Interface traps density of anodic porous alumina films of different thicknesses on Si

Impedance Spectroscopy was employed in order to investigate the electrical properties of thin porous anodic alumina films on Si, of thicknesses in the range of 50-200 nm, fabricated by anodization in sulfuric acid. C-V and G-V measurements were performed in the voltage range +5.0 V to -10.0 V and the frequency range 1 MHz to 100 Hz. The typical form of C-V and G-V curves of a metal-insulator-semiconductor (MIS) structure was obtained. The effective dielectric constant ε was calculated with a typical value of 6.5, in good agreement with previous published results. C-ω and G-ω measurements were performed as a function of the applied gate voltage in the depletion region in order to calculate the interface trap density Dit and interface trap time constant τit. Dit and τit were evaluated following the conductance method. The evaluated Dit values are of the order of 1012 eV-1 cm-2 and their observed thickness dependence is rather attributed to differences of the porous alumina/p-Si interface, introduced during the formation process, than to sample thickness