Re-Anodizing Technique as a Method of Investigation of Thermally Activated Defects in Anodic Alumina Films

A new approach of determination of energy of shallow thermally activated traps in the anodic alumina films is suggested. The approach consists of the heat-treatment of the anodic Al2O3|Al structure at 100-350°C (this means thermal release of electrons from the traps) and then re-anodizing of the anodic films in the barrier type electrolytes in potentiodynamic mode (refilling of electron traps during transient processes). In comparison with existing methods (thermoactivated and surface soft-X-ray absorption and photoemission spectroscopy), this method is relatively simple and can be applied to investigate electron trap levels both in semiconductor and insulator films. The algorithm of data-processing of experimental results was also proposed to obtain the parameters of thermally activated electron traps. It was applied to calculate the activation energy of electron traps that is equal to 0.147 and 0.060 eV for sulfuric and oxalic acid alumina films, respectively. The concentration of the traps was determined to be on the order of 1019 cm−3. The electron traps are believed to be due to the presence of coordinatively unsaturated aluminum ions, their presence was confirmed by FTIR spectroscopy. On the basis of data obtained a model is suggested for the transitions that take place in the barrier layer of the anodic alumina during heating and re-anodizing.