AlGaN-based back-illuminated solar blind ultraviolet asymmetric metal-semiconductor-metal (MSM) photodetectors with high quantum efficiency have been fabricated on a sapphire substrate. To improve the performance of the Photodiodes (PDs), AlGaN absorber layer was grown on high quality AlN template on the sapphire substrate by hightemperature metal organic vapor phase epitaxy. To improve AlN template quality, high-temperature above 1300°C and low V/III ratios was applied. By inserting middle-temperature intermediate AlN layers, high-quality 2.5μm crack free 2- inch AlN template has been achieved. The XRD rocking curve full width at half maximum (FWHM) of AlN (002) is 169 arcsec, wihile the FWHM of (102) peak is 332arcsec. A 150nm AlGaN absorber layer of Al compositon 48% was further grown on the AlN template. The PL spectrum peaks at 274nm with a full width at harf maximum of 9.2nm, corresponding to the band edge emission of Al0.48Ga0.52N. The photoconductive mode was demonstrated with a Al0.48Ga0.52N PDs having different contacts. Unlike the conventional MSM photodetectors having a symmetric electrode, Ti/Al/Ni/Au and Ni/Au contact layers were deposited. The photoresponse cruve of PDs shows a sharp cut-off at 280 nm and peaks at 272nm. Owing to the high quality AlN template with the back-illuminated of the device, a solar-blind Al0.48Ga0.52N Schottky photodetectors with 28% external quantum efficiency at zero bias was achieved.
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