Photoluminescence in porous silicon obtained by hydrothermal etching

We have prepared porous silicon (PS) by hydrothermal treatment of silicon in a LiF-containing nitric acid solution. It does not utilize anodic etching. Scanning tunneling microscope (STM) studies show that the PS layers are uniform and consist of columns having cross sectional diameters of significantly less than 10 nm. Luminescence measurement results reveal that the wavelength of the photoluminescence (PL) peaks at 690 nm, which is somewhat shifted toward the higher energy compared to porous silicon obtained by anodic etching. A blue band around 430 nm together with an ultraviolet component peak at 370 nm appear after rapid thermal oxidation (RTO) of the hydrothermal etched sample in air at certain temperatures (650-1200 degrees C) for 30 s. Our results are interpreted in the light of the presently suggested theories.