Photo-Response Switching of Flexible CdS Films Using Visible Light and Electric Field

Shielding and transmission of electro-magnetic waves (8-12 GHz) by visible light was achieved using flexible CdS films grown on a polyethersulfone polymer substrate at room temperature. The photo-resistance of the films was primarily dependent on the intensity of the visible light, and values for dark- and photo-resistance of the films at a visible light intensity of 50,000 lux were approximately 3×104 and 3×102 Ω/square, respectively. When a light-off state was followed by a light-on state, the dark resistance did not fully recover to the original resistance values. The switching characteristics of the CdS films were substantially improved by application of an electric field to the CdS films. The direct current (dc), which flows in CdS films via dc voltage, did not influence the incident electro-magnetic wave of 10 GHz to the CdS films. The dc electric field applied to the CdS films aligned the electrons and improved the collection efficiency after a light-off, resulting in complete recovery of the resistance to its original state.