HIGH-FREQUENCY, HIGH-EFFICIENCY MSM PHOTODETECTORS

Metal-semiconductor-metal (MSM) photodiodes with submicron spaced inte rdigitated Schottky barrier fingers have been developed for applicatio ns in monolithic integrated optical receiver circuits capable of detec ting a millimeter-wave modulation signal. Each photodetector layer, is designed for optimal absorption about a narrow linewidth centered on a specific wavelength between 700 and 800 ml. The MBE grown layers con sist of: an AlxGa1-xAs cap layer, to prevent any surface recombination of carriers and to minimize top surface reflections; a thin GaAs abso rption layer (375 nm), to achieve a high-frequency response (>39 GHz) by minimizing the collection times of optically generated carriers; an d a buried Bragg reflector stack which reflects unabsorbed light back into the GaAs absorption layer. Using this layer design, we are able t o fabricate detectors that have millimeter-wave bandwidths without sac rificing quantum efficiency. The measured internal quantum efficiency of an MSM photodiode, fabricated on such a layer structure, was 82% at 5 V and close to 94% at 10 V.