EXCITONS IN CRYSTALLINE AND AMORPHOUS SIO2 - FORMATION, RELAXATION AND CONVERSION TO FRENKEL PAIRS

The consequence of creation of excitons in crystalline and amorphous SiO2, including localization of excitons by producing self-trapped excitons and formation of the E' centers in amorphous SiO2 as a result of exciton localization, is reviewed. It is emphasized that the luminescence emitted from the self-trapped excitons arises from the recombination of an electron-hole pair occupying the dangling bonds formed by the scission of an Si-O bond in the SiO2 network. A new luminescence band induced from Si-implanted SiO2 after annealing at 1100 degrees C is interpreted in terms of electron-hole recombination at the interface between Si nanocrystals and SiO2. The nature of the complementary partner of the E' center generated from an exciton is discussed. Experimental result which appear to show that the stability of the oxygen interstitials plays the major role in the annealing of the E' centers are presented. It is also suggested that the local structural change of amorphous SiO2 by ionizing radiation and amorphization under dense electronic excitation are related to the self-trapped excitons.