Abstract
In this study, β-Ga(2)O(3) thin films were epitaxially grown on Al(2)O(3)(0001) substrates via a two-step metal-organic chemical vapor deposition (MOCVD) process. The effects of growth temperatures (820 °C-920 °C) on the crystallinity, microstructure, and interfacial properties of thin films were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD θ-2θ scans confirmed that the as-grown thin films comprised a monoclinic β-phase Ga(2)O(3) layer with a pronounced out-of-plane orientation along the (-201) plane. As the growth temperature increased, the primary β-Ga(2)O(3) diffraction peaks became sharper, and the d-spacing of the (-201) plane approached that of the theoretical bulk value, indicating the progressive relaxation of tensile strain in the thin films. Rocking curves (ω scans) revealed that the full-width at half-maximum (FWHM) of the β-Ga(2)O(3)(-201) reflection narrowed from ∼2.50° (8680 arcsec) at 820 °C to ∼1.93° (6960 arcsec) at 920 °C, reflecting improved crystallinity and reduced defect density at high growth temperatures. Cross-sectional TEM revealed the epitaxial relationship of Ga(2)O(3)(-201)//Al(2)O(3)(0006) and Ga(2)O(3)[0-20]//Al(2)O(3)[-3300]. High-angle annular dark-field (HAADF) images showed an ultrathin (∼1 nm) intermediate layer with a bright contrast, which was identified as a coherently strained β-Ga(2)O(3) layer with an epitaxial orientation of β-Ga(2)O(3)(3-10)// α-Al(2)O(3)(-114). This layer served as a structural template, enabling subsequent β-phase nucleation and orientation transition along the <-201> direction. SEM results further confirmed that high growth temperatures enhanced vertical column alignment and surface smoothness. These findings highlight the critical role of interfacial phase engineering and thermal conditions in optimizing the β-Ga(2)O(3) film quality for advanced electronic and optoelectronic applications.