Stacked Layers of Different Porosity in 4H SiC Substrates Applying a Photoelectrochemical Approach

Abstract

Porous 4H-SiC layers were prepared from monocrystalline samples applying photo-electrochemical etching in hydrofluoric acid. The influence of both current and voltage controlled mode during photo-electrochemical porosification was investigated. It was found that the resulting degree of porosity, the homogeneity in porosity as well as the pore morphology mainly depend on the applied voltage, whereas the current level has an almost negligible impact on these important parameters. Based on these results, it is proposed that the formation of porous SiC during photo-electrochemical etching can be described by fractal growth. Finally the gathered knowledge allowed to detach the porous 4H-SiC layers, which comprised several sub-layers of alternating degree of porosity, from the 4H-SiC substrate. Such layers of tailored porosity are key components for several advanced device concepts such as optical filters or membranes for biological applications.