Highly transparent ZnO spreading layer for GaN based LED

We investigated the ZnO based ohmic scheme as a transparent and low resistance contact layer on p-GaN. ZnO based contact yielded a very low specific contact resistance of 3.6 × 10–5 Ω·cm2 when annealed at 500 °C for 1 min in a nitrogen ambient, and the transparency was above 80% at wavelengths of 450 nm. In addition, we fabricated an InGaN/GaN MQW LED with a dimension of 300 × 300 µm using a transparent ZnO based ohmic contact as a current spreading layer for p-GaN in order to increase the optical output power. The GaN LED with a transparent ZnO based ohmic contact showed a decrease in the forward voltage by 0.15 V under a nominal forward current of 20 mA compared to GaN LED with Ni/Au ohmic contact. In addition, the light output power of LED with ZnO based contact was increased by 38.9% at 20 mA. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)