Morphological properties of porous-Si layers for n(+)-emitter applications

Porous silicon layers prepared on n(+) emitters are investigated by a combi nation of spectroscopic ellipsometry, transmission electron microscopy and sheet resistance measurements. The porous silicon is formed by an anodic su rface treatment of uniformly doped emitters prepared by chemical vapour dep osition and of diffused emitters. The results show a good correspondence be tween the thicknesses obtained with the different techniques. The porosity of the layers increases for increasing doping level and saturates at a dopi ng above similar to 5x10(19)/cm(3). The formation rate shows an inverse dop ing dependence. The top surface layer of the porous silicon is in all cases more dense than the bulk, which is related to an initially faster formatio n rate. (C) 1999 Elsevier Science B.V. All rights reserved.