TEM AND CATHODOLUMINESCENCE STUDIES OF POROUS SIC

The structure of porous silicon carbide has been studied using transmi ssion electron microscopy both in planar geometry and in a cross-secti on of a porous film. Peculiar structures in the form of shared rosette s with petals of about 3-8 mu m in size and a density of 6 x 10(3) cm( -2) were found in the subsurface layer. These formations are pierced b y thin channels (pores) with an average diameter of 10 nm, Near the su rface of the layer the channels in the 'lobes' may be directed at smal l angles to the surface, but, with increasing depth, ail of them becom e approximately perpendicular to the surface, with branching observed. On channel walls there is a rather thick layer of fine particles with characteristic dimensions of the order of 0.8-1.0 nm. Spectral cathod oluminescence studies have been performed with luminescence excited by a narrow (2 mu m) electron probe on parts of the initial sample and p orous film having varied thickness (0.03-3 mu m). A layered structure was revealed in the porous film, with the layer responsible for the 'b lue' luminescence band (hv(max) = 2.65 eV) due to the presence of fine crystallites located at a certain depth, rather than immediately near the surface.