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Streszczenie:
The microscopic fate of dopants introduced under nonequilibrium conditions remains largely unresolved in wide-band gap oxides. Using temperature-dependent N K-edge X-ray absorption spectroscopy, we directly resolve the local bonding configuration of implanted nitrogen in (100) β-Ga2O3. The spectra are dominated by a sharp π* resonance characteristic of N≡N bonding that systematically intensifies upon annealing, providing a direct spectroscopic fingerprint of molecular nitrogen formation. First-principles calculations and multiple-scattering simulations reproduce these spectral features and identify molecular N2 as the dominant dopant state. Rather than forming substitutional acceptors, implanted nitrogen evolves toward N2-like configurations stabilized in defect-rich environments associated with local β→γ-like structural motifs. This behavior reflects a thermally driven reconfiguration of nitrogen within the damaged layer. These results demonstrate that dopant incorporation can proceed via molecularization pathways that bypass conventional substitutional doping, providing a general mechanism for dopant deactivation under nonequilibrium incorporation conditions in oxides.

Streszczenie:
In this study, we investigate the electronic and optical properties of silicon-doped β-Ga2O3 using first-principles calculations. Four key defect configurations were analyzed: substitutional Si on a tetrahedral Ga site (SiGaI), interstitial Si (Sii9), and the interstitial Si–Ga vacancy complexes Sii9–1VGaI and Sii9–2VGaI. We confirm that the substitutional SiGaI acts as a shallow donor, raising the Fermi level into the conduction band, which is consistent with experimental data. In contrast, the interstitial Sii9 introduces a midgap level and exhibits a smaller Bader charge compared to the substitutional case, deviating from the +4-oxidation state typically observed experimentally. Crucially, complex formation with Ga vacancies stabilizes the interstitial species. The Sii9–1VGaI complex retains n-type behavior with a redshifted absorption edge. The Sii9–2VGaI complex, however, introduces deeper states and a further reduced optical absorption edge below 4 eV. The comparable Bader charge and negative formation energy of these two complexes indicate that they can coexist with substitutional donors under implantation conditions. Our results provide novel insight into the mechanism behind the experimentally observed dual nature of Si in β-Ga2O3.

Słowa kluczowe:
complex defects, density functional theory, effective band structure, Fermi energy, Ga2O3, optical absorption

Streszczenie:
Doping of β-Ga2O3 (100) with Si by ion implantation onto heated substrates is investigated. The study reveals complex ion beam-induced defect processes in β-Ga2O3, characterized by the formation of various defect types and their temperature-dependent transformation. By employing X-Ray Diffraction, Rutherford Backscattering Spectrometry, Particle-Induced X-Ray Emission, X-ray Absorption Near Edge Structure Spectroscopy, Transmission Electron Microscopy, and Density Functional Theory analyses, we examine lattice deformation, identify the local environment of dopants, assess electronic structure modifications, and verify the presence of extended defects induced by ion implantation. Our findings highlight the predominant contribution of substitutional and interstitial Si ions incorporated into complexes that act as donors manifesting n-type conductivity, while some fraction of the defects form complexes that act as traps for charge carriers. Notably, no monoclinic phase transformations were observed during implantation despite substrate temperature variations from 300 to 800 °C.

Słowa kluczowe:
β-Ga2O3, WBG, Implantation, XRD, RBS/PIXE/c, XANES, TEM, DFT, FMS

Streszczenie:
Hybrid-density-functional-theory calculations are used to evaluate the structural and electronic properties and formation energies of N-doped β-Ga2O3. Altogether, eleven interstitial (Ni) and three substitutional (NOI,II,III) impurity positions are investigated. Since direct evidence of N2 formation following the annealing of Ga2O3 and ZnO matrixes is revealed experimentally earlier, four complexes comprising two N atoms are also considered. It is determined that substitutional nitrogen defects act as deep acceptors, whereas the interstitial defects and N2-like complexes act as deep donors. Under Ga-rich growth conditions, substitutional nitrogen defects exhibit lower formation energies, with NOII defects being the most favorable. Under Ga-poor conditions, interstitial defects are more energetically desirable for a wide Fermi energy range, with Ni9 defect being the most favorable. The formation of the N2-like considered here at solely interstitial positions is energetically very expensive regardless of growth conditions. Finally, the Ni9–NOI complex is the most desirable one under Ga-rich conditions. This knowledge can serve as a basis for the development of optimal doping strategies, potentially leading to improved performance in future β-Ga2O3-based electronic devices.

Streszczenie:
In this work, hybrid density functional theory calculations are used to evaluate the structural and electronic properties and formation energies of Si-doped β-Ga2O3. Overall, eight interstitial (Sii) and two substitutional (SiGa) positions are considered. In general, our results indicate that the formation energy of such systems is significantly influenced by the charge state of the defect. It is confirmed that it is energetically more favorable for the substitution process to proceed under Ga-poor growth conditions than under Ga-rich growth conditions. Furthermore, it is confirmed that the formation of SiGaI with a tetrahedral coordination geometry is more favorable than the formation of SiGaII with an octahedral one. Out of all considered interstitial positions, due to the negative formation energy of the Si +3 charge state at i8 and i9 interstitial positions over the wide range of Fermi energy, this type of defect can be spontaneously stable. Finally, due to a local distortion caused by the presence of the interstitial atom as well as its charge state, these systems obtain a spin-polarized ground state with a noticeable magnetic moment.