【International Papers】Intrinsic property of defective β-Ga₂O₃ to self-heal under ionizing irradiation

      Researchers from the Horia Hulubei National Institute for Physics and Nuclear Engineering have published a dissertation titled "Intrinsic property of defective β-Ga₂O₃ to self-heal under ionizing irradiation" in Scripta Materialia.

Background

      Owing to multiple disorder-induced ordering pathways (polymorphic transformations), such as β-to-γ or α-to-γ , gallium oxide (Ga₂O₃) has emerged as a promising addition to the class of polymorphic materials. Studies on the evolution and stability of irradiation-induced structures (i.e., γ-Ga₂O₃) under subsequent heavy-ion irradiation have revealed that the γ-Ga₂O₃ maintains its long-range periodicity as ion fluence increases, contrary to the behavior typically reported for other polymorphic materials. Additionally, the thermal stability of such irradiation converted γ-Ga₂O₃ structures have been verified by means of isochronal annealing experiments. These studies revealed that the crystallinity of the γ-Ga₂O₃ structure improves with increasing temperature up to 1000 K; above this temperature, the γ-Ga₂O₃ structure starts to dissolve. On the other hand, little attention, if any, has been devoted to the response of the converted γ-Ga₂O₃ polymorph structure to subsequent highly ionizing irradiation (electronic energy deposition - S_e). 

Abstract

      Damage evolution and phase stability in defective β-Ga₂O₃ and an irradiation-converted γ-Ga₂O₃ layer have been studied under ionizing irradiation at 300 K. By exploring athermal nonequilibrium processes in β-Ga₂O₃, we succeed in identifying a self-healing mechanism that enables defect recovery, characterized by a recovery cross-section of ∼0.17 nm². Remarkably, this study further demonstrates that the crystallinity of the irradiation-converted γ-Ga₂O₃ layer improves under ionizing irradiation. More importantly, X-ray diffraction analysis reveals that the highly-strained γ -phase transforms into a highly-crystalline structure without film disintegration, contrasting to that reported for isochronal annealing at 1000 K. The inelastic thermal spike calculations provide insights into the important effects of energy transfer to electrons in reordering the local atomic arrangement of both defective β-Ga₂O₃ and γ-Ga₂O₃. This behavior suggests a pathway for low-temperature crystallization, offering a promising strategy for fabricating ultrahigh-speed non-volatile memory devices.

Conclusion

      In summary, by exploring the interactions of highly ionizing irradiation with defective β-Ga₂O₃, and irradiation-induced γ-Ga₂O₃ at room-temperature, we reveal that ionization-driven athermal processes promote structural recovery in both phases. Notably, defective β-Ga₂O₃ exhibits self-healing under ionizing irradiation, with a σ_r of ∼0.17 nm². More specifically, the results show that the energy transfer of only 3.3 keV nm^-1 from ions to electrons can recover the pre-existing defects (i.e., ∼60 % of the random or amorphous structure) and remarkably restore the pristine β-Ga₂O₃ crystal structure at 300 K. Importantly, the transfer of the same low S_e value to electrons is also sufficient for converting the strained/defective γ-phase into a highly crystalline structure. The improvement of the crystallinity in this region is accompanied by a sharpening of the β/γ interface. Atomically sharp interfaces may enable the fabrication of ultrahigh-speed non-volatile memory devices. The iTS calculations provide insights into the important effects of energy transfer to electrons in the discovered self-healing mechanism. These results indicate that ionization-induced annealing can stabilize metastable polymorphic phases at low temperatures, offering new insights into the use of controlled irradiation to engineer defect states and phase stability in wide-bandgap semiconductors for advanced device applications.