Enhanced optical output power of tunnel junction GaN-based light emitting diodes with transparent conducting Al and Ga-codoped ZnO thin films

High quality Al and Ga-codoped ZnO (AGZO) thin films were successfully deposited both on sapphire substrates and GaN-based light emitting diodes (LED) with a tunnel junction (TJ) layer by using the radio frequency magnetron sputtering technique at room temperature. The AGZO thin films grown on sapphire substrate showed high transparency (96.3% at 460 nm) and low resistivity (6.8 × 10^-4Omega; cm). The AGZO thin films deposited on the GaN-based LED with a TJ layer exhibited weak ohmic behavior although it improved slightly with the annealing. The optical output power of the TJ GaN-based LED with an AGZO transparent conducting layer was about 12.6mW at 20 mA, and the external quantum efficiency was 23.0%. These values are approximately 1.7 times larger than that of the TJ GaN-based LED with a conventional Ni/Au layer.