Solar-blind AlGaN-based p-i-n photodiodes with low dark current and high detectivity

We report solar-blind Al/sub x/Ga/sub 1-x/N-based heterojunction p-i-n photodiodes with low dark current and high detectivity. After the p+ GaN cap layer was recess etched, measured dark current was below 3 fA for reverse bias values up to 6 V. The device responsivity increased with reverse bias and reached 0.11 A/W at 261 nm under 10-V reverse bias. The detectors exhibited a cutoff around 283 nm, and a visible rejection of four orders of magnitude at zero bias. Low dark current values led to a high differential resistance of 9.52/spl times/10/sup 15/ /spl Omega/. The thermally limited detectivity of the devices was calculated as 4.9/spl times/10/sup 14/ cm/spl middot/Hz/sup 1/2/W/sup -1/.