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 +5.0V to -10.0V and the frequency range 1MHz to 100Hz. The typical form of C-V and G-V curves of a Metal-Insulator-Semiconductor (MIS) structure was obtained. The effective dielectric constant c was calculated with a typical value of 6.5, in good agreement with previous published results. C-omega and G-omega measurements were performed as a function of the applied gate voltage in the depletion region in order to calculate the interface trap density D-it and interface trap time constant tau(it). D-it and tau(it) were evaluated following the Conductance Method. The evaluated D-it values are of the order of 10(12) 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.