Characterization of silicon carbide epitaxial filmd by differential reflectance spectroscopy

摘要

We are presenting a simple non-destructive method for characterising SiC samples (Lely-crystals, CREE-substrates, and epitaxial films). With our method we observed ultraviolet differential reflection spectra of SiC samples and compared with pare Lely-crystal to estimate their structural quality. Our optical differential method is based on the experimental fact that doping of a crystal leads to appreciable changes of the optical fundamental absorption spectrum, which we interpreted as a uniform broadening and a shift of differential spectra. The broadening of absorption peaks can be caused not only by doping, but also by any defects of the crystal lattice (neutral impurities, clusters, micro-pipes and others), that destroy its periodicity. The shifts of these peaks inform us about the free carrier concentration. The experiment has shown we can detect minimum free carriers concentration up to n{sub}(min)= (N{sub}D-N{sub}A) = 6.10{sup}15 cm{sup}-3. Besides we can detect minimum frequency of impacts with lattice defects as V{sub}(min) = 3.10{sup}12 s{sup}-1 Converting to charged centres concentration it equals (N{sub}D+N{sub}A) = 5.10{sup}16 cm{sup}-3. Considering the Small depth of light probe (less than 0.1μm) and delicacy of thin films, our contactless method is mostly applicable for its testing.