Optical properties of porous silicon coated with ultrathin gold film by RF-magnetron sputtering

Optical properties of porous silicon (PS) with ultrathin gold (Au) coatings were investigated. The gold films were deposited by using an RF-sputter-deposition technique on PS prepared by electrochemical anodization of P-type (1 0 0) Si. Photoluminescence (PL) spectroscopy and UV/VIS photospectroscopy analyses were performed to investigate the PL and optical transmittance properties of the Au-coated PS samples. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron emission spectroscopy (XPS) analyses were also performed to investigate the origin of the PL enhancement by Au deposition. The PL intensity of PS is 6.4% increased by depositing 5.3 nm Au film using an RF-sputtering technique, but it is decreased 28.4% by postannealing. FTIR, spectrophotometry and XPS analysis results suggest that the PL enhancement by Au film deposition is attributed to the oxidation inhibiting effect of the Au film. However, it is not desirable to deposit an Au film thicker than 5.3 nm on PS as the PL intensity is decreased rather than increased owing to a significant decrease in the transmittance. Deterioration in the PL of the Au-coated PS by postannealing is ascribed to oxidation of the PS layer occurring at the high annealing temperature in spite of the Au passivation.