Fractal photocorrosion of silicon electrodes in concentrated ammonium fluoride

Abstract

Silicon photoelectrodes, immersed in 40% NH4 F electrolyte, exhibit large-scale fractal etch patterns at anodic potentials near 6 V. Depending upon light intensity and doping, three regimes were identified, characterized by (i) etch-groove ramification, (ii) surface-lattice symmetry, and (iii) chaotic corrosion. The pattern formation in regimes i and ii reflects the underlying crystallographic structure: surfaces with (111), (110), (100), and (113) orientation are distinguishable on a micrometer scale. High spatial contrast in self-organized periodic etch topographies could be achieved on n-Si(111) for increased light intensities. In model considerations, correspondence to vertical pore formation on n-type silicon under back-side illumination can be stated. © 2007 The Electrochemical Society.