Boron-related luminescence in SiC

We report a photoluminescence (PL) study for both 4 H and 6H-SiC epilayers on boron-related recombination. The PL is not observed from as-grown epilayers, but after secondary ion mass spectrometry. In 4H the no-phonon (NP) line spectrum is near 3838 A, whereas it is located close to 4182 A in the 6H. The two spectra have almost the same phonon structure with localized modes. The luminescence is predominantly polarized perpendicular to the c-axis. The temperature dependence shows that the NP lines have at least three excited states higher in energy with energy separation depending on the polytype. The luminescence is quenched at T>70 K with a thermalization energy of about 40 meV. The absence of splitting or shift of the lines originating from excited states under applied magnetic field shows that the excited states have singlet character, whereas splitting is observed for the low-temperature NP lines. The luminescence of the NP lines in these samples is shown to increase with excitation time