Plasma-enhanced atomic layer deposition of crystalline Ga2S3 thin films

Abstract

Gallium (III) sulfide is a frontrunner for many energy storage and optoelectronic applications, which demand a deposition technique that offers a high level of control over thickness, composition, and conformality. Atomic layer deposition (ALD) is a potential technique in this regard. However, the state-of-the-art ALD processes for depositing Ga2S3 often lead to films that are amorphous and nonstoichiometric, and contain significant contaminations. Herein, we present a new plasma-enhanced atomic layer deposition (PE-ALD) process using the hexakis(dimethylamido)digallium precursor and H2S plasma coreactant to deposit high-quality Ga2S3 sulfide thin films and compare it to the thermal ALD process using the same reactants. While both cases exhibit typical ALD characteristics, substantial disparity is observed in the material properties. The PE-ALD process deposits crystalline Ga2S3 sulfide thin films at a temperature as low as 125 °C with a growth per cycle of 1.71 Å/cycle. Additionally, the PE-ALD process results in smooth and stoichiometric Ga2S3 films without any detectable carbon and oxygen contamination. Grazing incidence wide-angle x-ray scattering analysis indicates that the as-deposited Ga2S3 film crystallizes in a cubic structure with a preferred orientation along the [111] direction. The Ga2S3 film exhibits a transmittance of 70% and a bandgap of 3.2 eV with a direct transition.