Spatially Resolved Phase Transition and Modifications in Gallium Oxide

Gallium Oxide (Ga₂O₃) is a promising ultra-wide bandgap semiconductor material that has garnered significant attention due to its ease of large-scale production through melt growth and its high break-down voltage. Beta (β)-Ga₂O₃ is the most thermally and chemically stable polymorph among the various forms of Ga₂O₃. Unfortunately, the control and manufacturing of other phases on the nanoscale remain immature due to the metastable nature of those phases.

Azarov et al. demonstrated that β to gamma (γ)-Ga₂O₃ phase transition is possible after reaching a certain critical damage level (dpa) induced by ion irradiation. Various ion implantation experiments have shown that the phase transition is independent of the chemical nature of the implanted ion. Interestingly, the structure retains its crystal order up to 260 dpa before amorphization, which is quite higher than most radiation-tolerant materials (AlN, SiC). The stability of the oxygen lattice against ion irradiation is the main reason for the high radiation tolerance of Ga₂O₃.

Here, helium ion microscopy (HIM) and liquid metal alloy ion source focus ion beam (LMAIS-FIB) are used to locally irradiate the (-201)-oriented β-Ga₂O₃ with neon and metal ions, respectively. Spatially resolved texture analysis was performed by electron backscatter diffraction (EBSD) and confirmed the β to γ phase transition. Transmission electron microscopy (TEM) was also performed to observe the depth profile and interface between two polymorphs. We see a certain fluence where the β to γ-Ga₂O₃ phase transition is completed for both neon (figure 1). Using Positron Annihilation Lifetime Spectroscopy (PALS) and Doppler Broadening Variable Energy Positron Annihilation Spectroscopy (DB-VEPAS) on broad-beam neon irradiated samples, we observed a reduction in defect concentration and relaxation of accumulated defects after the phase transition. Moreover, a sharp interface between two phases makes local noble gas FIB implantation a promising method to fabricate double polymorph Ga₂O₃ nanostructures.

U. Bektas¹, P. Chekhonin², R. Hübner¹, N. Klingner¹, G. Hlawacek<sup>1

1</sup>Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328, Dresden, Germany
²Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, 01328, Dresden, Germany