Low-noise back-illuminated AlxGa1-xN-Based p-i-n solar-blind ultraviolet photodetectors

We report the growth, fabrication and characterization of Al0.4Ga0.6N-Al0.6 Ga0.6N back-illuminated, solar-blind p-i-n photodiodes. The peak responsivi ty of the photodiodes is 27 and 79 mA/W at lambda approximate to 280 mn for bias voltages of 0 V and -60 V, respectively, with a UV-to-visible rejecti on ratio of more than three decades (at 400 nm), These devices exhibit very low dark current densities (similar to5 nA/cm(2) at -10 V), At low frequen cies, the noise exhibits a 1/f-type behavior. The noise power density is S- 0 approximate to 5 x 10(-25) A(2)/Hz at -12.7 V and the detectivity (D*) at 0 V is estimated to be in the range of 4 x 10(11)-5 x 10(13) cm.Hz(1/2)/W. Time-domain pulse response measurements in a front-illumination configurat ion 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 Al0.4Ga0.6 N layer.