Effect of gamma ray irradiation on the conduction mechanisms of radio-frequency-sputtered Ta2O5 films

The microstructural and electrical conduction properties of sputtered Ta2O5 films pre-irradiated and gamma-ray-irradiated were systematically investigated. Analytical results revealed that the crystallinity and the leakage current of the pre-irradiated sample were effectively improved by raising the irradiation dose at low doses of irradiation [1 M similar to 4M rad(Ta2O5)]; however, higher doses of gamma-ray irradiation [>4 M rad(Ta2O5)] undesirably deteriorated the film crystallinity, yielding a larger leakage current. Such a result leads the Frenkel-Poole conduction (pre-irradiated sample) transformed to Schottky emission conduction process [low doses (1 M similar to 4 M rad(Ta2O5)) of gamma-ray-irradiated samples] and then gradually to the Frenkel-Poole conduction [high doses (>4 M rad(Ta2O5)) of gamma-ray-irradiated samples] again. The electrode-limited Schottky emission conduction effect dominantly occurring in the 1 M and 4 M rad(Ta2O5)-irradiated samples was deduced to be due to the repair of oxygen deficiency and the superior crystallinity of the Ta2O5 films caused by the low doses of gamma-ray irradiation. Contrarily, the major mechanism of bulk-limited Frenkel-Poole conduction happened in the pre-irradiated and 12 M rad(Ta2O5)-irradiated samples was suggested to be due to the deteriorated crystallinity and considerable oxygen vacancy in the Ta2O5 films.