【International Papers】In situ patterned damage-free etching of three-dimensional structures in β-Ga₂O₃ using triethylgallium

      Researchers from the Arizona State University have published a dissertation titled "In situ patterned damage-free etching of three-dimensional structures in β-Ga₂O₃ using triethylgallium" in Journal of Applied Physics.

Abstract

      In this work, we report on the anisotropic etching characteristics of β-Ga₂O₃ using triethylgallium (TEGa) performed in situ within an MOCVD chamber. At sufficiently high substrate temperatures, TEGa can act as a strong etchant for β-Ga₂O₃ utilizing the suboxide reaction between Ga and Ga₂O₃ [4 Ga(s) + Ga₂O₃ (s) → 3Ga₂O (g)]. We observe that due to the monoclinic crystal structure of β-Ga₂O₃, TEGa etching on both (010) and (001) substrates is highly anisotropic in nature, in terms of both sidewall roughness and lateral etch rate. Smooth sidewalls are only obtained along crystal orientations that minimize sidewall surface energy. Utilizing this technique, we also demonstrate deep sub-micrometer fins with smooth sidewalls and high aspect ratios. Furthermore, we also demonstrate the damage-free nature of TEGa etching by fabricating Schottky diodes on the etched surface, which display no change in the net donor concentration.

Conclusion

      In conclusion, we studied the anisotropic dependence of TEGa etching on both the (001) and (010) oriented β-Ga₂O₃ substrates. We find that TEGa etching forms smooth sidewalls for features oriented along the [010] direction on (001)-β-Ga₂O₃ and along the [001] direction on (010)-β-Ga₂O₃. Smooth sidewalls are obtained due to the formation of (100) or (100) like sidewall planes with low surface energy. Furthermore, these two in-plane orientations also display the lowest lateral etch rates with a lateral to vertical etch rate ratio of ∼0.1, making them suitable for fabricating high aspect ratio 3-D structures. The damage-free nature of TEGa etching was also confirmed using electrical measurements on Ni-SBDs fabricated on the etched surface, which showed no change in the net donor concentration (N_D − N_A). This work enhances our understanding of the in situ TEGa etching and paves the way for the development of highly scaled vertical and lateral three-dimensional devices in β-Ga₂O₃.