High brightness InGaN green LEDs with an ITO on n⁺⁺-SPS upper contact

Indium tin oxide (ITO) (260 nm) and Ni (5 nm)/Au (10 nm) films were deposited onto glass substrates, p-GaN layers, n⁺-InGaN/GaN short-period-superlattice (SPS), n⁺⁺-SPS and nitride-based green light-emitting diodes (LEDs). It was found that ITO could provide us an extremely high transparency (i.e., 95% at 520 nm). It was also found that the 1.03×10^-3 Ωcm² specific contact resistance of ITO on n⁺⁺-SPS was reasonably small. Although the forward voltage of the LED with ITO on n⁺⁺-SPS upper contacts was slightly higher than that of the LED with Ni/Au on n⁺⁺-SPS upper contacts, the 20 mA output power and external quantum efficiency of the former could reach 4.98 mW and 8.2%, respectively, which were much larger than the values observed from the latter. The reliability of ITO on n⁺⁺-SPS upper contacts was also found to be reasonably good.