IWGO 2026 Session IWGO-MoA2: Defects Science II

Exploiting chemical and structural control of gallium oxide (Ga₂O₃) through doping, alloying, and epitaxy is an attractive way of further expanding the properties of this promising ultra-wide bandgap platform for next-generation power electronics. For example, Ga₂O₃ exhibits a number of (metastable) polymorphs with superior properties to the thermodynamically favored β-phase, and alloying with other elements like In and Al alloys can lead to tunability of the band gap to potentially access higher power device figures of merit, analogous to the III-nitride system but spanning a much larger rage of bandgaps exceeding 8 eV eV.[1,2] Here we survey the current understanding of dopability, common trap levels, and other types of in Ga₂O₃ and related alloys, focusing on their potential optical and electrical consequences from insights gained through first-principles-based calculations employing hybrid functionals. Specifically, we discuss what is known about the influence of crystal structure and composition on the prospects of donor doping and electrical compensation, as well the role(s) of native defects and impurities incorporated through growth and processing steps. We summarize the behaviour predicted for a number of conventional dopants and lesser-explored dopants and impurities that can impact the performance of Ga₂O₃-related materials and devices.[3-8] These results provide guidance for understanding the roles of different defect populations in the family of Ga₂O₃ polymorphs and related alloys.

This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory (LLNL) under contract DE-AC52-07NA27344.

Wafer-scale, depth-resolved inspection of threading dislocations remains a critical challenge in the development of β-Ga₂O₃ ultrawide-bandgap semiconductors. We report a laboratory-implementable, nondestructive approach for high-throughput, high-resolution, three-dimensional visualization of threading dislocations using phase-contrast microscopy (PCM). PCM can be implemented in a conventional laboratory environment under ambient conditions and achieves millisecond-scale acquisition of each field of view, providing a practical and scalable platform for rapid wafer-level inspection. The detection capability of PCM is quantitatively validated through direct comparison with synchrotron radiation X-ray topography (SR-XRT), demonstrating excellent correspondence exceeding 96% in identical regions. PCM further offers superior lateral spatial resolution, enabling the separation of closely spaced dislocations. By systematically shifting the focal plane, depth-resolved imaging of dislocation propagation through the crystal thickness is achieved, allowing three-dimensional reconstruction of dislocation networks. Projection analysis of sequential PCM images reveals dislocation trajectories and their crystallographic characteristics. These results establish PCM as an accessible and growth-relevant platform for wafer-scale, three-dimensional dislocation evaluation in β-Ga₂O₃, opening a pathway toward process feedback and reliability-oriented materials engineering.

Many Ga₂O₃ devices require the formation of heterostructures to confine charge carriers. Typically, monoclinic AlGaO alloys are used for this purpose, as the larger bandgap of Al₂O₃ results in an alloy with a conduction-band offset relative to Ga₂O₃ enabling charge carrier confinement. However, intentional n-type doping can be difficult to achieve in these alloys, with donor compensation observed in alloys with 25% Al content or higher when doped with Si. The source of this compensation cannot be ascribed to Si alone, as density functional theory (DFT) calculations predict that Si should remain shallow up to 70% Al content. This implies that another defect is acting as a compensating acceptor.

Here, we propose cation vacancies as the source of donor compensation in monoclinic AlGaO alloys. Using DFT with the HSE06 hybrid functional, we calculate the formation energies of cation vacancies in monoclinic Al₂O₃ and AlGaO₃ as compared to the Si donor. We find that the split vacancy ic configuration is also the lowest energy vacancy in Al₂O₃ and AlGaO₃. By determining the point where this vacancy becomes lower in energy than Si at the CBM as a function of alloy composition, we predict that vacancies will compensate donor doping for 16% Al content or greater under O-poor conditions and are therefore the likely source of donor compensation in monoclinic AlGaO [1].

[1] S. Seacat and H. Peelaers, https://doi.org/10.48550/arXiv.2602.02879 (2026).