Low-Noise and High-Detectivity GaN-Based UV Photodiode With a Semi-Insulating Mg-Doped GaN Cap Layer

GaN-based ultraviolet photodiodes with a semi-insulating Mg-doped GaN cap layer were fabricated and characterized. Dark leakage current of the aforementioned photodiodes was much smaller than that of the conventional ones without the Mg-doped GaN cap layer due to a thicker and higher potential barrier and less amounts of interface states after inserting the Mg-doped GaN cap layer. The ultraviolet to visible rejection ratio is 3.44 x 10³ by inserting a semi-insulating Mg-doped GaN cap layer with a -IV applied bias. In this study, we also discuss the noise characteristics. It was found that minimum noise equivalent power and maximum detectivity of our photodiode were 1.2 x 10^-12 W and 9.34 x 10¹¹ cmHz^0.5 W^-1, respectively.