s Recycling of Silicon Sludge and its Optical Properties

We have developed a mass production process of Si quantum dots using photo-induced chemical etching method with oxidation and etching agents and have investigated its optical properties. Average size of the fabricated Si quantum dots was estimated to be 2 nm. Absorption peaks of the fabricated quantum dots were observed in the short wavelength regions, e.g., 200 - 350 nm. On the other hand, in the case of raw sludge, absorption was not observed in the UV-visible wavelength regions due to the narrow energy band gap (e.g., 1.12 eV). The calculated energy band gap of fabricated Si quantum dots was calculated to be 3.5 eV by the modified Kubelka- Munk function. Blue emission peaks around 475 nm wavelengths were observed due to the quantum confinement effect. When the emission peak was fixed, two excitation peaks were observed in 340 nm and 380 nm, respectively, which seemed to be due to the energy band gap widening and/or surface coating with an ultrathin layer.