Temperature and field effects on the conduction mechanisms in semi - insulating polycrystalline silicon

We have studied the temperature dependence of electrical conductivity in semi-insulating polycrystalline silicon (SIPOS) layers deposited on SiO2 with and without transverse electric fields for oxygen concentrations ranging from 2 to 30 at. % o. At 30 at. % O, for transverse fields of the order of 10⁶ V/cm, the room temperature conductance increases by a factor ¿300 with respect to weak transverse field conditions. The results are interpreted by assuming that carrier transport is controlled by thermoionic field emission and by Frenkel generation of carriers at the grain boundaries. The comparison of the carrier transport fitting parameters with the transmission electron microscopy data on grain size supports a model of SIPOS structure in which each silicon grain is surrounded by a SiO2 shell which becomes continuous at large oxygen contents.