Interfacial reactions of Ti/n-GaN contacts at elevated temperature

Abstract

Interfacial reactions in Ti/GaN contacts have been studied using conventional and high-resolution transmission electron microscopy (TEM), energy-filtered TEM (EFTEM), and x-ray diffraction. The thin film contacts were fabricated by evaporating Ti on n-GaN and subsequent rapid thermal annealing in argon. An x-ray result shows that the as-deposited Ti on GaN is an epitaxial hcp phase, whereas a fcc phase was identified from the as-deposited metal layer in cross-sectional TEM specimens. This phenomenon is interpreted as the transformation of hcp-Ti phase to fcc-TiHx phase by hydrogen incorporation during TEM specimen thinning. At elevated temperature, first gallium and then nitrogen diffused into the metal layer. The reaction front moved into the Ti layer, and after annealing at 700 °C many voids were formed along the Ti/GaN interface at the GaN side. A sequence of phases GaN/TiN/Ti2GaN/Ti3Ga/Ti was identified in annealed contacts, and corresponds to the expected diffusion path. The ternary phase Ti2GaN was confirmed with electron diffraction and EFTEM. A planar TiN layer, which formed in direct contact to the GaN, presumably governs the electrical properties of the alloyed contact.