Characteristics of back-illuminated visible-blind UV photodetector based on AlxGa1-xN p-i-n photodiodes

In this work, we reported the growth, fabrication and characterization of an AlxGa1-xN heteroepitaxial back-illuminated visible-blind UV photodetector designed for flip-chip mounting. This device was grown on one side of a polished sapphire substrate using a low-temperature AlN buffer layer created by six-pocket multi-wafer system metalorganic chemical vapor deposition (MOCVD) with a vertical reactor. In order to obtain the wavelength of the visible-blind region, the AlxGa1-xN layer was grown under various conditions of growth time and gas flow rate, after optimizing the AlN buffer layer. This device consisted of a 1.3mum thick Al0.15Ga0.85N 'window layer', a 0.16mum thick Al0.08Ga0.92N i-layer, a 0.46mum thick Al0.08Ga0.92N p-layer, a 0.1mum thick GaN p-layer, followed by a 30nm GaN:Mg p+-contact layer. All of the device processing was completed using standard semiconductor processing techniques that included photolithography, metallization and etching. In this device, the zero-bias peak responsivity was found around 0.052A/W at 340nm, corresponding to an external quantum efficiency of 19%. The rise and fall time of the photoresponse was 20.8ns. Moreover, this device exhibits a low dark current density of 17pA/cm2 at zero-bias.