Mg-annealing process for realizing ohmic contact on p-type Al0.6Ga0.4N while recovering ultraviolet light absorption

We have demonstrated a fabrication process for a ultraviolet (UV)-light-transparent ohmic contact layer on p-type Al0.6Ga0.4N, called the Mg-annealing process. By applying the Mg-annealing process on a p-GaN/p-Al0.6Ga0.4N structure, an ideal ohmic contact with a low contact resistance was preserved while the absorption of UV light with a wavelength range from 275 to 375 nm was recovered. By studying the crystallinity and surface element composition of the sample, we demonstrated that the reductions in GaN crystallinity and GaN content lead to the recovery of UV light absorption, and a UV-light-transparent MgGaN contact layer was obtained after Mg-annealing. We consider this result promising for further development of an AlGaN-based UV-LED with a high light extraction efficiency.