CATHODOLUMINESCENCE AND CATHODOELECTROLUMINESCENCE OF AMORPHOUS SIO2-FILMS

Cathodoluminescence of amorphous SiO2 films thermally grown on a Silic on substrate has been observed in a scanning electron microscope using wavelength dispersed registration by a charge coupled device (CCD) ca mera. Spectra have three bands: at 650 nm (red), 460 nm (blue), and 28 5 nm (UV) whose intensities change during the initial period of electr on beam excitation. Luminescence peak dose dependence has been investi gated in a wide range of current density (10(-5) to 10(-3) A cm(-2)) a nd temperature (90 to 500 K). An interpretation of the dose-temperatur e dependence is made by a model of precursor transformation via a meta stable interlevel. Application of an electric field during continuous electron excitation (cathodoelectroluminescence) causes an enhancement up to five times of the blue band intensity. On the other hand, the r ed band decreases in I-he electric field. Based on these phenomena, th e UV and the blue luminescence band are attributed to an internal elec tron impact excitation within a localized center, probably twofold-coo rdinated silicon in the SiO2 network, whereas the red band is ascribed to band-to-band-recombination via localized levels attributed to non- bridging oxygen. (C) 1997 Elsevier Science B.V.