hBN Crystals Research Articles

The optical absorption and photoconductivity spectra of hexagonal boron nitride single crystals

AbstractRecently, a strong cathodoluminescence at 215 nm (photon energy 5.765 eV) has been reported on pure HPHT hexagonal boron nitride (hBN) single crystals (K. Watanabe et al., Nature Mater. 3, 404 (2004)). For the first time, we measured the photocurrent and optical absorption spectra of these new hBN crystals in a broad spectral range 1–6.6 eV. Our measurements support the previously published results, especially that the single crystal hBN has a direct band gap about 5.95 eV, and a rather strong exciton binding energy that allows excitons to exist even at room temperature. We found three new opto‐electronic transitions at 2.7, 3.6 and 5.4 eV and observed the oscillatory photoconductivity in 2.7–3.6 eV region. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Precipitation mechanism of BN in the ternary system of B-Mg-N

The phase relations in the ternary system B-Mg-N resulting from the reaction between Mg and BN at 2.5 GPa were investigated by means ofin situ differential thermal analysis (DTA) supported by a conventional quenching technique. One compound, Mg3B2N4, was newly formed when melted Mg reacted with hexagonal BN (hBN) solid above 1150° C and formed the eutectic with Mg and hBNat 737 and 1295° C, respectively. It was also confirmed that hBN crystals were precipitated from the liquid above 1300° C. The catalytic mechanism controlling cBN formation in the system Mg-BN was discussed from the experimental results of the present work. The lower temperature limit of cubic BN (cBN) growth region appears to be closely related to the initial formation of liquid phase due to a eutectic of Mg3B2N4-BN.