Atomic Scale Investigation of Point and Extended Defects in Ion Implanted β-Ga₂O₃

Atomic scale scanning transmission electron microscopy (STEM) was used to study the formation of point and extended defects, as well as phase transformations in Si-implanted <i>β</i>-Ga₂O₃. Quantitative analysis of the atomic column intensities in STEM images acquired with an absolute scale, when combined with precise electron scattering simulations, can directly visualize the detailed structure of atomic and nanoscale defects in materials. For example, our previous studies have revealed the formation of different types of point and extended defects, including the interstitial-divacancy complexes in <i>β</i>-Ga₂O₃ and planar defects and phase transition in (Al_xGa_1−x)₂O₃ that directly correlate with Al incorporation into the lattice. In the present study, we performed a correlative study on the structural change and defect formation in Si implanted <i>β</i>-Ga₂O₃ (edge-defined, film-fed (EFG)-grown (001) <i>β</i>-Ga₂O₃ substrate) as a function of Si dose, using a combination of STEM and secondary ion mass spectrometry (SIMS). Peak Si concentrations of 10¹⁸-10²¹ cm^-3 were investigated. Different types of point defects and their complexes were observed in lower Si concentrations (&lt; ~ 10¹⁹ cm^-3), which include cation interstitials and substitutional atoms into the oxygen positions. The types and concentrations of those defects change as a function of the depth of the implantation. The implication of the observed defects to electronic properties will be discussed. High concentration of point defects at a local region also led to the formation of a unique type of extended defect, which apparently involves a large strain field that extends up to a few tens of nanometers. At higher Si concentrations (&gt; 10²⁰ cm^-3), the structure tends to transform into different Ga₂O₃ phases, including γ-Ga₂O₃ which, according to our previous investigation, has a close relationship to the extended defects in <i>β</i>-Ga₂O₃. In situ annealing of the samples was performed to understand the structural evolution and diffusion dynamics of the implanted materials. The precise atomic scale information on defect formation and their evolution provides an important guidance to understand and control the ion implantation of Ga₂O₃ materials and devices which is crucial to advance them to next generation ultrawide-bandgap applications.