Applications of transparent Al-doped ZnO contact on GaN-based power LED

In this study, ZnO:Al(AZO) Ni/AZO and NiO_x/AZO films were deposited on p-type GaN films followed by thermal annealing to form Ohmic contacts. After thermal annealing, the resistivities reduced from 5×10^-3 to 4.4×10^-4Ω-cm, 2.6×10^-3Ω-cm, and 1.1×10^-3Ω-cm for AZO, Ni/AZO, and NiO_x/AZO films, respectively. The Ohmic characteristic could be highly improved after inserting Ni and NiO_x between AZO and p-GaN. Both the Ni/AZO and NiO_x/AZO contacts exhibit Ohmic characteristic after annealed at 800°C in N₂ ambient. The light transmittance of Ni/AZO and NiO_x/AZO films were higher than 80% in the range of 380-700nm after the 800°C -annealing treatment. In addition, we fabricated InGaN/GaN MQW LEDs with a dimension of 1×1mm ² using the transparent Ni/AZO and NiO₂/AZO Ohmic contact as a current spreading layer for p-GaN in order to increase the light extrication efficiency. For the LED with Ni/AZO contact, the light output approach to saturation when the injection current was about 400mA. But the light output still doesn't approach to saturation when the injection current was 500mA for the LED with NiO_x/AZO contact. This may be due to that the resistivity of Ni/AZO was higher than that of NiO_x/A2O and exhibit more heavy current clouding effect. The increasing of resistivity may be due to the interdiffusion of Ni into AZO. Comparing to GaN LED with Ni/Au ohmic contact, the light output intensity of LEDs with Ni/AZO and NiO_x/AZO contacts was increased by 41% and 60% at 350mA, respectively.