Optimization of Heteroepitaxial Gallium Oxide Thin Films on Diamond Composite Substrates using Pulsed Laser Deposition Method

Due to the large thermal and lattice mismatch between gallium oxide (Ga 2 O 3 ) and diamond, the resulting residual stress brings high defect densities and susceptibility to cracking on the Ga 2 O 3 epilayer. To balance the stress-strain behavior and eliminate the dislocation defects, this study employed diamond composite substrates which consist of a pre-grown AlN strain interlayer on the surface of the bulk diamond to heteroepitaxy Ga 2 O 3 nanomembranes via pulsed laser deposition (PLD). To achieve an optimal solution of high-quality Ga 2 O 3 thin films, several comparative investigations were proposed and gave a preliminary exploration. Subsequently, spectroscopic ellipsometry (SE), high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), were performed to characterize the physical, chemical, and optical properties. A comprehensive analysis was conducted on the quality of Ga 2 O 3 thin films dependent on the growth processes including oxygen pressure, in-situ annealing treatment, and the "two-step" growth. It demonstrated that high oxygen pressure significantly increased the growth rate of Ga 2 O 3 (∼ 2 times), slightly improved crystallinity and surface morphology (RMS decreased ∼ 2.2 nm), and reduced oxygen vacancy defects (∼ 3%). The additional in-situ annealing process and the "two-step" growth method also brought a bit of thickness increase (∼ 28 nm and ∼ 14 nm, respectively). By in-situ annealing in various stages, 2D and 3D growth modes competition caused Ga 2 O 3 thin films' continuous grain growth and fewer oxygen vacancy defects but presented different variations of surface morphology. On the whole, the "two-step" growth enhancement scheme proves the largest effect on Ga 2 O 3 's quality among the designed sets of experiments. Exploring various optimization schemes and proposing a highly reliable growth technology route is of great significance to give impetus to Ga 2 O 3 application in the electric power field. Consequently, for further insight, continuous work will be propelled in the future.