Surface Polarity Dependent Photo-response of GaN MSM Ultraviolet (UV) Sensors

In this work, we fabricate and characterize ultraviolet (UV) sensors on Ga-polar and N-polar GaN structures. Heterostructure of the Ga-polar GaN structure is grown on a sapphire substrate by using metal organic chemical vapor deposition (MOCVD). Moreover, the N-polar GaN structure is prepared by using epitaxial lateral overgrowth (ELOG) and separating from the sapphire by laser lift-off (LLO). The leakage current of the Ga-polar GaN structure is six orders lower compared to that of N-polar GaN before annealing thanks to the lower dislocation density of the Ga-polar GaN structure. The UV-visible extinction ratio is almost 10² in the N-polar GaN structure, and 10⁴ in the Ga-polar GaN structure. In addition, the UV-visible extinction ratio of the Ga-polar GaN structure is greatly improved after thermal treatments at 500 ^oC and 800 ^oC. It exhibits a UV-A band-pass-like feature in the UV-visible extinction ratio of the Ga-polar GaN structure.