Atomic Layer Deposition of Gallium Sulfide Films Using Hexakis(dimethylamido)digallium and Hydrogen Sulfide

Abstract

Gallium sulfide (GaSx) was synthesized for the first time via atomic layer deposition (ALD), using hexakis(dimethylamido)digallium and hydrogen sulfide. The growth characteristics and surface reaction mechanism for the GaSx ALD were investigated using in situ quartz crystal microbalance, quadrupole mass spectrometry, and Fourier transform infrared spectroscopy measurements. The as-deposited films were analyzed for their surface morphology, elemental stoichiometry, chemical states and stability, and crystallinity, using a variety of characterization techniques. These measurements revealed that the GaSx growth was self-limiting in the temperature range of 125–225 °C and the growth per cycle decreased linearly with increasing temperature, from ∼1.0 Å/cycle at 125 °C to ∼0.5 Å/cycle at 225 °C. The S/Ga ratio was between 1.0 and 1.2 in the temperature range of 125–200 °C, but decreased to 0.75 at 225 °C. The GaSx films were amorphous and the refractive index increased from ∼1.8 to 2.5 with increasing temperature. Significantly, electrochemical testing showed that the ALD GaSx is a promising lithium-ion battery (LIB) anode material, exhibiting reliable cyclability and a high specific capacity of 770 mAh/g at a current density of 320 mA/g in the voltage window of 0.01–2.00 V.