Novel photoconductive effect in spark-processed silicon with metal contacts

Spark-processed silicon (sp-Si) has been shown to display strong photoluminescence in the UV/blue and green spectral ranges. Furthermore, ferromagnetic behavior, electroluminescence and cathodoluminescence have been reported. The present contribution reports on a novel photoconductive effect, which has been observed in a simple device made from sp-Si. A symmetric device consisting of two metal contacts on sp-Si increases its electrical conductivity dramatically when the junction of the sp-Si and the anode contact is illuminated with UV or visible light. However, its conductivity decreases when the sp-Si/cathode contact junction is illuminated. The magnitude of both effects is proportional to the intensity of the light source, and is dependent on the wavelength of the light. There is no significant change in conductivity when the bulk of the sp-Si is illuminated. This behavior is unique and strikingly different than existing devices such as p-n, p-i-n, and Schottky diodes, as well as photoconductive devices, which all show an increase in conductivity in both directions when illuminated.