Compact GaO Thin Films Deposited by Plasma Enhanced Atomic Layer Deposition at Low Temperature.

Amorphous Gallium oxide (GaO) thin films were grown by plasma-enhanced atomic layer deposition using O plasma as reactant and trimethylgallium as a gallium source. The growth rate of the GaO films was about 0.6 Å/cycle and was acquired at a temperature ranging from 80 to 250 °C. The investigation of transmittance and the adsorption edge of GaO films prepared on sapphire substrates showed that the band gap energy gradually decreases from 5.04 to 4.76 eV with the increasing temperature. X-ray photoelectron spectroscopy (XPS) analysis indicated that all the GaO thin films showed a good stoichiometric ratio, and the atomic ratio of Ga/O was close to 0.7. According to XPS analysis, the proportion of Ga and lattice oxygen increases with the increase in temperature resulting in denser films. By analyzing the film density from X-ray reflectivity and by a refractive index curve, it was found that the higher temperature, the denser the film. Atomic force microscopic analysis showed that the surface roughness values increased from 0.091 to 0.187 nm with the increasing substrate temperature. X-ray diffraction and transmission electron microscopy investigation showed that GaO films grown at temperatures from 80 to 200 °C were amorphous, and the GaO film grown at 250 °C was slightly crystalline with some nanocrystalline structures.