Microstructure evolution and development of annealed Ni/Au contacts to GaN nanowires

Published

August 21, 2012

Author(s)

Andrew M. Herrero, Paul T. Blanchard, Aric W. Sanders, Matthew D. Brubaker, Norman A. Sanford, Alexana Roshko, Kristine A. Bertness

Abstract

The development of Ni/Au contacts to Mg-doped GaN nanowires (NWs) is examined. Current-voltage (I-V) measurements of these Mg-doped nanowire devices frequently exhibit a strong degradation after annealing in N₂/O₂. This degradation originates from the poor wetting behavior of Ni and Au on SiO₂ and the excessive void formation that occurs at the metal/NW and metal/oxide interfaces. The void formation can cause cracking and delamination of the metal film as well as reduce the contact area at the metal/NW interface, which increases the resistance. The morphology and composition of the annealed Ni/Au contacts on SiO₂ and the p-GaN films was investigated using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) measurements. Adhesion experiments were performed in order to determine the degree of adhesion of the Ni/Au films to the SiO₂ as well as observe and analyze the morphology of the film’s underside using SEM. Device degradation from annealing was prevented through the use of a specific adhesion layer of Ti/Al/Ni deposited prior to the nanowire dispersal and Ni/Au deposition. I-V of NW devices fabricated using this adhesion layer showed a decrease in resistance after annealing where all others showed an increase in resistance. Transmission electron microscopy (TEM) on a cross-section of a NW with Ni/Au contacts and a Ti/Al/Ni adhesion layer showed a lack of void formation at the contact/NW interface. Results of the XRD and TEM analysis of the NW contact structure using a Ti/Al/Ni adhesion layer suggests that Al alloying with the Ni/Au contact increases the adhesion and stability of the metal film as well as prevents excessive void formation at the contact/NW interface.

Citation

Nanotechnology

Volume

23

Issue

365203

Pub Type

Journals

Download Paper

https://doi.org/10.1088/0957-4484/23/36/365203

Local Download

Keywords

contacts, GaN, nanowire, Ni/Au

Citation

Herrero, A. , Blanchard, P. , Sanders, A. , Brubaker, M. , Sanford, N. , Roshko, A. and Bertness, K. (2012), Microstructure evolution and development of annealed Ni/Au contacts to GaN nanowires, Nanotechnology, [online], https://doi.org/10.1088/0957-4484/23/36/365203 (Accessed March 13, 2025)