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 (P(out)) via a reduction in the forward voltage (V(f)) 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 x 10 (5) whereas that of a typical Ti/Al/Ni/Au contact is 6.8 x 10(-4) cm(2), after annealing at 700 degrees 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 V(f) of the nonpolar LEDs decreases by 10% and P(out) increases by 15% when the Ni/Al/Ni/Au scheme is used instead of the typical Ti/Al/Ni/Au metal scheme. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim