【Member Papers】 First-principles study on formation and action mechanism of intrinsic Ga and O vacancy in β‑Ga₂O₃

      Researchers from Wuhan Textile University, Huazhong University of Science & Technology, and China Special Equipment Inspection & Research Institute have published a dissertation titled “First-principles study on formation and action mechanism of intrinsic Ga and O vacancy in β‑Ga₂O₃” in Computational Materials Science.

Background

      As an ultra-wide bandgap semiconductor, β‑Ga₂O₃ exhibits prominent properties including high breakdown voltage, deep-ultraviolet absorption capability and excellent Baliga figure of merit, showing great potential for next-generation high-power electronic devices, deep-ultraviolet detection and photocatalysis. However, intrinsic point defects such as gallium vacancy (V_Ga) and oxygen vacancy (V_O) can act as deep-level centers, severely compensating carriers, reducing mobility and compromising material stability, which becomes a key factor limiting device performance. Most previous studies only focused on formation energy, density of states, or two-dimensional systems, lacking systematic investigation on formation energy, thermodynamic transition levels, charge distribution, band structure, phonon spectra and binding energy of V_Ga, V_O and V_Ga‑V_O complex defects in bulk β‑Ga₂O₃. Based on first-principles calculations, the team systematically revealed the formation mechanism, charge distribution, electronic structure effects and stability of intrinsic vacancy defects, providing a quantitative theoretical foundation for understanding and regulating defect properties of β‑Ga₂O₃.

Abstract

      To gain an in-depth understanding of the formation and action mechanism of intrinsic vacancy defects in β‑Gallium Oxide (β‑Ga₂O₃), the first-principles methods are employed to systematically investigate gallium vacancy (V_Ga) and oxygen vacancy (V_O) in β‑Ga₂O₃. By comparing the formation energies of β‑Ga₂O₃ with V_Ga and V_O under different charge states and growth conditions, the most stable charge states and transition level properties of β‑Ga₂O₃ containing intrinsic vacancy defects are determined. The results reveal that V_Ga acts as deep acceptor defects and V_O functions as deep donor defects. Additionally, the calculated vacancy complexes of V_Ga‑V_O are all deep-level defects. Charge analysis further elucidates the charge redistribution during vacancy formation, showing that charge diffuses outward from the vacancy centers. Bader charge analysis indicates that Ga atoms in β‑Ga₂O₃ with intrinsic vacancy defects all lose electrons, while O atoms all gain electrons, with specific charge change values provided. Band structure calculations demonstrate that the introduction of V_Ga, V_O and V_Ga‑V_O induces the movement of the whole band towards lower energies with the emergence of impurity levels within the bandgap. Finally, stability analysis based on phonon spectra and binding energy calculations shows no dynamical stability for V_Ga, V_O and V_Ga‑V_O in β‑Ga₂O₃. This study provides a detailed quantitative description on formation and action mechanism of intrinsic vacancy defects in β‑Ga₂O₃, offering a solid foundation for understanding and regulating the defect properties of β‑Ga₂O₃.

Highlights

      Systematically reveal the formation energies and thermodynamic transition levels of V_Ga1, V_Ga2, V_O1~V_O3 and various V_Ga‑V_O complex defects in β‑Ga₂O₃

      Confirm that all intrinsic vacancies are deep-level defects, and clarify the defect properties of V_Ga as deep acceptor and V_O as deep donor

      Quantitatively clarify the charge redistribution induced by vacancy formation: Ga loses electrons, O gains electrons, and charges diffuse outward from vacancy centers

      Reveal that vacancy defects cause the overall downward shift of energy bands, appearance of impurity levels in the bandgap, and change the dispersion characteristics of CBM/VBM

      Prove for the first time that V_Ga, V_O and V_Ga‑V_O are all dynamically unstable by combining phonon spectra and binding energy, and clarify the relative stability of complex defects

Conclusion

      Based on first-principles calculations, a detailed investigation into the formation mechanism and microscopic impacts of intrinsic V_Ga, V_O and V_Ga‑V_O in β‑Ga₂O₃ is provided in this paper. Analysis of formation energies and thermodynamic transition levels reveals that all calculated configurations of V_Ga, V_O and V_Ga‑V_O act as deep-level defects in β‑Ga₂O₃. The V_Ga1 and V_Ga2 act as acceptors in n-type and O-rich environments. Similarly, the V_O1, V_O2, V_O3, V_Ga1, V_Ga2 and the V_Ga1‑V_O2 complex exhibit the donor characteristics in p-type and O-rich conditions. The charge distribution analysis indicates that charge is primarily localized around O atoms in β‑Ga₂O₃ with V_Ga, V_O, and V_Ga‑V_O. Charge density difference and bader charge analysis reveal that Ga atoms consistently lose electrons while O atoms gain electrons. The band structure analysis reveals that the introduction of vacancy defects causes the movement of the whole band towards lower energies and the emergence of impurity levels within the bandgap. Meanwhile, V_O1, V_O2 and V_O3 induce a flatting of the CBM. Notably, the V_Ga1 and V_Ga2 cause the broadening of the VBM, while the V_Ga1‑V_O3 leads to the broadening of both the VBM and the CBM. Furthermore, the phonon dispersion spectra indicates that V_Ga, V_O, and V_Ga‑V_O are unstable defects in β‑Ga₂O₃ system. Binding energy calculations further demonstrate that V_Ga1‑V_O3 is relatively stable while the V_Ga2‑V_O2 is an instable complex defect within the β‑Ga₂O₃ system.

Project Support

      This work was supported by the National Natural Science Foundation of China (NSFC) under grant number 62204178 and supported by the Open Project of Guangdong Provincial Key Laboratory of Manufacturing Equipment Digitization.