Impedance study of aging porous silicon films

Abstract

The electrical properties of luminescent porous silicon layers (PS) were studied using a method of ac impedance spectroscopy in a range of electric field frequencies 0.175–10 5Hz (amplitude 1 V) and temperatures 20–150 °C. It was found that two processes are responsible for the impedance properties of PS: the relaxation process with characteristic time of about 3 × 10 −4s and a low-frequency conductivity of Warburg type. An electric equivalent circuit was designed ensuring good fit of the experimental data acquired at differently treated PS samples. The components of the equivalent circuit were assigned to physical elements of PS (an amorphous phase at the top of PS and a layer of underlying bulk PS material). Different post-growth treatments (training by ac electric field and increasing temperature, pore filling by inert electrolyte, evacuation at increased temperatures) result in changing the properties of the PS samples. This is interpreted in terms of an existence of residuals of the electrolyte inside the pores and their influence onto the aging stability of PS.