Impact of acceptor concentration on the resistivity of Ni/Au p-contacts on semipolar (20-21) GaN:Mg
M. Rychetsky1, I.L. Koslow1,2, T. Wernicke1, J. Rass1,2, V. Hoffmann2, M. Weyers2, and M. Kneissl1,2
Published in:
phys. stat. sol. (b), vol. 253, no. 1, pp. 169-173 (2016).
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 2.4×10-3Ωcm2 could be achieved. Inclusion of this p++ cap layer resulted in reduced turn on voltages in light emitting diodes with 450 nm emission wavelength.
1 Institute of Solid State Physics, Technische Universität Berlin, Hardenbergstrasse 36 10623 Berlin, Germany
2 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
Keywords:
contacts, doping, ECV, LED, ohmic, p-GaN, semipolar.
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