Plasma enhanced atomic layer deposition of gallium sulfide thin films

Abstract

Gallium sulfide has a great potential for optoelectronic and energy storage applications. Since most of these applications require a high control over the layer thickness or a high conformality, atomic layer deposition is a promising deposition technique. In this work, the authors present a novel plasma enhanced atomic layer deposition process for gallium sulfide based on trimethylgallium and H2S/Ar plasma. The growth was characterized using in situ spectroscopic ellipsometry. It was found that the process grew linearly at a rate of 0.65 Å/cycle and was self-limited in the temperature range from 70 to 350 °C. The process relied on a combustion reaction, which was shown by the presence of CS2 during in situ mass spectrometry measurements. Furthermore, the material properties were investigated by x-ray photoelectron spectroscopy, x-ray diffraction, and optical transmission measurements. The as-deposited films were amorphous and pinhole free. The GaSx thin films had a transmittance of >90% and a band gap of 3.1–3.3 eV.