【Epitaxy Papers】ALD grown (001) κ-Ga₂O₃ epitaxial thin films on c-plane sapphire: Influence of thickness and thermal annealing

      Researchers from Grenoble Alpes University‌ have published a dissertation titled " ALD grown (001) κ-Ga₂O₃ epitaxial thin films on c-plane sapphire: Influence of thickness and thermal annealing " in Journal of Materials Chemistry C.

Abstract

      Atomic layer epitaxy of high quality κ-Ga₂O₃ thin films on c-plane sapphire using atomic layer deposition (ALD) opens perspectives for optoelectronics and power electronics. However, the effects of increasing the number of cycles to thicken the κ-Ga₂O₃ film in the range of 20–100 nm are still unknown. Here, we study the ALD of epitaxial (001) κ-Ga₂O₃ thin film as a function of its thickness by varying the number of cycles from 400 to 2000. Above 20 nm, the epitaxial growth of κ-Ga₂O₃ thin films with a low surface roughness is preserved with the following relationship: (001) κ-Ga₂O₃ || α-Al₂O₃ (001), κ-Ga₂O₃ [010] || α-Al₂O₃ [10-10], and κ-Ga₂O₃ [100] || α-Al₂O₃ [11-20]. However, relaxation processes of the epitaxial strain occur, resulting in the formation of multiple rotational domains. Using thermal annealing, a full phase conversion from κ-Ga₂O₃ to β-Ga₂O₃ is shown, regardless of the thickness of the as-deposited film. The annealed Ga₂O₃ thin films grown using 400 cycles remarkably exhibit a low surface roughness along with the following epitaxial relationship: β-Ga₂O₃ (-201) || α-Al₂O₃ (001) and β-Ga₂O₃ (010) || α-Al₂O₃ (10-10). In contrast, the annealed Ga₂O₃ thin films grown using 2000 cycles have a higher structural disorder induced by the initial presence of multiple rotational domains. Furthermore, we reveal that the carbon contamination remains negligible both before and after thermal annealing. Eventually, Al/Ga inter-diffusion processes in the proximity of the interface are revealed by X-ray photoelectron spectroscopy and transmission electron microscopy after thermal annealing, resulting in the formation of an O-rich region.

DOI：

https://doi.org/10.1039/D6TC01146B