Edge effect in electrochemical etching on porous silicon and its direct evidence on photoluminescence patterns

An edge effect caused by a spontaneous bias on the anodizing current density at the edged area is found during electrochemical etching. On the porous silicon films formed by the electrochemical etching method, evidence of the edge effect appearing on the photoluminescence pattern is first proposed in the study. With an appropriate electrolytic cell design where a halo baffle is placed between the anode and cathode as a barrier to reactant flux on the outer ring, the flux at the edge would be curved. It results in various degrees of electrochemical reactions and various porous structures on the silicon wafer. The experimental results propose an exhaustive view at the edge area in electrochemical etching process, and also propose an optional selection for free-mask patterning technology of porous silicon.