Metallurgical study of contacts to gallium nitride

Thermally stable contacts to GaN that also have desirable electrical characteristics are required for the further development of optoelectronic and high temperature devices based on GaN. To make improvements on existing contacts or to develop new ones, information on the metallurgy of potential contact systems is needed. In this work, the Metal-Ga-N ternary phase equilibria and the contact metallurgy are examined for Ti, Re, and Ni. Annealed contacts of these metals have been examined with x-ray diffraction and/or x-ray photoelectron spectroscopy, and the observed metallurgical reactions are discussed in light of estimated or experimentally determined Metal-Ga-N phase diagrams. Particular attention is paid to the gas phase equilibria and the role of the annealing environment on the metallurgical reactions. Finally, the consequences of this work for the design of thermally stable contacts are considered.