Characterization of porous silicon for solar cell application by atomic force microscopy

The anodically etched macroporous and nanoporuos silicon layers (PS) were tested in order to determine their surface roughness dependence on fabrication method. Porous silicon layers were obtained by electrochemical etching of n-type wafers, and then highly doped. Deep p(+) layers were prepared by boron diffusion into the PS from spin-on glasses. The structure of PS surface of solar cells obtained was examined by atomic force microscopy. The system of PS coated with nanoporous PS as a antireflection coating exhibited a uniform macroarray of regular square and faceted large features of various sizes as a texturisated solar cell with average 1.43 mu m high and computed roughness parameter R-z - 2.37 mu m. For the same macroporous silicon sample without additional nanoporous silicon layer computed R-z was 4.84 mu m. This could be explained by electropolishing of macroporous silicon surface. The obtained results confirm that AFM can be employed for the accurate measurement of the shape of macroporous silicon covered by the nanoporous silicon layer.