Behaviour of Current in a Photographic Cell with a Semiconductor Photodetector

Abstract

The evolution of spatial periodic patterns transversal to the current flow and current-voltage characteristics of a photographic cell with semiconductor photodetector in parallel-plane geometry are studied. The photographic system with a photosensitive photodetector has been studied in a wide range of the gas pressures (21-1013 hPa), discharge gaps (10 μm-5 mm) and conductivities of the photodetector. A gallium arsenide photodetector(l0⁷-10⁸ Ω cm) has been used as the semiconducting cathode. The photodetector was irradiated on the back side with light in a particular wavelength range that was used to control the photoconductivity of the material. The photodetector was found to stabilize the discharge in the cell. The assessment of the image formation is then based on analysis of the discharge glow, visualized by a photograph taken through the SnO₂ film. When the current is increased above the stable limit, breakdown or small current and glow oscillations begin. The filamentation was primary due to the formation of a space charge of positive ions in the discharge gap which changed the discharge from the Townsend to the glow type.