Improved aluminum-gallium-nitride (Al<sub>x</sub>Ga<sub>1-x</sub>N) p-i-n photodetectors with different active regions are reported, designed for the measurement of UV-A (315 to 380 nm), UV-B (280 to 315 nm), and UV-C (<; 280 nm) radiation. The spectral responsivity of Al<sub>x</sub>Ga<sub>1-x</sub>N photodetectors can be tailored by bandgap engineering of the Al<sub>x</sub>Ga<sub>1-x</sub>N layers and integration of filter layers. Intrinsically visible-blind p-i-n photodetectors are measured on-wafer and packaged in TO-18 headers. Photocurrent measurements in photovoltaic mode result in responsivity values of up to 0.21 A/W for UV-A (EQE = 70%), 0.14 A/W for UV-B (EQE = 56%), and 0.11 A/W for UV-C (EQE = 57%), respectively. The room temperature dark current density values as low as 30 pA/cm<sup>2</sup> at a reverse bias of -3 V yield a specific detectivity of more than 4 × 10<sup>14</sup> cm Hz<sup>0.5</sup>/W. Response time data of the p-i-n photodiodes indicate a rise time of 1.7 ns and a fall time (1/e) of 4.5 ns. Long-term stability tests over 1000 h at an irradiance of 5 W/cm<sup>2</sup> demonstrate the potential of these photodetectors for demanding applications such as the continuous monitoring of high irradiance ultraviolet light sources.
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