Electron trapping levels in rf-sputtered Ta2O5 films

Abstract

UV-stimulated photocurrent spectroscopy and photocurrent transient methods have been used to determine the effects of deposition parameters on the electron trapping level density and its energy distribution in rf-sputtered Ta2O5 films. Results of this investigation indicate that the electron trapping level density can be greatly reduced by depositing the film at a pressure of 2×10−3 Torr with an rf-magnetron sputtering system. Experimental results also indicate the presence of the distribution for traps peaked at 2.7 eV below the conduction band in Ta2O5 films sputtered at a pressure of 2×10−3 Torr. A first-order kinetic model was used to compute trapping parameters (trap density and photoionization cross section). The results of this analysis indicate that the density of the 2.7 eV level is on the order of 4×1015 cm−3, which is three orders of magnitude lower than that for anodic Ta2O5 films, and that the photoionization cross section (at 2.7 eV) is on the order of 10−20 cm2.