Impact Of Acceptor Concentration On The Resistivity Of Ni/Au P-Contacts On Semipolar (20-21) Gan:Mg

The p-type doping of GaN with Mg, in particular doping of p(++) cap layers and its influence on the resistivity of Ni/Au contacts on semipolar (20-21) GaN, has been investigated. For this purpose, we have compared GaN: Mg grown on several semipolar and polar orientations with respect to the acceptor concentration N-A measured by electrochemical capacitance voltage techniques. For the same Mg precursor flow and Mg/III ratio, we observe very similar acceptor densities N-A of up to 1 x 10(19) cm(-3) for (0001), (20-21), (20-2-1), and (11-22) GaN:Mg. Furthermore, the impact of the II/III ratio for the p(++) cap layer (N-A > 1 x 10(19) cm(-3)) on I-V characteristics of Ni/Au (20 nm/30 nm) contacts on (20-21) oriented GaN: Mg has been investigated. Ohmic I-V characteristics were observed for Mg/III ratios >1 x 10(-2). Specific contact resistivities as low as 2.4 x 10(-3) Omega cm(2) could be achieved. Inclusion of this p(++) cap layer resulted in reduced turn on voltages in light emitting diodes with 450 nm emission wavelength. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim