Low temperature growth of single-phase and preferentially oriented ɛ-Ga2O3 films on sapphire substrates via atomic layer deposition

As an ultrawide-bandgap semiconductor, Ga2O3 has promising applications in electronics and optoelectronics. ɛ-Ga2O3 has attracted much attention as it performs the polarization effect, whereas single-phase and preferentially oriented ɛ-Ga2O3 films have not been prepared by the atomic layer deposition (ALD) method at low temperatures. In this paper, Ga2O3 films are prepared on sapphire substrates through the ALD method at different substrate temperatures and using different O sources. The x-ray reflectivity measured thicknesses and x-ray photoelectron spectroscopy spectra both demonstrate that the Ga source of triethylgallium cannot reacts continuously with the O source of H2O layer-by-layer. The growth rates of Ga2O3 films using O3 or PE-O2 as the O source range from 0.342 to 0.448 Å/cycle. X-ray diffraction (XRD) results indicate that the as-grown Ga2O3 films at 250 °C are amorphous, no matter using O3 or PE-O2 as the O source. They both crystallize into the single-phase and (−201) preferentially oriented β-Ga2O3 films after a high-temperature annealing of 900 °C. When the growth temperature rises to 350 °C, single-phase and (0002) preferentially oriented ɛ-Ga2O3 films occur if using PE-O2 as the O source. The full width at half maximum for the (0004) plane of ɛ-Ga2O3 from the XRD rocking curve is 0.937° while the atomic force microscopy measured surface roughness RMS is 1.24 nm. The crystal structure of the as-grown ɛ-Ga2O3 films can be maintained at an annealing temperature of 700 °C and they transform into polycrystalline β-Ga2O3 films at 900 °C. The results are beneficial for the applications of Ga2O3-based microelectronic devices.