Optical properties of Ga2O3 thin films grown by atomic layer deposition using GaI3 and O3 as precursors

Abstract

Properties of Ga₂O₃ thin films grown by atomic layer deposition from GaI₃ and O₃ on Si(100) and amorphous SiO₂ substrates were investigated. The Ga₂O₃ films deposited on the bare Si and SiO₂ substrates at 450–550 °C contained the κ-Ga₂O₃ phase while it was not possible to exclude the presence of the ε-Ga₂O₃ phase in these films, either. On the substrates coated with α-Cr₂O₃, α-Ga₂O₃ was obtained at 275–550 °C. The formation of crystalline phases caused a marked increase in the density, roughness, and in the growth rate as well. The refractive indices, determined for the κ/ε-Ga₂O₃ and α-Ga₂O₃ films with thicknesses over 70 nm, were 1.96 ± 0.03 and 2.01 ± 0.02, respectively. Corresponding values of amorphous films, deposited on Si at 150–425 °C, on SiO₂ at 310 °C, and on α-Cr₂O₃/Si at 200–234 °C, were 1.86 ± 0.03 at 633 nm. The optical bandgap energies of amorphous Ga₂O₃, κ/ε-Ga₂O₃, and α-Ga₂O₃ were found to be 4.96, 5.22–5.28, and 5.28 eV in the approximation of direct optical transitions and 4.27, 4.43, and 5.09 eV, respectively, in the approximation of indirect optical transitions. The films of κ/ε-Ga₂O₃ and α-Ga₂O₃ served as effective antireflection coatings on the surface of silicon reducing the reflection down to 0.20% and 0.12%, respectively.