Modification of electronical and optical properties in SiO₂ films by electron beam irradiation

The vibrational behaviour of amorphous SiO₂ films before and after electron irradiation with doses of 0.2 As/cm² indicates a shift of the transverse-optical oxygen bond-stretching mode at 1090 cm^-1 by about 10 cm^-1 towards lower energies and an increase of the FWHM. This softening of the infrared TO mode is compared with similar investigation of the electron dose bahaviour of cathodoluminescence (CL), secondary electron field emission (SEFE), exoelectron emission (EEE), current-voltage charge injection (I-V) as well as capacity voltage measurements (CV). E.g., in CL measurement a blue luminescence peak (460 nm resp. 2.7 eV) is created during electron beam excitation and is growing to the dominating luminescence peak in the CL spectra. The excitation-dose behaviour follows an exponential saturation and for all these methods we get a general saturation dose of (0.01-0.1) As/cm². We interpret these experimental facts as a creation of the two-fold coordinated silicon center =Si: starting from a simple oxygen vacancy as a precursor followed by subsequent structural reordering in the SiO₂ network.