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, and the luminescent nature of the PS layer was also studied qualitatively. A layered pore structure developed after about 300 s of anodization, and pore morphology became simpler with increasing thickness of the PS layer. All luminescent PS layers were found to show spongelike structure 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-type PS. No systemic tendency of the lattice expansion was seen under various forming current densities. Luminescent PS layers showed slightly broader background intensity than nonluminescent ones. It was also shown that the anodization of the PS layer took place through two anodization processes: primary and secondary anodizations; secondary anodization was effective in forming luminescent parts having spongelike structure.