Structural, electrical, and optical properties of 4$H$-SiC for ultraviolet photodetectors

The results of investigations of initial $n$-4$H$-SiC structures by various methods are presented. The structures represent a highly doped $n^+$ substrate with epitaxial layers 5 $\mu$m thick grown by chemical vapor deposition (CVD). The concentration of uncompensated donors in the epitaxial layer is in the range of $N_d-N_a$ = (1–50) $\times$ 10$^{14}$ cm$^{-3}$. Using the results of X-ray diffraction analysis, it is found that, in order to obtain efficient 4$H$-SiC ultraviolet photodetectors, it is desirable to have structures of epitaxial layers in which the effect of point-defect gettering, leading to an increase in the lifetime of charge carriers and in the values of quantum efficiency, is observed. The photosensitivity of the investigated samples significantly depends on the degree of imperfection of the CVD epitaxial layer, which results in a change in the lifetime of charge carriers and, as a consequence, in a change in the quantum efficiency of 4$H$-SiC ultraviolet photodetectors.