Impact of acceptor concentration on the resistivity of Ni/Au p‐contacts on semipolar (20–21) GaN:Mg

Abstract

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 NA measured by electrochemical capacitance voltage techniques. For the same Mg precursor flow and Mg/III ratio, we observe very similar acceptor densities NA of up to 1 × 1019 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 (NA > 1 × 1019 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 × 10−2. Specific contact resistivities as low as 2.4 × 10−3 Ω cm2 could be achieved. Inclusion of this p++ cap layer resulted in reduced turn on voltages in light emitting diodes with 450 nm emission wavelength.