Optical Properties of21RSiC: Absorption and Luminescence

Abstract

Measurements from 4.2 to 300°K show that the absorption edge of $21R$ SiC is due to phonon-assisted transitions which create excitons. The exciton energy gap is 2.853 eV at 4.2°K. A region of anomalous absorption is found. The luminescence at 6°K is due to excitons bound to nitrogen atoms (Lampert complexes). The binding energies, measured for six of the seven inequivalent nitrogen atoms, range from 10 to 40 meV. Applicability of the Haynes rule is discussed. A number of phonon energies are obtained from the luminescence spectrum, which is simpler than expected for a high polytype. Comparisons with other SiC polytypes are given throughout.