Exciton line temperature evolution in 4H-SiC crystals

A complete study of the free and bound exciton photoluminescence (PL) line temperature behavior on high-quality 4H-SiC epitaxial crystals is presented. At low temperatures (T < 60 K), in the PL spectra the lines related to both free exciton (FE) and nitrogen-bound exciton (N-BE) are visible. At higher temperatures are present exclusively FE emission lines; their intensity decreases as the sample temperature increases, and they are no longer visible at about 140 K. The FE and N-BE temperature behavior is studied and the activation energies of the phenomena (growth and quenching) associated with the low-temperature photoluminescence (LTPL) lines are determined. Some possible interpretations of the obtained values are proposed, and a kinetic model describing the recombination processes that produce luminescence lines is suggested.