High-Performance GaN-Based LEDs With AZO/ITO Thin Films as Transparent Contact Layers

The Al-doped ZnO (AZO)/indium tin oxide (ITO) bilayer films were proposed as transparent contact layers (TCLs) for the fabrication of GaN-based light-emitting diodes (LEDs). In TCLs on the p-type GaN layer, the ITO film serves as the ohmic contact layer with the thickness of only 20 nm, whereas the 300-750nm AZO films act as the current spreading layer. At an optimal AZO thickness of 500 nm, GaN-based LEDs with AZO/ITO TCLs have a forward voltage of 3.36 V, an electroluminescence emission at 526 nm with highest brightness and a large light intensity of 386 mcd at 20 mA, which are almost the same as the commercial LEDs with a 300-nm ITO TCL. The 500-nm AZO/20-nm ITO bilayer films exhibit a high transparency above 90% in the visible region, but they display a low conductivity with resistivity ~7 × 10 -3 Ω·cm. The success of GaN-based LEDs with such a relatively high-resistivity electrode strongly demonstrates that the AZO/ITO film is a very effective and practical TCL on the p-type GaN layer. The indium-saving AZO/ITO TCLs may be actually a universal approach as p-type electrodes in high-performance GaN-based LEDs for commercially mass production with low cost.