Origin of cathodoluminescence from Si nanocrystal/SiO₂ multilayers

Ion beam sputtering has been used to grow 50-period Si Ox Si O2 multilayers (MLs) and single-layer Si Ox under varying conditions of oxygen content (x). Annealing these materials at 1100 °C has led to the formation of Si nanocrystals in the Si Ox layers and some of them have been hydrogenated to passivate Si dangling bonds. The photoluminescence (PL) peak of the MLs blueshifts from 1.44 to 1.63 eV as x increases from 1.0 to 1.8. Cathodoluminescence (CL) spectra of the MLs at 77 K have two major emission bands in the near infrared (1.66 eV) and yellow (2.18 eV) 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 2.64 eV, 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 Si Ox 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.