GaN/AlGaN back-illuminated multiple-quantum-well Schottky barrier ultraviolet photodetectors
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We report on characterization and operation principle of a set of GaN/AlGaN multiple-quantum-well (MQW) photovoltaic detectors. The structures were grown by molecular beam epitaxy (MBE) on c-plane sapphire substrates and fabricated in the back-illuminated vertical Schottky geometry. Introduction of MQWs into the active region of devices is expected to enhance the quantum efficiency due to the high absorption coefficient. A nearly flat spectral responsivity between 325 and 350 run with 0.054 A/W peak responsivity was achieved from the single-side polished backside (rough) illuminated GaN/AlGaN MQW devices. The cutoff wavelength of the MQW photodetector can be tuned by adjusting the well width, well composition and barrier height. A model has been developed to gain insight into the operation principles of MQWs photodiodes. The peak responsivity increased with decreasing barrier thickness due to enhanced tunneling of photogenerated carriers.