Luminescence centers in cubic boron nitride

Abstract

Complex and multiband photoluminescence spectra for GB and HBN centers in single crystals of cubic boron nitride (cBN) were recorded in the wavelength ranges 385-400 nm and 365-395 nm and the nature of these centers was studied. The use of models involving resonance vibrations and strongly shifted configuration diagrams for the electronic ground state and excited state made it possible to associate formation of the GB-1 center with the presence of tungsten impurity in cBN. It was established that the HBN band in the 300-350 nm range of the cathodoluminescence spectra of cBN polycrystals, single crystals, and micropowders is associated with luminescence centers present in microinclusions of graphite-like boron nitride (hBN). The nature of the hBN band is tentatively interpreted within the model of recombination of donor and acceptor defects in hBN: respectively nitrogen vacancies and carbon atoms in positions substituting for nitrogen.Key words: cubic boron nitride, photoluminescence, cathodoluminescence, nature of optically active defects, luminescence center, spectrum with complex structure, resonance vibrations, configuration diagram.Introduction. Cubic boron nitride (cBN), as a wide-gap semiconductor, is a promising material for use in electronics and optoelectronics, detectors and devices suitable for operation under high radiation and temperature conditions and also in chemically aggressive media. Since the defect and impurity structure of cBN has not been well studied, it should be quite effective to analyze it by luminescence correlated with the macroscopic characteristics of the material, taking into account the indicated practical applications.From the standpoint of basic research on cBN, of course, direct analysis of the nature of the optical transitions at the luminescence centers in cBN is of interest, including comparison with its closest Group III-Group V analogs: diamond and gallium nitride.Thus in the luminescence spectra of gallium nitride, we observe a sufficient number of features of a type associated with donor-acceptor recombination or with recombination on free or bound excitons [1]. Of course, in the indicated cases, oppositely charged impurities or defects are present simultaneously in GaN which are introduced into the material by doping or are present in the material as intrinsic defects. Effective doping of diamond is difficult, and obtaining diamond with n-type conductivity is problematic. This is explained by the lack of luminescence centers of the above-indicated type in diamond [2] and formation of many defects in diamond such that electronic transitions in them are intracenter transitions.The number of luminescence centers in cBN that have been detected so far is small compared with diamond and GaN, and only isolated centers have been thoroughly studied. Based on the hypothetical nature of the optical transitions at these centers, the overall results of luminescent studies of cBN show considerable similarity to diamond. Thus in the luminescence spectra of cBN, the predominant bands...

Formation of flower-like MgO crystal and its effect on the photoluminescence of Mg-cBN ceramics

“…5(a) was interpreted hypothetically within the model of recombination on donor and acceptor defects in hBN by Shishonok [41]. Their presence in the luminescence spectra of annealed cBN ceramics suggested a phase inhomogeneity, i.e., the presence of microinclusions of hBN in the annealed samples, as detected by XRD measurements (see Fig.…”

“…We have found this assumption to be reasonable to justify that replicas of the main band in the spectrum recorded at intervals equal to the energy of the LO phonon of the hBN crystal lattice. Meanwhile, considering the HBN center in cBN [41], the electronic transitions at the HBN center can occur upon interaction with the phonon with energy ∼65 meV. The phonon with energy of 64 meV in cBN is localized on a nitrogen vacancy.…”

Room-temperature single photon emitters in cubic boron nitride nanocrystals

“…The majority of the ZPLs arising from single defects, however, are found to share similar spectral response, as can be observed by comparing Fig 2 (b) and Fig 2 (c), some of which resemble features previously reported from color centers in cBN, e.g., under UV-excitation. 4 Other ZPLs tend to resemble those observed in hBN defects (Fig 2 (d)), e.g., with phonon replicas matching the E2g phonon mode energy (~165 meV). Thus, it is noted that both cBN and hBN defects are found across the sample.…”

“…Despite the inhomogeneity in the spatial distribution of flakes owing to the dropcasting technique, a collection of isolated bright spots across large sample areas is systematically observed upon sub-bandgap excitation (Fig 2 , some of which resemble features previously reported from color centers in cBN, e.g., under UV-excitation. 4 Other ZPLs tend to resemble those observed in hBN defects (Fig 2 (d)), e.g., with phonon replicas matching the E2g phonon mode energy (~165 meV). Thus, it is noted that both cBN and hBN defects are found across the sample.…”

“…13, 14 Here, we report on room-temperature single-photon emission (SPE) originating from atomic defects in cBN, some of which show spectral features like those previously reported for color centers in single-crystal cBN. 1,4 We overcome some of the aforementioned limitations by using nanocrystalline cBN flakes, which have a high density of near-surface atomic defects accessible through optical laser excitation. By employing confocal Raman spectroscopy, we show that the optical regions of interest are indeed dominated by the cubic phase of BN, while small hexagonal boron nitride (hBN) quantities arising as a synthesis byproduct are found to phasesegregate in nm-sized regions.…”