【Epitaxy Papers】Atomic Layer Epitaxy of (002) κ-Ga₂O₃ on c-Plane Sapphire

      Researchers from the Université Grenoble Alpes have published a dissertation titled "Atomic Layer Epitaxy of (002) κ-Ga₂O₃ on c-Plane Sapphire" in Chemistry of Materials.

Abstract

      Atomic layer epitaxy has been a powerful technique for several decades to grow epitaxial thin films of III–V and II–VI semiconducting compounds. However, the polycrystalline nature of thin films usually prevails for conducting and semiconducting binary oxides, which strongly limits their crystalline and structural quality. Here, we demonstrate the epitaxial growth of (002)-oriented κ-Ga₂O₃ thin films with a subnm surface roughness on c-plane sapphire by atomic layer deposition at 350 °C and using the relatively unexplored combination of triethylgallium and O₃ as chemical precursors. The 16 nm-thick κ-Ga₂O₃ thin films exhibit an in-plane epitaxial relationship given by (060) κ-Ga₂O₃||(300) α-Al₂O₃ and (200) κ-Ga₂O₃||(110) α-Al₂O₃. The pure epitaxial κ-Ga₂O₃ phase is further revealed using X-ray absorption near-edge structure and X-ray linear dichroism with synchrotron radiation along with transmission electron microscopy. In particular, the (004) X-ray diffraction peak for the κ-Ga₂O₃ thin film grown at 350 °C is shown to have a remarkable full-width-at-half-maximum value of 0.1° following rocking curve measurements, which is comparable to the typical lowest values reported for κ-Ga₂O₃ thick films grown by more sophisticated epitaxial chemical and physical vapor deposition techniques. The optical bandgap energy is eventually evaluated at 4.8 eV from optical transmittance spectra. These findings show the high potential of atomic layer deposition for growing epitaxial Ga₂O₃ thin films at relatively low temperatures in the framework of atomic layer epitaxy, strongly challenging the well-known epitaxial physical and chemical deposition techniques.

DOI：

https://doi.org/10.1021/acs.chemmater.5c01915