We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulating 4H-SiC material. Data from as-received samples show a monotonic decrease in α with incident energy density, with a pronounced change in slope at around 10 mJ cm-2. Annealed samples, on the other hand, exhibit an experimental trend of increasing α with intensity. Qualitative explanation of the observed behavior is presented that probes the possible role of spontaneous and stimulated emission for as-received samples. With annealing, trap related recombination is strongly reduced leading to higher carrier densities and increased free-carrier absorption with incident intensity. The role of band-filling and permittivity changes are shown to be inconsequential, while changes in internal fields could contribute to decreases in absorption.
- intensity dependence
- photoconductive switch