Periodically structured amorphous silicon detectors with improved picosecond responsivity

Abstract

Enhanced optical absorption has been obtained in thin (∼30 nm) layers of hydrogenated amorphous silicon by depositing films on periodically structured substrates. At the appropriate angle of incidence, light is coupled to a surface wave in the abosrbing ‘‘artificial dielectric’’ region formed by the structured interface. This effect is used as the basis of high-speed metal a-Si:H metal detectors to overcome the conflicting requirements of high optical absorption and short transit times in thin layers. Peak response as high as 0.16 V is achieved for 50-pJ incident pulses of picosecond duration. This is comparable to that obtained with much higher mobility crystalline semi-insulators.