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 (Ga2O3) and diamond, the resulting residual stress brings high defect densities and susceptibility to cracking on the Ga2O3 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 Ga2O3 nanomembranes via pulsed laser deposition (PLD). To achieve an optimal solution of high-quality Ga2O3 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 Ga2O3 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 Ga2O3 (∼ 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 Ga2O3 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 Ga2O3'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 Ga2O3 application in the electric power field. Consequently, for further insight, continuous work will be propelled in the future.