Raman scattering of light in doped cubic boron nitride

Abstract

535.375:548The Raman spectra of single crystals of cubic boron nitride (cBN) doped with beryllium and also synthesized in the absence of dopants are investigated. It is shown that the wide bands at 215 and 535 cm −1 can be registered in the Raman spectra of the (1 _ 1 _ 1 _ ) faces of undoped cBN crystals and that the Be impurity penetrates into the cBN crystals predominantly in the direction of these faces. In the spectra of the investigated cBN samples doped with Be, the contour of the TO and LO phonon lines does not take the Fano shape, in contrast to diamond, which can point to an insufficient concentration of the dopant for attaining the Fano interference or to the absence of it in cBN. The wide bands have been investigated on the assumption that they are "boson"-like and result from small-size disorders in both undoped and doped cBN samples with the sp 3 bond deformed by Be.Keywords: Raman scattering, cubic boron nitride, beryllium, wide band, Fano profile, "boson"-like peak.Introduction. Cubic boron nitride (cBN) is the most wide-band semiconductor of those known and the nearest analog of diamond, surpassing the latter in its thermal, radiative, and chemical stability. In contrast to diamond, cBN can be doped with dopants of n and p types. Cubic boron nitride is of fundamental and practical interest as a material to be used in optoelectronics, electrons-emitting devices, and also for fabricating sensors operating in aggressive media and at high temperatures. The problem of introduction of a controlled impurity into cBN is urgent for this compound to be used in the practical applications named.Beryllium is used rather effectively for doping semiconductors and acts as an acceptor in Ge, Si, GaN, and SiC [1-4].Beryllium-doped cBN was synthesized [5,6] in the form of powders, single crystals, and polycrystals. Its electrophysical properties (volt-ampere-and C-V characteristics, Hall effect) were investigated. It has been established that in cubic boron nitride with different contents of impurity beryllium forms an acceptor level in the 0.25-1.03-eV region. In the EPR spectra of powders of cBN doped with Be a hyperfine structure was revealed in the form of a septet of lines with central signal with g = 2.0016. It is well known that the hyperfine structure mentioned may result from the interaction of unpaired s-electrons with the nucleus the spin of which is equal to 3/2. The nature of the observed paramagnetic defect is directly associated with an admixture of beryllium, since the spin of the Be atom nucleus is 3/2 [7].A number of works are now available in which an attempt was made to theoretically calculate the energy states of various defects in cBN, including vacancies, interstitial atoms, and some impurities, including beryllium [8][9][10][11][12][13][14].The Raman method used for identifying one phase of a substance or another and the quality of crystals is an effective method of studying stresses and the concentration of free carriers in them.At the present time, a vast amount of information has been obt...

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

“…Extensive studies have been conducted on the optical properties of large cBN single crystals by means of photoluminescence [12,13], catholuminescence [14][15][16], and Raman spectrum [13,[17][18][19]. As compared to large cBN single crystals, cBN compacts and ceramics, comprised of a plurality of cBN crystals properly bonded together with or with- * Corresponding author.…”

“…Recently, in a number of studies [20][21][22][23][24][25][26], some attempts have been made to investigate the luminescent properties of cBN ceramics and compacts doped or activated by rare earth elements, in order to develop visible light emitters and phosphors that can withstand extreme environmental conditions. It is known that beryllium is an effective p-type dopant for poly and single cBN crystals [19], however, there is a considerable safety issue due to its high toxicity and fast oxidation. To explore the potential direct doping of cBN ceramics using Mg as a possible substitute of beryllium, cBN ceramics with addition of Mg were sintered under high temperature and high pressure conditions, followed by post-annealing treatment.…”