Abstract: AlxGa1-xN/GaN hetero-epitaxial front-illuminated visible-blind UV photodetectors with very high external quantum efficiency are fabricated and characterized.Light between 340～365nm can be absorbed by i-layer by penetrating the p-AlGaN layer,so the quantum efficiency can be greatly enhanced.Then the effect of the p-AlGaN thickness on the characteristics of the detector is investigated,and two devices with different p-AlGaN thicknesses (0.1μm,0.15μm) are fabricated.The measurements show that the p-AlGaN thickness can only affect the responsivity of 200～340nm light,and the quality of the i-GaN layer can greatly affect the responsivity of 340～365nm light.The device with 015μm thick p-AlGaN has much higher quantum efficiency in the 340～365nm range, and the zero-bias peak responsivity is about 0.214A/W at 365nm,corresponding to an external quantum efficiency of 856%.Moreover,this device exhibits a low dark current density of 3.16nA/cm2 at zero-bias, which indicates that the device has a very high SNR

Key words: p-i-n, AlGaN, quantum efficiency, response spectrum