Study of Ti contacts to corundum α-Ga₂O₃

We present a study of the electrical, structural and chemical properties of Ti contacts on atomic layer deposited α-Ga₂O₃ film. Ti forms an ohmic contact with α-Ga₂O₃. The contact performance is highly dependent on the post-evaporation annealing temperature, where an improved conductivity is obtained when annealing at 450 °C, and a strong degradation when annealing at higher temperatures. Structural and chemical characterisation by transmission electron microscopy techniques reveal that the electrical improvement or degradation of the contact upon annealing can be attributed to oxidation of the Ti metallic layer by the Ga₂O₃ film in combination with the possibility for Ti diffusion into the Au layer. The results highlight that the grain boundaries and inclusions in the Ga₂O₃ film provide fast diffusion pathways for this reaction, leaving the α-Ga₂O₃ crystallites relatively unaffected—this result differs from previous reports conducted on β-Ga₂O₃. This study underlines the necessity for a phase-specific and growth method-specific study of contacts on Ga₂O₃ devices. (paper)