Low-Temperature Photocurrent Spectroscopy on Localized States in SiO2Films

Photoionization of an electron trap in vitreous Si${\mathrm{O}}_2$ films was measured between 6 and 300 K. The photoionization threshold decreased monotonically with increasing temperature and film thickness. A thermal broadening of the ionizing transition was proportional to ${coth}^{\frac{1}{2}}\left(\frac{\tau }{2T}\right)$ where $\tau =129\mathrm{}$ K and $T$ is temperature in kelvins. These characteristics of the photoionization response were similar to those reported for color-center optical absorptions in single crystals, and were related to static and dynamical strains in the oxide film.