Strain-accommodation mechanism during beta-Ga2O3 heteroepitaxy

Determine the mechanism by which strain is accommodated during the transition from an alpha-Ga2O3 wetting layer to beta-Ga2O3 islands on c-plane sapphire, particularly when beta-Ga2O3 islands coalesce into a largely relaxed film without forming misfit dislocations.

Background

The paper describes beta-Ga2O3 growth on c-plane sapphire through three-dimensional island formation, often above a thin alpha-Ga2O3 wetting layer. While the island morphology permits elastic relaxation through free surfaces, that mechanism becomes progressively ineffective as the islands coalesce into a continuous film. Experiments nevertheless observe largely relaxed beta-Ga2O3 films without misfit dislocations, creating an unresolved question about how the lattice mismatch is accommodated during growth.

The paper subsequently addresses this question using density functional theory, continuum nucleation theory, and molecular-dynamics simulations. It proposes that a localized rearrangement of gallium atoms within a single cation plane at the beta/alpha interface produces alternating alpha-like and beta-like coordination, enabling plastic relaxation while preserving the oxygen framework.

References

These observations place \ce{Ga2O3} heteroepitaxy outside the conventional framework of lattice-mismatched systems, where strain is accommodated within a single phase through well-established growth modes such as Frank-van der Merwe, Volmer-Weber, or Stranski--Krastanov. In \ce{Ga2O3}/sapphire, by contrast, the transition from $\alpha$ wetting layer to $\beta$ islands couples morphological change with polymorphic transformation, making the mechanism of strain accommodation during growth an intriguing open question.

— Plastic Relaxation without Dislocations in $β$-Ga$_2$O$_3$ Heteroepitaxy: A Structural Peculiarity of Ga$_2$O$_3$ Polymorphs  (2608.24465 - Bertoni et al., 25 Aug 2026) in Introduction, paragraph beginning “These observations place Ga2O3 heteroepitaxy outside the conventional framework”