Anisotropic textured silicon obtained by stain-etching at low etching rates

The structure, luminescence and etching kinetics for porous silicon stain-etched at different temperatures are studied. The results reveal that for temperatures below 10 degrees C and for short etching times, a novel anisotropic structure based on surface roughness preferentially oriented in the (100) direction is observed. At temperatures higher than 10 degrees C or large etching times, typical macropores and mesopores with non-preferential pore wall orientation are detected. The luminescence spectra of the samples with preferential surface roughness orientation are red-shifted with respect to the samples with typical isotropic orientation. The results are interpreted in terms of average etching rates and pore growth.