Microstructure of TiN layers used as ohmic contacts on GaN

摘要

TEM investigations have been carried out on annealed Al/Ti/GaN and directly deposited TiN films on GaN. In the Al/Ti/GaN system, the annealing step gave rise to a ～20 nm rough TiN film. The ohmic contact is made by TiN crystallites which are epitaxially related to GaN, the orientation relationship being (0001)GaN//(111)TiN. In between, amorphous patches of 1 to 2 nm extension can be found. When stoichiometric TiN was deposited directly on GaN, we obtained columnar tiN grains of 10-20 nm section, which cross the whole film thickness and are rotated mostly around the [111] axis. The epitaxial relationship is similar and no amorphous patches are observed at the interface.