Lublow, M. ; Lewerenz, H.J.: Fractal photocorrosion of silicon electrodes in concentrated ammonium fluoride. Electrochemical and Solid-State Letters 10 (2007), p. C51-C55
DOI version (server of publisher)
Silicon photoelectrodes, immersed in 40% NH4F electrolyte, exhibit large-scale fractal etch patterns at anodic potentials near 6V. Depending upon light intensity and doping, three regimes were identified, characterized by: i) etch groove ramification; ii) surface-lattice symmetry; iii) chaotic corrosion. The pattern formation in regimes i/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.