Surface, pore morphology, and optical properties of porous 4H-SiC

Electron microscopy and spectroscopic ellipsometry are used to investigate the microstructural and optical properties of porous SiC. It is discussed that 1c dislocations are likely to play a role in the initial phases of the anodization process in terms of formation of nanometer sized holes. Pores are found to initially propagate nearly parallel with the sample surface and gradually change direction toward the c axis. Pore sizes are found to increase with depth toward the interface between the porous SiC and the substrate. A different pore morphology is found along the internal surfaces of micropipes, where structures are relatively large in size and appear spherical in shape. The anisotropy in pore propagation influences the etch rate, which varies in a nonlinear manner with the anodization time. The etching rate is also influenced by the larger absorptivity of the porous layers caused by formation of a disordered phase at the interface between the crystalline SiC and the pores. Ellipsometric analysis of porous SiC layers yields thicknesses and porosities in good agreement with the electron microscopy observations. Optical properties of the solid content of the porous layers are significantly different from those of bulk crystalline SiC, and depend on the etching time and sample thickness. (C) 2001 The Electrochemical Society.