Luminescence of4HSiC, and Location of Conduction-Band Minima in SiC Polytypes

Abstract

The low-temperature luminescence of Lampert complexes in $4H$ SiC is reported. Simultaneous photon and phonon emission gives rise to spectra from which it is possible to obtain 18 phonon energies. The interpretation of the phonon spectrum suggests positions of low symmetry for the conduction-band minima, requiring a 12-valley model for electrons. Suitable positions of low symmetry can be found by noting the planes of energy discontinuity within a large zone (equivalent to four Brillouin zones), and by a comparison with cubic SiC. The method can be extended to other SiC polytypes, and may provide a unifying principle for locating the conduction-band minima. It explains the similarities already observed in the phonon spectra of seven polytypes.