AlGaN avalanche Schottky diodes with high Al-content

AlxGa1−xN-based avalanche photodiodes with a Schottky-contact grown on AlN bulk substrate with an Al-content of x = 0.68 have been examined with respect to their structural and electro-optical properties. The Schottky diodes suitable for the solar-blind ultraviolet spectral regime show avalanche gain for voltages in excess of 25 V reverse bias in linear gain mode under frontside illumination. For 60 V reverse bias, avalanche multiplication exceeding 104 was obtained. The devices were operated well below breakdown; the measured current for frontside illuminated conditions exceeds the dark-condition characteristics by more than two orders of magnitude at this voltage. The Schottky-barrier height FB and the ideality n were extracted to FB = 2.06 eV and n = 1.26 at room temperature, respectively. Temperature dependent measurements indicate a temperature insensitive dark current mechanism with an enhanced multiplication process towards lower temperatures.