Cathodoluminescence of non-stoichiometric silica: The role of oxygen

Oxygen deficient thin silica layers SiOx with different stoichiometric degree 1 ⩽ x ⩽ 2, were prepared by thermal evaporation of silicon monoxide in vacuum and in ambient oxygen atmosphere of various pressure on crystalline silicon substrates. The chemical composition x has been determined by Fourier transform infrared spectroscopy (FTIR). Cathodoluminescence (CL) of the oxygen deficient layers shows the development of typical silica luminescence bands at the composition threshold x ⩾ 1.5 onwards to x = 2. These luminescence bands were observed at 4.3, 2.7, 2.15, and 1.9 eV. The yellow luminescence (2.15 eV) which is assigned to phase separation of SiOx into Si and SiO2 and formation of small silicon aggregates in the network is strongly increasing with the annealing temperature up to 1300 °C. On the other hand, CL spectra of oxygen ion implanted SiO2:O layers (oxygen surplus) show an intensive multimodal structure beginning in the green region at 500 nm and extending to the near IR. The energy step differences of the sublevels amount in average 120 meV and indicate vibration associated electronic states, probably correlated with O2- molecules.