Formation Mechanism of Thermally Optimized Ga-Doped MgZnO Transparent Conducting Electrodes for GaN-Based Light-Emitting Diodes

Abstract

We report a highly transparent conducting electrode (TCE) scheme of MgxZn1-xO:Ga/Au/NiOx which was deposited onp-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 degrees 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) x 10(-5) Omega cm(2). The improved properties of the electrode were attributed to the directionally elongated crystalline nanostructures formed in the MgxZn1-xO:Ga layer which is compositionally uniform. Interestingly, the Au alloy nano-clusters created in the MgxZn1-xO:Ga layer during annealing at 500 degrees 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.