Origin of cathodoluminescence from Si nanocrystal/SiO2 multilayers

Ion beam sputtering has been used to grow 50-period SiOx∕SiO2 multilayers (MLs) and single-layer SiOx under varying conditions of oxygen content (x). Annealing these materials at 1100°C has led to the formation of Si nanocrystals in the SiOx layers and some of them have been hydrogenated to passivate Si dangling bonds. The photoluminescence (PL) peak of the MLs blueshifts from 1.44to1.63eV as x increases from 1.0 to 1.8. Cathodoluminescence (CL) spectra of the MLs at 77K have two major emission bands in the near infrared (1.66eV) and yellow (2.18eV) spectral ranges at x=1.0, which are referred to as low-energy (LE) and high-energy (HE) bands, respectively. As x increases up to 1.8, the LE and HE CL bands show blueshifts to 2.16 and 2.64eV, respectively, which are more than two times stronger than the PL. After hydrogenation, the CL intensities are enhanced more greatly at larger x. Through these and other experimental data including CL spectra of the single-layer SiOx and the effect of temperature on the CL of the MLs, the HE and LE bands are shown to be nanocrystal related and others defect related.