【Member Papers】Xi'an University of Technology --- The impact of composite defects Vⁱₒ₍ɢₐ₎ on the electrical properties of β-Ga₂O₃/AlN heterojunctions

      Researchers from the Xi'an University of Technology have published a dissertation titled "The impact of composite defects Vⁱ_O(Ga) on the electrical properties of β-Ga₂O₃/AlN heterojunctions" in Semiconductor Science and Technology.

Acknowledgment

      This work was supported financially by the National Natural Science Foundation of China (Grant Nos. 62474139, 62104190, 61904146). This work was supported financially by Science and technology planning project of Xi’an (No. 2023JH-GXRC-0122), This work was supported financially by Natural Science Basic Research Program of Shaanxi (Program No. 2024JC-YBQN-0655). This work was supported financially by the Shaanxi Funds for Distinguished Young Scientists (2021JC-25).

Background

      Ga₂O₃ exists in five distinct polymorphs: monoclinic (β-Ga₂O₃), rhombohedral (α), defective spinel (γ), cubic (δ), and orthorhombic (ε). Among them, β-Ga₂O₃ is the most stable and has been extensively researched. β-Ga₂O₃ exhibits an exceptionally wide bandgap (∼4.8 eV) and an extremely high critical breakdown field strength (∼8 MV cm⁻¹) [1], bringing advantages such as high breakdown voltage and substantial output power. β-Ga₂O₃ exhibits a Baliga’s figure of merit 4 times higher than GaN, 10 times SiC, and 3444 times Si. This translates to lower on-resistance and reduced energy loss at the same operating voltage. Furthermore, the theoretical saturated electron velocity is approximately 2 × 10⁷ cm s⁻¹, rendering β-Ga₂O₃ highly suitable for high-frequency applications. Another major advantage of β-Ga₂O₃ is its ability to produce large-size intrinsic single-crystal substrates from the melt, and high-quality Ga₂O₃ epitaxial films of varying thicknesses can be easily grown using techniques such as metal–organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy, molecular beam epitaxy, and plasma-enhanced chemical vapor deposition. As a result, β-Ga₂O₃ has found extensive use in photodiodes, power diodes, metal-oxide-semiconductor field-effect transistors, and (Al_xGa_1-x)₂O₃/β-Ga₂O₃ MODFETs.

Conclusion

      This study employed first-principles calculations to systematically investigate the impact of composite defects (vacancy– interstitial pairs) on the electronic properties of β-Ga₂O₃/AlN heterojunction interfaces. The introduction of composite defects modifies interfacial atomic distances, with the O–N(Vⁱ_O) interface exhibiting the most significant structural changes. Composite defects possess lower formation energies compared to single defects, suggesting they are more readily formed. The O–Al interface is most susceptible to composite defect formation but exhibits poor stability, whereas the Ga–N interface forms the most stable composite defects, although their formation is the most energetically demanding. Composite defects induce partial metallicity at the O–Al and Ga–N interfaces. Defect states, primarily contributed by O and Ga atoms on the β-Ga₂O₃ side, appear within the bandgap, altering the energy positions and peak intensities of the interface states. Charge transfer from AlN to β-Ga₂O₃ is observed at all interfaces, resulting in an internal electric field pointing towards the Ga₂O₃ layer. The ideal O–N interface exhibits the strongest charge transfer, making it most conducive to forming a high-density 2DEG. While the presence of composite defects significantly reduces the magnitude of charge transfer, thereby weakening the internal electric field and diminishing the potential for high 2DEG density, the O–N(Vⁱ_O) interface maintains the highest charge transfer among the defective interfaces studied. This research provides fundamental insights into the behavior of composite defects at β-Ga₂O₃/AlN heterojunction interfaces and their influence on electronic properties, offering valuable theoretical guidance for the design and optimization of high-performance electronic devices based on this heterostructure.