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 approx 20 nm rough TiN film.The ohmic contact is made by TiN crystallites which are epitaxially related to GaN,the orientation relation ship 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.