Origin and roles of oxygen impurities in hexagonal boron nitride epilayers

Abstract

Photoluminescence emission spectroscopy and electrical transport measurements have been employed to study the origin and roles of oxygen impurities in hexagonal boron nitride (h-BN) epilayers grown on sapphire substrates. The temperature dependence of the electrical resistivity revealed the presence of a previously unnoticed impurity level of about 0.6 eV in h-BN epilayers grown at high temperatures. The results suggested that in addition to the common nitrogen vacancy (V N) shallow donors in h-BN, oxygen impurities diffused from sapphire substrates during high temperature growth also act as substitutional donors (O N). The presence of O N gives rise to an additional emission peak in the photoluminescence spectrum, corresponding to a donoracceptor pair recombination involving the O N donor and the C N (carbon occupying nitrogen site) deep level acceptor. Moreover, due to the presence of O N donors, the majority charge carrier type changed to electrons in epilayers grown at high temperatures, in contrast to typical h-BN epilayers which naturally exhibit "p-type" character. The results provided a more coherent picture for common impurities/defects in h-BN as well as a better understanding of the growth mediated impurities in h-BN epilayers, which will be helpful for finding possible ways to further improve the quality and purity of this emerging material.

Improvements in structural and optical properties of wafer-scale hexagonal boron nitride film by post-growth annealing

“…S4) are observed from the post-annealed h-BN film while no exciton-related peak is observed from the as-grown h-BN film that is attributed to the disordered h-BN structure quenching the excitonic PL 51–53 . The transition peaks related to a donor-acceptor pair (DAP) transition at 303.4 nm together with its replicas at 317 and 332.8 nm 54 , as well as the emission peaks at 226 and 232 nm originating from the excitons localized at certain structural defects 55 appear after the post-annealing. Although near band-edge phonon replicas of indirect exciton resulting in emission at wavelength shorter than 215 nm is not observed, we believe that remarkable enhanced PL enabled by improved crystallinity after the post-annealing can provide a great opportunity for use of the large-area, multi-wafer scale h-BN film grown by MOCVD as a highly efficient active material in optoelectronic applications.…”

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

“…The luminescence properties of hBN have been studied mainly in recent years. [ 7,9–15 ] Museur et al reported three photoluminescence (PL) bands at the energies of 5.3, 3.75, and 3.1 eV for pyrolytic hBN (pBN) samples. [ 9 ] pBN samples are high‐purity samples, free of carbon and oxygen.…”

Far-UV photoluminescence microscope for impurity domain in hexagonal-boron-nitride single crystals by high-pressure, high-temperature synthesis

“…In contrast, the impure sample, which contains a subtle amount of carbon and oxygen, 5 shows additional luminescent structures in the region between 300 and 400 nm (the origin of which is still controversial. 5,[8][9][10][11][12][13] ) Moreover, owing to the relaxation process of excited carriers through excitons to the impurity bands, the intensity of the exciton luminescence for the impure sample is lower than that for the pure sample. 14 In fact, such an impurity-incorporated domain is often contained in HPHT single crystals.…”