Improved device performance in nonpolar a -plane GaN LEDs using a Ni/Al/Ni/Au n-type ohmic contact

The authors report upon the increased light‐output power (Pout) via a reduction in the forward voltage (Vf) for nonpolar a ‐plane GaN LEDs using Ni/Al/Ni/Au n‐type ohmic contacts. The specific contact resistivity of the Ni/Al/Ni/Au contact is found to be as low as 5.6 × 10–5 whereas that of a typical Ti/Al/Ni/Au contact is 6.8 × 10–4 Ω cm2, after annealing at 700 °C. The X‐ray photoelectron spectroscopy results show that the upward surface band bending is less pronounced for the Ni/Al contact compared to the Ti/Al contact, leading to a decrease in the effective Schottky barrier height (SBH). The Vf of the nonpolar LEDs decreases by 10% and Pout increases by 15% when the Ni/Al/Ni/Au scheme is used instead of the typical Ti/Al/Ni/Au metal scheme. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) The authors report the feasibility of nonpolar a ‐plane GaN LEDs utilizing unique Ni/Al/Ni/Au n‐type ohmic contacts. The proposed LED shows a lower forward voltage and a higher output power, as compared to the reference LED using the typical Ti/Al/Ni/Au n‐type contact. These results imply that the optimization of the n‐type ohmic contact is important to improve the performance of a ‐plane GaN LEDs, due to the unique surface conditions of the a ‐plane GaN materials.