Phase Transition in Cr/a-Si:H/V Thin Film Devices
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Phase Transition in Cr/a-Si:H/V Thin Film Devices J.Hu1*, A.J.Snell2, J.Hajto1, M.J.Rose3, and W.Edmiston3 1. School of Engineering, Napier University, Edinburgh EH10 5DT, Scotland, U.K. 2. Department of Electrical Engineering, University of Edinburgh, Edinburgh EH9 3JL, Scotland, U.K. 3. Department of Applied Physics and Electronics Manufacturing Engineering, University of Dundee, DD1 4HN, Scotland, U.K. * The corresponding author, whose current address is at Department of Electronics and Electrical Engineering, University of Edinburgh, Edinburgh EH9 3JL, Scotland, U.K. (Email: [email protected]) ABSTRACT Experimental results on the electronic properties of conditioned Cr/hydrogenated amorphous silicon (a-Si:H)/V thin film devices are presented. The devices under test were electro-formed, and had resistances in the range from several hundred ohms to several kiloohms. The current of conditioned devices varied non-linearly with the bias at low voltages, but exhibited `jumps' at a threshold voltage (Vth) (typically 2~3V ), leading to a resistance change of 1~3 orders of magnitude. Above Vth the current increased almost linearly with bias, and the carrier transport changed from a semiconducting behaviour into a more conducting (metallic) state. The threshold voltage Vth was found to decrease with increasing temperature and disappear at 340 ~ 350K, but recovered on reducing the temperature. The transition at Vth has been analysed in terms of electrothermal mechanism. The calculated turnover temperature is about 346K, close to that for the disappearance of Vth. We suggest that the observed transition could involve vanadium oxides such as VO2.
A12.10.1
INTRODUCTION. It has been shown by the authors that the electro-forming Cr/p+a-Si:H/V thin film structures show step-like current changes at low temperature (< 190K), as a function of increasing voltage, associated with quantised resistance [1]. After a further conditioning process, the step-like effect can be even observed at room temperature [2, 3]. Measurements on ac and dc conductivity of conditioned devices have revealed that the onset of step-like conductance is associated with the formation of an inductive component within the structure indicating a temporary formation of a metallic conduction channel under the influence of applied electric field [4]. In this paper, we report recent experimental results on the conditioned devices, measured at high temperature range of 290~360K, and therefore provide more information about the filamentary conduction process.
EXPERIMENTAL DETAILS.
The devices used for this work were Cr/a-Si:H/V sandwich structures deposited on an oxidised silicon wafer. The amorphous silicon layer, either intrinsic or doped, with a thickness of about 700~1000Å, was prepared by the RF-glow-discharge decomposition of silane (SiH4), with the contact area defined by a 10 μm diameter pore in an insulating layer. The doped a-Si:H contained 10~104ppm by volume of B2H6 . The top (V ) and bottom (Cr) metal electrodes were prepared by sputtering or vacuum evap
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