Laser spin-flip scattering from excitons in SiC

High densities of photoexcited excitons have been produced in Al-doped, $6H$ polytype silicon carbide via krypton-laser illumination. Raman spin flip of the electrons in these excitons has been observed, i.e., transitions from the ${\Gamma }_6$ to ${\Gamma }_5$ exciton levels in magnetic fields from zero to 14 tesla. Three transitions are tentatively assigned to excitons at Ti isoelectronic traps and satisfy the predicted dependence $\hslash \omega \mathrm{}\left(H\right)={[{\Delta }_0^2+{\left({\mu }_B{g}_{e}H\right)}^2]}^{\frac{1}{2}}$. The parameters determined are: exchange energies ${\Delta }_0=1.12, 1.32, \mathrm{and} 1.50$ meV, and electron gyromagnetic ratio $g_e=1.97\mathrm{}$; these values agree superbly with the value ${\Delta }_0=1.1\mathrm{}$ meV identified by van Kemenade and Hagen as the exchange energy for excitons bound to ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$ isoelectronic traps (the dominant naturally occurring isotope) in $6H$ SiC, and with $g_e=1.96\mathrm{}$ from Hartman and Dean's study of SiC:N, and $g_e=2.00\mathrm{}$ from electron-paramagnetic-resonance studies of $6H$ SiC by Balona and Loubser. Extremely intense anti-Stokes (up-converted) luminescence associated with the Al acceptors in the present work yields a value of 0.27 eV for the Al binding energy, in agreement with earlier studies.