Formation mechanism of thermally optimized Ga-doped MgZnO transparent conducting electrodes for GaN-based light-emitting diodes

We report a highly transparent conducting electrode (TCE) scheme of Mg x Zn 1-x O:Ga/Au/NiO x which was deposited on p-GaN by e-beam for GaN-based light emitting diodes (LEDs). The optical and electrical properties of the electrode were optimized by thermal annealing at 500°C for 1 minute in N 2 + O 2 (5:3) ambient. The light transmittance at the optimal condition increased up to 84–97% from the UV-A to yellow region. The specific contact resistance decreased to 4.3(±0.3) × 10 -5 Ωcm 2 . The improved properties of the electrode were attributed to the directionally elongated crystalline nanostructures formed in the Mg x Zn 1-x O:Ga layer which is compositionally uniform. Interestingly, the Au alloy nano-clusters created in the Mg x Zn 1-x O:Ga layer during annealing at 500°C may also enhance the properties of the electrode by acting as a conducting bridge and a nano-sized mirror. Based on studies of the external quantum efficiency of blue LED devices, the proposed electrode scheme combined with an optimized annealing treatment suggests a potential alternative to ITO.