A Schottky-Type Metal-Semiconductor-Metal Al_0.24Ga_0.76N UV Sensor Prepared by Using Selective Annealing

Asymmetric metal-semiconductor-metal (MSM) aluminum gallium nitride (AlGaN) UV sensors with 24% Al were fabricated using a selective annealing technique that dramatically reduced the dark current density and improved the ohmic behavior and performance compared to a non-annealed sensor. Its dark current density at a bias of -2.0 V and UV-to-visible rejection ratio (UVRR) at a bias of -7.0 V were 8.5 × 10^-10 A/cm² and 672, respectively, which are significant improvements over a non-annealed sensor with a dark current density of 1.3 × 10^-7 A/cm² and UVRR of 84, respectively. The results of a transmission electron microscopy analysis demonstrate that the annealing process caused interdiffusion between the metal layers; the contact behavior between Ti/Al/Ni/Au and AlGaN changed from rectifying to ohmic behavior. The findings from an X-ray photoelectron spectroscopy analysis revealed that the O 1s binding energy peak intensity associated with Ga oxide, which causes current leakage from the AlGaN surface, decreased from around 846 to 598 counts/s after selective annealing.