Growth, Luminescence, Selection Rules, and Lattice Sums of SiC with Wurtzite Structure

Abstract

Relatively large and pure crystals of the rare $2H$ polytype of SiC (wurtzite structure) have been grown, using the method of Adamsky and Merz, with special attention to purity. Absorption and luminescence measurements (2 to 8°K) show that $2H \mathrm{SiC}$ has an indirect energy gap of 3.330 eV, the largest yet reported for a SiC polytype. The polarized luminescence was analyzed, using group-theoretical selection rules to determine the active phonons, as Lax and Hopfield did for Ge and Si. The observed spectrum is consistent with the selection rules, provided there are conduction-band minima at the $K$ positions of the Brillouin zone (two minima). Certain "forbidden" lines are found to be temperature-dependent, as a similar line is in Ge. It is proposed to extend to all SiC polytypes the lattice sum rule discussed by Brout and by Rosenstock. The $2H$ lattice sum at $K$ is found to be within 2% of the cubic SiC lattice sum at $X$, even though the phonon energies measured in the luminescence spectra are quite different. As far as "trace variable" forces are concerned, SiC resembles C (diamond) more than it does Si.