Charge storage and charge decay in silicon dioxide

SiO₂ layers with thicknesses between 150 nm and 2.5 μm were either thermally grown or made by chemical vapour deposition on 2-inch p-type silicon wafers. Positive or negative charging of the samples was performed by liquid-contact, corona, and electron-beam methods. The decay of the surface potential was observed isothermally at room temperature and at 350°C or by a thermally stimulated discharge (TSD) method at linearly increasing temperature. In the isothermal measurements, positively charged samples showed a somewhat faster decay than negatively charged ones. The decays can be interpreted with a simple theory based on carrier drift and compensation by conductivity. TSD peaks of negatively charged material occur at temperatures higher than those of positively charged samples. Activation energies of 1.0 and 1.4 eV for positively charged oxides and 1.9 eV for negatively charged oxides were found