UD-3 defect in4H,6H,and15RSiC: Electronic structure and phonon coupling

Abstract

The UD-3 photoluminescence (PL) spectrum is observed in high-resistive or semi-insulating bulk $4H,$ $6H,$ and $15R$ SiC. It consists of one no-phonon (NP) line in $4H$ and $6H$ SiC and two NP lines in 15R SiC. The line positions are 1.3555 eV in $4H$ SiC, 1.3440 eV in $6H$ SiC and 1.3474 eV $\left(\mathrm{UD}{-3\mathrm{}}_{\mathrm{L}}\right)$ and 1.3510 eV $\left(\mathrm{UD}{-3\mathrm{}}_{\mathrm{H}}\right)$ in 15R SiC. In PL excitation experiments, an additional set of four lines $\left({\mathrm{U}\mathrm{D}-3\mathrm{}}^{\mathrm{I}}{–\mathrm{U}\mathrm{D}-3\mathrm{}}^{\mathrm{IV}}\right)$ is observed in all three polytypes. The symmetry of the ground state and the excited states involved in these transitions is determined from Zeeman and polarization experiments. The NP line is accompanied by a broad phonon assisted side band. In addition, three sharp transitions $\mathrm{UD}{-3\mathrm{}}^{\mathrm{a}},$ $\mathrm{UD}{-3\mathrm{}}^{\mathrm{b}},$ and $\mathrm{UD}{-3\mathrm{}}^{\mathrm{c}}$ and three broader features have been observed. These are assigned to local phonons.