The thermoluminescence (TL), phosphorescence and cryoluminescence of n-type hexagonal (6H) SiC crystals

The low temperature (down to liquid helium temperature) TL, phosphorescence and cryoluminescence of n-type 6H SiC crystals is described. The crystals contained nitrogen as the major impurity at concentrations of about 10¹⁶ cm^-3. The glow curves exhibited peaks at about 25, 45, 70 and 90°K (in addition to a peak at 250°K). Thermal activation energies for the above peaks ranged between 0.02 and 0.14 eV (0.30 eV for the 250°K peak). These are much lower than energies reported earlier for nitrogen donor levels in 6H SiC. The values obtained for the 70–90°K peaks (0.08–0.14 eV) fit quite well those obtained by electrical transport measurements and Raman scattering.The crystals exhibited strong phosphorescence even at liquid helium temperature. This was shown to be only partly due to thermal release from traps, the other components being due to pair-recombination and optical release from the shallow traps by the black body radiation (BBR) from the walls of the cryostat. This BBR was found to be responsible also for the observed cryoluminescence.