Structural analysis of porous silicon multilayer using X-ray diffraction

A porous silicon monolayer (PSL) and four types of porous silicon multilayers (PSMLs) with 2-, 3-, 7-, and 50-layers were studied using the X-ray double crystal method. PSMLs were formed by controlling the anodization current density. Only three distinct peaks were observed in each rocking curve for these PSMLs, which showed two kinds of porous silicon layers with good crystallinity. It was also shown that the PSL and PSMLs were slightly different in the state of lattice strain. To observe the structure and depth-distribution of lattice strain of PSMLs, a new X-ray cross-sectional topographic technique (XCST) has been proposed. Applying XCST to a three-layer porous silicon consisting of 5 mu m, 10 mu m, and 5 mu m layer thicknesses resulted in a clear x-ray cross-sectional topograph. From the topograph and the corresponding rocking curves, the precise distribution of the lattice strain was revealed. The XCST is useful for evaluating not only the PSML, but also general crystal multilayer structures such as superlattice hetero structures.