Strong luminescence and easy color control for SiO_x thin films by using RF magnetron sputtering

Silicon-rich silicon-oxide (SRSO) films were deposited at room temperature by using an RF magnetron sputtering method. The optical properties and the chemical state of these films were characterized by using photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). We obtained light emissions of blue, yellow and red colors in the PL spectra by adjusting the power of the RF-generated plasma. Annealing the films at 1000 °C for 5 min, 10 min and 30 min, respectively, in an ultra-high-vacuum (UHV) chamber, we observed that the PL intensity was enhanced by 6 to 40 times that of the as-deposited sample. We also measured the core-level spectra of the related elements by using X-ray photoelectron spectroscopy (XPS). Investigating the chemical state change of the silicon 2p core-level, we found that the color variation and the light emission efficiency of the SRSO materials were strongly affected by the oxygen content embedded in the deposited films. This means that the PL wavelength of the SRSO films can be readily controlled by RF plasma power tuning. In order to explain the PL enhancement after the thermal treatment in UHV, we discuss the luminescence origin being closely related to the formation of nano-crystals and of optically-active defect states.