Photodetectors or photosensors have played a crucial role in military science and technology (particularly infrared detectors) for several decades. Their applications are also evident in diverse industries where switching with light intensity is employed. The principle of photoconductivity is used in various devices such as smoke detectors, solar energy cells, sensors, radiation, and electromechanical choppers. There is no limit to the practical applications, and now the importance of photodetectors is increasing because of the proliferation of optical communications. Because of recent technological developments, monolithic integration of ultrahigh-speed photonic devices has become a reality and the design of optical computers is the next logical step.