Low-noise and high-detectivity GaN-B ased 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 ×10³ by inserting a semi-insulating Mg-doped GaN cap layer with a -1 V 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 × 10^-12 W and 9.34 × 10¹¹ CmHz ^0.5W^-1, respectively.