Charge trapping, isolated Ge defects, and photosensitivity in sputter deposited GeO₂:SiO₂ thin films

The nature of the defects in sputter-deposited GeO₂:SiO₂ thin films and their relationship to charge trapping and enhanced photosensitivity have been studied using electron paramagnetic resonance capacitance-voltage, and optical bleaching and absorption spectroscopies. We find a good qualitative agreement between the density of isolated Ge dangling bonds measured magnetically, the density of charge trapping sites measured electrically, and the density of absorbing centers measured optically. Collectively, all observations can be modeled by assuming that a change in spin state and charge state of isolated paramagnetic neutral Ge dangling bonds, to form either diamagnetic positively or negatively charged Ge sites, are largely responsible for the charge trapping and photosensitivity in these thin films.