Low resistance Ga-doped ZnO ohmic contact to p-GaN by reducing the sputtering power

Ga-doped ZnO (GZO) thin films were deposited on p-GaN as transparent conducting layers (TCLs) of GaN-based LEDs by radio-frequency (RF) magnetron sputtering. The sputtering power effects on the electrical properties of GZO contacts to p-GaN were studied. It was found that low resistance ohmic contact with a specific contact resistance of 6.0 × 10−4 Ω cm2 was achieved by reducing the sputtering power to 50 W. With increasing the sputtering power, these GZO contacts exhibited non-ohmic contact behavior. The XPS analysis indicated that the formation of gallium oxides phases at the interface and the diffusion of Zn atoms into p-GaN surface region were responsible for the degeneration of ohmic contact. In addition, due to the formation of good ohmic contact and high transmittance of GZO TCL deposited at 50 W, a low forward voltage of 3.64 V at 20 mA was realized, and the light output power was higher than that of LED with conventional ITO TCL.