Transmission electron microscopy analysis of interfacial layers in Ti/Ta/Al ohmic contacts to n-AlGaN

Structure of the interfacial layers of Ti/Ta/Al ohmic contacts to AlGaN/GaN/sapphire has been investigated by high-resolution electron microscopy (HREM). HREM, optical diffractograms, and image simulations showed that TiN (∼10.0 nm) and Ti3AlN (∼1.4 nm) interfacial layers form at the interface between the Ti layer and the AlGaN during the annealing. The cubic Ti3AlN layer has a lattice parameter of 0.411±0.003 nm with the space group Pm3m matching that of AlGaN. A model of the atomic arrangements of the Ti3AlN/Al0.35Ga0.65N interface is proposed. This model is supported by a good match between the simulated and the experimental image.