Transmission electron microscopy was utilized to elucidate the post-annealing interfacial microstructure of Ti/Al/Mo/Au metallization with AlGaN/GaN heterostructures to gain insight into the formation mechanism of low-resistance ohmic contacts. The reaction between the metal and the AlGaN layer did not proceed uniformly. Localized penetration through the AlGaN layer beyond the two-dimensional electron gas (2DEG) was observed while partial consumption of the AlGaN layer was noted in other areas. Analytical transmission electron microscopy analyses confirmed that the main reaction product was TiN. A correlation between the appearance of TiN islands and threading dislocations was observed. Threading dislocations serve as short-circuit diffusion channels, and were responsible for the non-uniform reaction. TiN islands had a large total area of intimate contact with the 2DEG, and since no tunnelling of electron through the AlGaN was required, a low-resistance ohmic contact was obtained.

Dislocation-Induced Non-Uniform Interfacial Reactions of Ti/Al/Mo/Au Ohmic Contacts on AlGaN/GaN Heterostructure. L.Wang, F.M.Mohammed, I.Adesida: Applied Physics Letters, 2005, 87[14], 141915 (3pp)