LARGE PRESSURE EFFECT ON PHOTOLUMINESCENCE LINES IN 6H SIC-TI CRYSTAL

The effect of hydrostatic pressure up to 7.5 kbar on the so-called ABC lines in the photoluminescence spectrum of hexagonal 6H SiC crystals with traces of Ti atoms has been studied at 77 K. Linear pressure shifts of these lines were found to be rather large (1.08-1.25 meV kbar(-1)) considering low compressibility of the crystal and the expected very small pressure coefficient for the band gap in 6H SiC. The recorded pressure shifts exceed by more than 10 times those of the well-known R luminescence lines in ruby, Al2O3:Cr3+, which has roughly the same compressibility as SiC. Fairly high sensitivity of ABC lines to the applied pressure is interpreted in terms of a ligand field model for a quasimolecular impurity centre where Ti atom substitutes an about 20% smaller Si atom in SiC crystal.