Photoluminescence from thermally oxidized hydrogenated amorphous silicon nanoball films fabricated by double-tubed-coaxial-line-type microwave plasma chemical vapor deposition system

Using a double-tubed-coaxial-line-type microwave plasma chemical vapor deposition (MPCVD) system, hydrogenated amorphous silicon (a-Si:H) nanoball films, which include Si nanocrystals, can be fabricated. A high deposition rate of 1600 A/s is achieved at a gas flow rate of 30 ml/min. Photoluminescence (PL) around 780 nm is observed at room temperature after the a-Si:H nanoball film is thermally oxidized in air or in pure oxygen gas. We have fabricated thermally oxidized a-Si:H nanoball films under various fabrication and oxidation conditions. As the substrate temperature during deposition becomes higher, the PL intensity decreases, and PL cannot be observed above 200°C. The PL intensity is the strongest when the substrate is set about 6 cm from the discharge tube end. As the discharge time increases, the film thickness increases and saturates, and consequently the PL intensity increases and also saturates.