Performance comparison of front- and back-illuminated AlGaN-based metal–semiconductor–metal solar-blind ultraviolet photodetectors

In this work, AlGaN-based metal–semiconductor–metal solar-blind ultraviolet photodetectors (PDs) with low dark current were fabricated on sapphire substrates. In both front- and back-illumination operation modes, the PDs exhibited sharp photoresponse cutoffs at ∼280 nm with solar-blind/ultraviolet rejection ratios of more than 103. The quantum efficiency of the back-illuminated PD was observed to generally be higher than that of the front-illuminated PD. Nevertheless, at very low bias range, the front-illuminated PD exhibited greater photoresponsivity. The observed performance differences of the PDs in the different illumination modes are discussed in terms of surface reflectivity and photocarrier collection efficiency.