The mechanism of voltage decay in corona-charged layers of silicon dioxide during UV irradiation

The charge stability in thermally grown silicon dioxide layers during irradiation with monochromatic ultraviolet light has been investigated. The samples were charged by a constant-voltage corona method. A Xenon are lamp in combination with a monochromator was used to generate mono-energetic photons. The surface potential was measured as a function of the photon energy, the irradiation intensity, the charge polarity and the substrate doping. In order to interpret the experimental results, different theoretical models were developed which consider the possibility of photo-ionization of trapped charges, multiphoton excitation in the dielectric, and injection of hot carriers from the substrate into the oxide layer. The discussion of the parameters derived from each model leads to the conclusion that electron injection from the substrate is most probably responsible for the voltage decay.