Optical property and picosecond response of porous silicon wafer

Optical quality, free standing and highly photoluminescent PSi was prepared from both, p- and n-type Si wafers using electrochemical anodization of c-Si. The porosity and the final structural and optical properties of the samples were found to be altered drastically by changing the acid concentration, current density, anodization time as well as the characteristics of the Si-wafer. In optical measurement, a broad and intense absorption band is in the UV-Visible region with a cut-off edge at ∼400 nm. A strong red emission was found to be at ∼670 nm. It is extremely broad even at 8 K. The experimental results show that a group of sites can be simultaneously excited by pump laser due to excitation energy coincidence. In nonlinear optical measurement the optical response was characterized using degenerate four-wave-mixing (DFWM) in a backward configuration. The response signal consists of an instantaneous component followed by a long lived, slowly decaying component. They are associated with the third-order s...