Composition and optical properties of amorphous $a$-SiO$_x$ :H films with silicon nanoclusters

The phase composition and optical properties of hydrogenated amorphous films of silicon suboxide ($a$-SiO$_x$ :H) with silicon nanoclusters are studied. Ultrasoft X-ray emission spectroscopy show that silicon- suboxide films with various oxidation states and various amorphous silicon-cluster contents can be grown using dc discharge modulation. In films with an ncl-Si content of $\sim$50%, the optical-absorption edge is observed, whose extrapolation yields an optical band gap estimate of $\sim$3.2–3.3 eV. In the visible region, rather intense photoluminescence bands are observed, whose peak positions indicate the formation of silicon nanoclusters 2.5–4.7 nm in size in these films, depending on the film composition.