Stain etching of silicon with V2O5

Formation of porous silicon by etching of silicon with vanadium pentoxide dissolved in HF(aq) has been studied with infrared spectroscopy and electron microscopy. The rate of film growth depends strongly on the V2O5 concentration. Addition of ethanol greatly decreases the etch rate and changes the pore morphology from a mixture of {100} + {110} planes to predominantly {100} planes. A plot of thickness vs. etch time in aqueous solutions evolves from a quadratic to a linear dependence. A model is developed in which the surface area depends linearly on film thickness and the thickness exhibits the measured functional form with respect to time. In this model pores with a uniform diameter nucleate randomly, initially grow rapidly before slowing to grow at a constant rate. The pore density increases linearly with time then saturates causing the transition to the linear growth rate phase. This model simultaneously fits both the short time and long time behaviour of the thickness and surface area. Pore formation does not involve an oxide intermediate. Films emit brilliant visible photoluminescence, and are highly uniform both in structure and photoluminescence. [GRAPHICS] Photographs of a porous Si sample etched in V2O5+HF taken when the sample is illuminated with white light (left) or UV light (right), which excites uniform yellow photoluminescence. "75E" was scratched into upper left corner for identification before etching. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim