The microstructure of Ti/Al and TiN ohmic contacts to gallium nitride

We carried out TEM investigations on annealed Al/Ti/GaN and directly: depos ited TiN films on GaN. In the Al/Ti/GaN system, the annealing step gave ris e to a approximate to 20 nm rough TiN film. The ohmic contact is made by Ti N crystallites which are epitaxially:related to GaN, the orientation relati onship being (0001)GaN parallel to (111)TiN. In between, amorphous patches of 1 to 2 nm extension can be found. When the stoichiometric TiN was deposi ted directly on,GaN, we: obtained columnar TiN grains of 5 to 20 nm section which cross the whole film thickness:and are rotated mostly around the [11 1] axis. The same epitaxial relationship is obtained and,;no amorphous patc hes are observed at the interface. When the GaN surface was locally termina ted by {1011} pyramidal features, the epitaxial relationship was slightly m odified; the (0001)GaN atomic planes and {111}TiN made an: angle of 5 degre es. This is found to allow the accommodation of the local misorientation of the facets and to bring about near coincidence.