MICROSTRUCTURE AND CRYSTALLINITY OF N-TYPE POROUS SILICON

Microstructure and crystallinity of a porous silicon (PS) layer formed on a highly doped n-type silicon substrate were examined in detail, a nd the luminescent nature of the PS layer was also studied qualitative ly. A layered pore structure developed after about 300 s of anodizatio n, and pore morphology became simpler with increasing thickness of the PS layer. All luminescent PS layers were found to show spongelike str ucture near the surface. From the peak width of X-ray rocking curves, the crystallinity of n-type PS was found to be inferior to that of p-t ype PS. No systemic tendency of tile lattice expansion was seen under various forming current densities. Luminescent PS layers showed slight ly broader background intensity than nonluminescent ones. It was also shown that the anodization of the PS layer took place through two anod ization processes: primary and secondary anodizations; secondary anodi zation was effective in forming luminescent parts having spongelike st ructure.