Investigation of indium–tin-oxide ohmic contact to p-GaN and its application to high-brightness GaN-based light-emitting diodes

Abstract

Indium–tin-oxide (ITO) contacts to p-GaN exhibit ohmic characteristics by inserting a 10-nm-thick p-In 0.1Ga 0.9N layer as an intermediate. The specific contact resistivity of 4.5 × 10 −2 Ω cm 2 was obtained while annealing ITO/p-GaN contacts at 500 °C. Based on the variation of contact resistivity with respect to temperature, the dominant transport mechanism of ITO/p-GaN structure tended from thermionic field emission to thermionic emission when the post-annealing temperature was raised from 400 °C to 600 °C. From the XPS, XRD and SIMS results, the outdiffusion of gallium atoms and the formation of Ga–O bonds could introduce the gallium vacancies and increase the net concentration of holes, which would benefit the carrier tunneling through the interface. The GaN-based light-emitting diodes (LEDs) with 500 °C-annealed ITO contacts exhibited the forward voltage of 3.43 V and output power of 4.30 mW at a 20-mA-current injection. Although the forward voltage showed a little higher than the conventional LEDs by 0.2 V, the external quantum efficiency and power efficiency were enhanced by about 46% and 36%, respectively. As for the life test, LEDs with 500 °C-annealed ITO contacts presented a similar reliability as the conventional LEDs. Therefore, ITO contacts can make GaN-based LEDs highly bright and reliable in practice.