Characteristics of Back-illumination UV Photodetector Fabricated with AlxGa1-xN Heterostructure

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We report the growth, fabrication and characterization of an AlxGa1-xN heteroepitaxial back-illuminated UV photodetector used for flip-chip mounting. This device is grown on a one-side-polished sapphire substrate with a low-temperature AlN buffer layer by 6-pocket multi-wafer metalorganic chemical vapor deposition (MOCVD) using a vertical reactor. In order to attain the UV region, we increased the Al mole fraction in the AlxGa1-xN epilayer and acquired an AlxGa1-xN epilayer that shows a crack-free surface morphology when the Al mole fraction was 30%. This device consists of a 1.2-μm-thick Al0.3Ga0.7N "window layer", 0.16-μm-thick Al0.08Ga0.92N i-layer, 0.46-μm-thick Al0.08Ga0.92N p-layer, 0.1-μm-thick GaN p-layer and a 30-nm-thick GaN:Mg p+-contact layer. All device processes were completed by standard semiconductor processing techniques that include photolithography, metallization and etching. In this device, the zero-bias peak responsivity is measured to be about 0.1 A/W at 350 nm, which corresponds to an external quantum efficiency of 36%. The rise-and-fall time of the photoresponse is 4.1 ns. This device exhibits a low dark current density of 31.9 pA/cm2 at zero bias. Therefore, we can successfully obtain the back-illuminated UV photodetector with good responsivity, fast photoresponse time and low dark current.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2005-04-15