Potential Barrier Parameters in Thin-Film Al–Al2O3-Metal Diodes

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Abstract
Internal photoelectric thresholds for collection of electrons through a thin Al2O3 layer formed by anodization in an aqueous nonsolvent electrolyte were measured as a function of photon energy, applied bias, oxide thickness, temperature, and overlayer metal. These data were analyzed in terms of photoexcitation mechanisms and optical absorption calculations to determine the potential barrier profile presented by anodized Al2O3 between metal films. The barrier profile was found to be given by the work function of the metal minus the electron affinity of the oxide, modified by the image effect for an electron between conductors and by the applied bias and the work function difference between the metals. For this agreement the electron affinity of the oxide was chosen to be approximately 2.0 eV and the high-frequency dielectric constant was used. A slight asymmetry was observed for Al–Al2O3–Al devices, possibly resulting from the metal-oxide transition regions. The potential barrier was found to increase with decreasing temperature, consistent with I-V characteristics.

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