CONDUCTION PROCESSES AND THRESHOLD SWITCHING IN AMORPHOUS SI FILMS

Electrical conduction processes in a-Si films prepared by electron-beam evaporation in a Ti-Si-Ti sandwich structure are investigated following a switching sequence. The results show a Poole-Frenkel-type conduction above 10**4 Vcm** minus **1 but the ratio, beta //P//F/ beta //m( beta //m equals measured coefficient), varied from 0. 63 to 1. 89 within the samples investigated and temperature range. A discrete activation energy of 0. 21 eV was obtained in the region minus 75 degree C to plus 25 degree C. However, at very low temperature a T** minus **1**/**4 dependence appropriate to the hopping conductance was obtained. Further support to the above was derived from the observed power-law dependence of ac conductivity on frequency and very low activation energy. The sigma alpha omega **s graph gave a value of s equals 2. 28 which was unaffected by temperature. The higher than quadratic frequency dependence together with other few departures from theories prove that although the amorphous nature of the film is retained after ''forming'' the structure is significantly disturbed and both material and phase changes are likely. Finally, the observed opposite effects of low and high frequency on delay time is explained in terms of an electrothermal model for switching.