Evaluation of microscopic structural randomness in SiO₂ by analysis of photoluminescence decay profiles

Microscopic structural randomness in SiO₂, a typical electrical insulating material, was evaluated by observing the decay profile of the photoluminescence due to oxygen vacancies (≡Si-Si≡). As samples with different degrees of randomness, an ion-implanted thermal SiO₂ film, SiO₂ films formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane with and without doped fluorine, a buried oxide film prepared by SIMOX (separation by ion-implanted oxygen), and a bulk silica glass prepared by the soot-remelting method were tested. By analyzing the decay profile with a stretched exponential function, it was found that the deviation of the decay profile from a single exponential function is larger in the samples whose infrared absorption properties and HF etch rate suggest greater structural randomness.