Epitaxial growth of atomically thin Ga2Se2 films on c-plane sapphire substrates

TL;DR

This study demonstrates the successful epitaxial growth of atomically thin Ga2Se2 films on sapphire substrates using molecular beam epitaxy, achieving high-quality surfaces and revealing growth mechanisms related to flux ratios and growth rates.

Contribution

It presents a novel method for synthesizing high-quality, atomically thin Ga2Se2 films with controlled morphology via optimized molecular beam epitaxy parameters.

Findings

Achieved Ga2Se2 films with surface roughness as low as 0.61 nm.

Demonstrated control over film thickness down to 3 tetralayers.

Identified the influence of Se:Ga flux ratio and growth rate on surface morphology.

Abstract

Broadening the variety of two-dimensional (2D) materials and improving the synthesis of ultrathin films are crucial to the development of the semiconductor industry. As a state-of-the-art 2D material, Ga2Se2 has attractive optoelectronic properties when it reaches the atomically-thin regime. However, its van der Waals epitaxial growth, especially for the atomically-thin films, has seldom been studied. In this paper, we used molecular beam epitaxy to synthesize Ga2Se2 single-crystal films with a surface roughness down to 1.82 nm on c-plane sapphire substrates by optimizing substrate temperature, Se:Ga flux ratio, and growth rate. Then we used a 3-step mode to grow Ga2Se2 films with a thickness as low as 3 tetralayers and a surface roughness as low as 0.61 nm, far exceeding the performance of direct growth. Finally, we found that the surface morphology strongly depends on the Se:Ga flux ratio, and higher growth rates widened the suitable flux ratio window for growing Ga2Se2. Overall, this work advances the understanding of the vdW epitaxy growth mechanism for post-transition metal monochalcogenides on sapphire substrates.