Synthesis and fluorescence properties of columnar porous silicon: the influence of Cu-coating on the photoluminescence behaviour of hydrofluoric-acid-treated aged columnar porous silicon†
A column-shaped porous silicon (PSi) sample was successfully prepared by electrochemical anodization in a hydrofluoric acid (HF) containing electrolyte. The PSi exhibited an unstable red photoluminescence (PL). The PL arose from surface oxygen defects under quantum confinement effects and degraded as the exposure time in air increased. After hydrofluoric acid treatment and 2 min Cu sputtering coating, the PL-degraded aged column-shaped PSi showed dual PL bands in the blue and yellow ranges. Cu-coated fresh PSi without aging and Cu-coated aged PSi without HF treatment did not show this result. The PL intensity of these two bands was greater than that of the fresh column-shaped PSi. These two emissions also showed relatively good stability, as determined from the fact that they had the same intensities after air treatment for three months. The improvement of PL can be attributed to the surface unstable SiO that combines with the sputtered Cu, forming new Cu related defect sites and surface nanostructures. The method in this study does not require any heating treatment, because SiO is very unstable, particularly in a high-moisture environment.