High performance back-illuminated MIS structure AlGaN solar-blind ultraviolet photodiodes

A back-illuminated metal–insulator–semiconductor (MIS) structure AlGaN-based solar-blind ultraviolet photodiode is demonstrated for the purpose of overcoming the technical bottleneck caused by high Al content p-AlGaN in p–i–n structure. The device presents a peak responsivity of 0.115 A/W at 270 nm, corresponding to an external quantum efficiency (EQE) of 53% and an ultraviolet/visible rejection ratio of more than three orders of magnitude under zero-bias. Moreover, a response speed around 24 µs and a peak responsivity of 0.154 A/W, corresponding to an EQE of 70.6% will be achieved at a reverse bias of 3 V. The excellent performances of the back-illuminated MIS photodetector can be attributed to the adoption of a thin n-AlGaN layer of Al content gradient which plays a role of completely relaxing the strain of light absorption layer and the introduction of a homogeneous n-AlGaN interlayer into light absorption region which redistributes its electric field in favor of the separation and transport of the photo-generated carriers.