【International Papers】Optical Properties of Ga₂O₃ Thin Films Grown by Atomic Layer Deposition Using GaI₃ and O₃ as Precursors

      Researchers from the University of Tartu have published a dissertation titled " Optical properties of Ga₂O₃ thin films grown by atomic layer deposition using GaI₃ and O₃ as precursors " in Journal of Materials Chemistry C.

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.

Fig. 1 Coplanar θ–2θ-XRD diffractograms of (a), (b) 74–97 nm thick Ga₂O₃ films grown on (a) bare Si and (b) α-Cr₂O₃/Si substrates, and (c), (d) 185–319 nm thick Ga₂O₃ films grown on (c) SiO₂ and (d) α-Cr₂O₃/SiO₂ and α-Cr₂O₃/Si substrates. Growth temperatures and film thicknesses are shown at corresponding diffractograms. (b) The α-Cr₂O₃ seed layer thicknesses (d_SL) were 9 ± 3 nm. Miller indices of α-Ga₂O₃ (α) and κ-Ga₂O₃ (κ) are added to corresponding XRD reflections. Reflections attributable to the substrates and/or sample stage of diffractometer are marked with asterisks.

Fig. 2 Selected XRD reflections recorded in non-coplanar θ–2θ geometry at different inclination angles χ for a 210 nm thick Ga₂O₃ film grown on bare Si (solid lines) and 180 nm thick Ga₂O₃ film grown on bare SiO₂ (dotted lines). The films were grown at 450 °C.

DOI：

https://doi.org/10.1039/D4TC01846J