Raman study of color-zoning cubic boron nitride single crystals

Unintentionally doped cubic boron nitride (cBN) single crystals with color zoning were investigated by Raman spectroscopy. Besides the TO mode at 1053 cm−1 and the LO mode at 1304 cm−1, some little vibrational bands at 925 cm−1, 955 cm−1and 1247 cm−1 corresponding to the amber regions in the {1¯1¯1¯}N sectors of cBN crystals were observed. These vibrational bands probably result from the disorder-activated Raman scattering (DARS) due to the high defect densities. It is shown that these defects and impurities are nonuniform, easily formed and incorporated in {1¯1¯1¯}N growth sectors during the growth process of cBN crystals. These defects and impurities are color centers in cBN, therefore, the cBN crystal exhibits symmetrical color zoning relative to the {111} growth sectors.