ELECTRON-SPIN-RESONANCE CHARACTERIZATION OF SELF-TRAPPED HOLES IN AMORPHOUS-SILICON DIOXIDE

The electron spin resonance spectra of radiation-induced self-trapped holes (STHs) in amorphous silicon dioxide are isolated by isochronal annealing experiments and computer simulation analyses. Two distinct components, denoted STH1 and STH2 (plus a third component intermediate between the two), have been identified. The g matrices and Si-29 and O-17 hyperfine matrices of STH1 and STH2 are determined and form the bases for proposing the following models for these defects: STH1 comprises a hole trapped in the 2p orbital of a normal bridging oxygen in the glass network; it is a small polaron. STH2 probably consists of a hole rapidly tunneling between degenerate valence-band-edge states on a pair of adjacent oxygens; it is argued to be a peculiar type of Anderson localized state. Among the various radiation-induced paramagnetic centers in silica, the STHs exhibit unique isochronal anneal characteristics; these characteristics closely mimic the corresponding behavior of a component of trapped positive charge in thermally grown SiO2 films.