High Quantum Efficiency AlGaN/GaN Solar-Blind Photodetectors Grown by Metalorganic Chemical Vapor Deposition

We report the growth, fabrication and characterization of high-quality AlGaN/GaN solar-blind p–i–n and MSM photodetectors by low-pressure metalorganic chemical vapor deposition (MOCVD). The epitaxial layers were grown on double-polished c-plane (0001) sapphire substrates to allow for back-side illumination. The p–i–n photodiode structures typically consist of a 0.7 μm thick Al0.58Ga0.42N “window” layer, graded to a 0.2 μm thick Al0.47Ga0.53N n layer, a 0.15 μm thick Al0.39Ga0.61N i layer, a 0.2 μm thick Al0.47Ga0.53N p layer, and capped with a 25 nm GaN:Mg contact layer. At a 0 V bias, the processed p–i–n devices exhibit a solar-blind photoresponse having a maximum responsivity of 0.058 A/W at 279 nm, corresponding to an external quantum efficiency of ∼26%, uncorrected for reflections, etc. The MSM devices typically consist of an AlGaN x ∼ 0.58 window layer, and an undoped AlGaN x ∼ 0.44 absorbing layer. The MSMs exhibit an external quantum efficiency as high as ∼47% at a bias of 15 V with a peak response at 262 nm.