Photoelectrochemical etching of highly doped n-type 4H SiC in dilute hydrofluoric acid along different crystallographic orientations under low voltage and/or low current conditions is studied. Scanning electron microscope images show that anodization of the hexagonal polytype 4H SiC with subsequent pore formation proceeds anisotropically. It is proposed that under uv illumination the crystallographic planes terminated with silicon atoms are more resistant to electrolytic attack than the planes terminated with carbon and mixed silicon-carbon atoms. This model is used to explain the observed triangular-channel pore morphologies. A clear indication was found that the resultant pore structure does not depend on the direction of the external electric field applied to the sample. Electrical parameters recorded as part of the photoelectrochemical etching process are described and interpreted.

We report the observation of a paramagnetic interface defect in thermally oxidized porous n-type doped 4H-SiC/SiO(2). Based on its axial symmetry and resolved hyperfine interactions it is attributed to an sp(3) carbon dangling bond center situated at the SiC side of the interface. This center is electrically active and pins the Fermi level in the oxidized samples. No silicon related paramagnetic dangling bond centers are observed. The formation of dangling bond centers seems to be related to interstitial oxygen diffusion at the interface during the oxidation process.

We have fabricated free-standing SiC nanoporous membranes in both p -type and n -type material. We showed that these membranes will permit the diffusion of proteins up to 29000 Daltons, while excluding larger proteins. By using radioactively labeled albumin, we also show that porous SiC has very low protein adsorption, comparable to the best commercially available polymer nanoporous membrane.

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Porous silicon carbide fabricated from p-type 4H and 6H SiC wafers by electrochemical etching in hydrofluoric electrolyte is studied. An investigation of the dependence on wafer polarity reveals that pore formation is favored on the C face while complete dissolution occurs on the Si face. When the etching is done on the C face, the pore wall thickness decreases with increasing current density. The morphology of the front surface of the sample depends on the prior treatment of the workpiece surface. The porosity is estimated based on the analysis of scanning electron microscope images, charge-transfer calculations, and gravimetric analysis.