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

Gallium sulfide (GaS x ) 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 GaS x 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 GaS x 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 GaS x films were amorphous and the refractive index increased from ∼1.8 to 2.5 with increasing temperature. Significantly, electrochemical testing showed that the ALD GaS x 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.