Atomic scale defect formation and phase transformation in Si implanted β-Ga₂O₃

Atomic scale details of the formation of point defects and their evolution to phase transformation in silicon (Si) implanted β-Ga₂O₃ were studied using high resolution scanning transmission electron microscopy (STEM). The effect of Si implantation and the formation of defects was studied as a function of the dose of implanted atoms, and the detailed mechanism of lattice recovery was observed using both in situ and ex situ annealing of the implanted β-Ga₂O₃. The implantation created nanoscale dark spots in STEM images, which we identified as local γ-Ga₂O₃ inclusions generated by the relaxation of lattice due to ⟨010⟩ screw dislocations created by the implantation. The number and size of γ-Ga₂O₃ regions increased as the Si dose increased, and eventually the γ-Ga₂O₃ crystal phase (with stacking defects) took over the entire implanted volume when the peak Si concentration was over ∼10²⁰ cm⁻³. Annealing above 1100 °C disintegrates the local γ-Ga₂O₃ phase and returns the structure to defect-free, single crystal β phase, likely indicating that point defects (such as Si interstitials and cation vacancies) are spatially redistributed by the annealing. However, when the structure is completely transformed to γ-Ga₂O₃ by the implantation, post-annealing leaves a high concentration of dislocations within the β phase, which relates to the inhomogeneous distribution of Si atoms detected by secondary ion mass spectrometry.