Atomic Layer Deposition of Ga₂O₃ from GaI₃ and O₃: Growth of High-Density Phases

Abstract

Gallium oxide thin films, containing either α-Ga2O3 or κ-Ga2O3 crystalline phases, were grown by atomic layer deposition (ALD) by using GaI3 and O3 as precursors. The κ-Ga2O3 phase was observed in the films grown on Si(1 0 0) at substrate temperatures ≥450 °C, while α-Ga2O3 was obtained at temperatures ≥275 °C on α-Cr2O3 seed layers deposited on Si(1 0 0). The seed layers with thicknesses down to 0.7 nm appeared to be sufficient to initiate the α-Ga2O3 growth. The densities of 5.2–5.3 g/cm3 for amorphous films deposited at the substrate temperatures 150–234 °C, 5.9−6.1 g/cm3 for the films deposited on uncoated Si substrates at 450–550 °C, and 6.3−6.4 g/cm3 for the films deposited on α-Cr2O3 seed layers at 350–550 °C were determined from X-ray reflectometry measurements. The growth per cycle decreased from 0.17 to 0.05–0.09 nm with the growth temperature increase from 150 to 550 °C. Notably, the growth rates of α-Ga2O3 films on α-Cr2O3 seed layers were significantly higher at 350–450 °C than those of the films deposited on uncoated Si at the same temperatures, indicating that crystal structure influenced the growth per cycle in this ALD process. The concentration of iodine impurities did not exceed 3.2 at. % in the films deposited at 150 °C. With the growth-temperature increase to 350 °C, the concentration of impurities decreased to ≤0.04 at. % in the films grown on bare Si and ≤0.01 at. % in the films grown on α-Cr2O3 seed layers.

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

“…Consistent with the results of earlier studies, 44 the X-ray diffractograms depicted in Fig. 1 the thinner films grown at lower temperatures (Fig.…”

“…As the reflections of e-Ga 2 O 3 overlap with those of k-Ga 2 O 3 , 40,41,43,44 it is not possible to conclude on the basis of the coplanar y-2y XRD diffractograms presented in Fig. 1(a) and (c), which of these two phases was formed on bare Si and SiO 2 substrates.…”

“…40,41 Moreover, the unambiguous determination of the k-Ga 2 O 3 phase in thin films by the X-ray diffraction (XRD) method needs rather complex measurements. 43,44 This is probably one reason for the limited number of papers reporting the E g values of e-Ga 2 O 3 and k-Ga 2 O 3 . In these publications, E g values of 4.6-5 eV for e-Ga 2 O 3 45,46 and 4.9-5.14 eV for k-Ga 2 O 3 9,29,47,48 have been reported.…”

“…The self-limiting nature of atomic layer deposition (ALD) enables synthesis of thin films controlling the thickness with sub-nanometre resolution, [15][16][17][18]24,44 fabrication of conformal coatings on substrates with complex shapes, 14,15,22 and deposition of films with uniform thicknesses on large-area substrates. 18 However, the deposition of crystalline Ga 2 O 3 films on substrates that do not support epitaxial growth has been a problem for the majority of ALD processes studied so far.…”

“…However, impurities, structural defects, and surface roughness that are all related to the material synthesis method may also influence the performance of materials and thin films in various applications. Hence, proceeding from the earlier promising results, 44 the application potential of the GaI 3 -O 3 ALD process for the deposition of Ga 2 O 3 thin films for optical applications was studied in the present work. For this purpose, films containing different Ga 2 O 3 phases were deposited.…”