Improvement in performance of GaN-based light-emitting diodes with indium tin oxide based transparent ohmic contacts

Abstract

InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with indium tin oxide (ITO) and Ni/Au p-contacts were fabricated. ITO (500 nm) and Ni/Au (2 nm/9 nm) films were deposited onto p-GaN epitaxial layers by an e-beam evaporation system. For the LEDs using in situ annealed ITO and Ni/Au films as p-contacts, the forward voltage at 20 mA was 3.5 and 3.2 V, respectively. Under the same amount of injection current, the LED with in situ annealed ITO p-contact had higher output electroluminescence (EL) intensity and larger light output power. The EL intensities and the light output power of ITO LEDs were enhanced by 85% and 60%, respectively, at 20 mA. As a result, the light output and power conversion efficiency of ITO LEDs on GaN were greatly improved at high injection currents. The fabricated LEDs were subjected to a stress test at 30 mA and 55 °C and showed a very small degradation of optical power (<1% decrease) for 24 h. The light output of MQW LEDs keeps 80% of the original value after 1000 h stressing. Therefore, the fabricated LED devices have demonstrated a good reliability.