Photo-currents in silicon monoxide films

Measurements are reported of photo-currents in evaporated films of silicon ‘monoxide’ SiO of thickness d = 300-1400 nm, sandwiched between one thick and one semi-transparent metal electrode. One electrode was always Al, the other was Al, Cu, Mg or Ti. Dark currents I 0 as functions of voltage V show at room temperature the usual dependence log I 0 ∝ V ½/ d ½ and also show complete symmetry with respect to polarity over almost five decades of voltage quite independently of electrode materials. In the presence of illumination the photo-current δI = I─I 0 plots as straight lines log δI ∝ V ½ and shows very weak temperature dependence between 300 and 77°K. The results are interpreted on the basis of a model for Poole-Frenkel conduction involving a large density of trapping states which enable an effective carrier temperature distribution to be established in the presence of exciting radiation, independently of the lattice temperature. It is pointed out that this model may also explain certain anomalous results frequently obtained in the dark Poole-Frenkel conduction, such as low values of the β coefficient which are normally interpreted as indicating abnormally high values of dielectric constant.