Towards the Universal Transport Properties of Metal/Insulator Granular Thin Films in the Low-Field Regime with Increasing Bias Potential or Current

Abstract

Abstract-Three granular systems (Fe-Al 2 O 3 , Co-Al 2 O 3 , and Ti-SiO 2 ) had their electrical properties analyzed in the low-field regime (eV<<k B T). Even though the metals and the insulators were different, a systematic non-ohmic behavior was observed in all systems when bias or injected current were varied. The temperature dependence on the resistance was best described with the Mott variable range hopping model. It is suggested that the behavior of the electrical resistance and the electronic localization length are associated with the activation of new electronic paths between more distant grains. As these new paths configure resistances in parallel, total resistance is reduced. In the low-field regime, the resistance drop and the change in localization length seem to be universal to metal/insulator granular thin films.

Non-ohmic behavior of metal-insulator granular thin films in low-field regime (eΔV ≪ kBT)

“…The observed behavior was compatible with variable range hopping between metal grains separated by insulating barriers, as it had been observed as well with the Fe-Al 2 O 3 , Co-Al 2 O 3 , and Ti-SiO 2 granular thin films. [11][12][13][14][15] Even though it was originally developed for semiconductors, the Mott-VRH model can be applied to granular systems, because its concepts are stated in a way it is compatible with both. According to Ref.…”

“…Recently, a strong nonohmic behavior of the Fe-SiO 2 granular film was reported at room temperature. 12 We have previously reported on effects that occur in several metal-insulator granular thin films in the low-field regime, [12][13][14][15] where the non-ohmic behavior was systematically present. In our data, the thermal behavior of the resistance fitted better and over broader temperature ranges when the Mott variable range hopping (Mott-VRH) with a ¼ 1 = 4 was used, as compared to the fitting with a ¼ 1 = 2 that is used for thermally activated hopping (TAH) and Efros and Shklovskii-VRH.…”