High gain, large area, and solar blind avalanche photodiodes based on Al-rich AlGaN grown on AlN substrates

We demonstrate large area (25000 mu m(2)) Al-rich AlGaN-based avalanche photodiodes (APDs) grown on single crystal AlN substrates operating with differential (the difference in photocurrent and dark current) signal gain of 100000 at 90 pW (<1 mu W cm(-2)) illumination with very low dark currents <0.1pA at room temperature under ambient light. The high gain in large area AlGaN APDs is attributed to a high breakdown voltage at 340V, corresponding to very high breakdown fields similar to 9 MV cm(-1) as a consequence of low threading and screw dislocation densities < 10(3)cm(-2). The maximum charge collection efficiency of 30% was determined at 255nm, corresponding to the bandgap of Al0.65Ga0.35N, with a response of 0.06A/W. No response was detected for lambda > 280nm, establishing solar blindness of the device.