even unlikely to exist in n-type samples.