Thermally stimulated ionic conductivity of sodium in thermal SiO2

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Abstract
The effect of Na+ concentration, oxide thickness, applied field, and metal electrode on thermally stimulated ionic conductivity (TSIC) measurements of positive‐ion motion in SiO2 grown on single‐crystal silicon has been studied. A surface trapping model, assuming blocking electrodes, has been used to analyze TSIC curves. Using a hyperbolic hearing rate (1/T ∝ time), for which analytic expressions for normalized first‐order TSIC curves are obtained, both energies E and preexponential factors s appropriate to the detrapping processes are obtained. Two distinct positive‐charge peaks are observed in TSIC curves. The magnitude of the low‐temperature peak, the α peak, is proportional to the amount of Na+ introduced into the sample. At high fields, the magnitude of the high‐temperature peak, the β peak, is independent of the evaporated Na+ concentration; its origin is uncertain but it may be due to mobile hydrogen. The temperature for the maxima in the TSIC curves, Tm, decreases with field for both the α and β peaks. At Na+ concentrations below 2×1012 Na+/cm2, the β peak is dominant in TSIC curves. Na+ motion from the Au‐SiO2 interface during the first heating of Au‐SiO2‐Si samples follows the simple model for release of Na+ from interface traps. On the other hand, Na+ motion from the Al‐SiO2 interface on the first heating of Al‐SiO2‐Si samples occurs at lower temperatures than for Au‐SiO2‐Si samples and appears to depend on reaction between Al and SiO2 rather than on a simple trap‐release process. Na+ release from traps at the Si‐SiO2 interface is similar with both Al and Au electrodes, and occurs at lower temperatures than for Na+ release from the metal‐SiO2 interface.