LAUSR

Ti/TiN/Cu is established to be an enabling alternative to the better-known Au-based ohmic contact metals such as Ti/Al/Ni/Au. The Cu-based option delivers lower contact resistance and smoother surface morphology and is proven to be compatible with AlGaN/GaN HEMTs device processing. The TiN layer serves as an effective Cu-diffusion barrier as no detectable Cu-diffusion was observed when subjected to thermal treatment up to 600 ℃. There is a tendency of N-diffusion across the Ti/GaN interface near which N-deficiency in the GaN epitaxial layer and formation of a nano-sheath of TiN was found. This ultrathin layer of TiN works to further improve the ohmic performance of the electric contact, as reflected in lowered contact resistivity ρC. It is possible to manufacture the TiN thin films with low sheet resistance at a high deposition rate by adjusting the ratios between argon and nitrogen gas flows during sputtering deposition. Contact resistivity ρC, tested for the AlGaN/GaN HEMT devices fabricated on Si substrate according to the TLM standard were found to be as low as 3.65×10-6 Ω-cm2 (RC = 0.54 Ω-mm). The outcomes benchmark favourably against many reported metal-stacking structures for ohmic contacts. The robustness of surface morphology and interface sharpness against thermal treatments make the established ohmic stack structures suitable for scalable device fabrications.