Effect of post-metallization anneal on (100) Ga2O3/Ti-Au ohmic contact performance and interfacial degradation

Here, we investigate the effect of post-metallization anneal temperature on Ti/Au ohmic contact performance for (100)-oriented Ga2O3. A low contact resistance of similar to 2.49 x 10(-5) Omega.cm(2) is achieved at an optimal anneal temperature of similar to 420 degrees C for (100) Ga2O3. This is lower than the widely-used temperature of 470 degrees C for (010)-oriented Ga2O3. However, drastic degradation of the (100)-oriented contact resistance to similar to 1.36 x 10(-3) Omega.cm(2) is observed when the anneal temperature was increased to 520 degrees C. Microscopy at the degraded ohmic contact revealed that the reacted Ti-TiOx interfacial layer has greatly expanded to 25-30 nm thickness and GaAu2 inclusions have formed between (310)-Ga2O3 planes and the Ti-TiOx layer. This degraded interface, which corresponds to the deterioration of ohmic contact properties, likely results from excess in-diffusion of Au and out-diffusion of Ga, concurrent with the expansion of the Ti-TiOx layer. These results demonstrate the critical influence of Ga2O3 anisotropy on the optimal post-metallization anneal temperature. Moreover, the observed Ti/Au contact degradation occurs for relatively moderate anneal conditions (520 degrees C for 1 min in N-2), pointing to the urgent necessity of developing alternative metallization schemes for gallium oxide, including the use of Au-free electrodes. (C) 2022 Author(s).

Automated summary

The effect of post-metallization anneal temperature on Ti/Au ohmic contact performance for (100)-oriented Ga2O3 was investigated. An optimal anneal temperature of around 420°C resulted in low contact resistance, but a drastic degradation occurred at 520°C with the formation of GaAu2 inclusions and an expanded Ti-TiOx interfacial layer at the degraded ohmic contact site. The findings emphasize the critical influence of Ga2O3 anisotropy on the optimal post-metallization anneal temperature and suggest the need for alternative metallization schemes for gallium oxide.