Low-noise back-illuminated Al/sub x/Ga/sub 1-x/N-based p-i-n solar-blind ultraviolet photodetectors

We report the growth, fabrication and characterization of Al/sub 0.4/Ga/sub 0.6/N-Al/sub 0.6/Ga/sub 0.4/N back-illuminated, solar-blind p-i-n photodiodes. The peak responsivity of the photodiodes is 27 and 79 mA/W at /spl lambda//spl ap/280 nm for bias voltages of 0 V and -60 V, respectively, with a UV-to-visible rejection ratio of more than three decades (at 400 nm). These devices exhibit very low dark current densities (/spl sim/5 nA/cm/sup 2/ at -10 V). At low frequencies, the noise exhibits a 1/f-type behavior. The noise power density is S/sub 0//spl ap/5/spl times/10/sup -25/ A/sup 2//Hz at -12.7 V and the detectivity (D*) at 0 V is estimated to be in the range of 4/spl times/10/sup 11/-5/spl times/10/sup 13/ cm/spl middot/Hz/sup 1/2//W. Time-domain pulse response measurements in a front-illumination configuration indicate that the devices are RC-time limited and show a strong spatial dependence with respect to the position of the incident excitation, which is mainly due to the high resistivity of the p-type Al/sub 0.4/Ga/sub 0.6/ N layer.