Structural transition and recovery of Ge implanted β -Ga2O3

Abstract

Ion implantation-induced effects were studied in Ge implanted β-Ga2O3 with the fluence and energy of 3 × 1013 cm−2/60 keV, 5 × 1013 cm−2/100 keV, and 7 × 1013 cm−2/200 keV using analytical electron microscopy via scanning/transmission electron microscopy, electron energy loss spectroscopy, and precession electron diffraction via TopSpin. Imaging shows an isolated band of damage after Ge implantation, which extends ∼130 nm from the sample surface and corresponds to the projected range of the ions. Electron diffraction demonstrates that the entirety of the damage band is the κ phase, indicating an implantation-induced phase transition from β to κ-Ga2O3. Post-implantation annealing at 1150 °C for 60 s under the O2 atmosphere led to a back transformation of κ to β; however, an ∼17 nm damage zone remained at the sample surface. Despite the back transformation from κ to β with annealing, O K-edge spectra show changes in the fine structure between the pristine, implanted, and implanted-annealed samples, and topspin strain analysis shows a change in strain between the two samples. These data indicate differences in the electronic/chemical structure, where the change of the oxygen environment extended beyond the implantation zone (∼130 nm) due to the diffusion of Ge into the bulk material, which, in turn, causes a tensile strain of 0.5%. This work provides a foundation for understanding of the effects of ion implantation on defect/phase evolution in β-Ga2O3 and the related recovery mechanism, opening a window toward building a reliable device for targeted applications.

Activation energy of silicon diffusion in gallium oxide: Roles of the mediating defects charge states and phase modification

“…Importantly, the change in the conditions for the VGa generation at the surface may be potentially induced not only by different atmospheres, but also by modifying the surface. Indeed, recently, ion-beam-induced phase transformations of -Ga2O3 to phase were reported [15,22]. In particular, Azarov et al [15] have demonstrated that a certain threshold in the density of the radiation damage may be reached to enable the to- phase transformation.…”

“…In relation to the present Si diffusion study, the conditions for the Si implants (as shown in Fig. 1) were selected to be under this threshold as compared with the heavier ion mass Ni, Ga, Ge, or Au implants, known to result into the -to- phase transformation in the near surface volume [15,22]. In the present work, in order to modify the Si diffusion conditions we fabricated pre-existing -phase surface layer on the top of the bulk -Ga2O3 wafer where Si diffused.…”

“…surface. However, κ-phase is metastable and recrystallizes back to -Ga2O3 rapidly upon annealing [15,22], so that it affects the diffusion process only at lower temperatures. Notably Ni atoms are much more thermally stable as compared to Si and very little Ni diffusion was detected for the temperature range studied, see Fig.…”

Ion-beam modification of metastable gallium oxide polymorphs

“…An alternative assumption is that the irradiation has induced the (κ) → β phase transition, in analogy with the β → κ transition observed by Anber et al in Ref. 17 . However, a detailed analysis of the new lines positions shows that the deviation from the tabulated values is rather large making this mechanism less probable.…”

“…The question is, whether the appearance of these lines is associated with a phase transformation (see e.g. 17 ) or with the deformation of the (κ)-phase inclusions. To answer this question, the relative change in the interplanar distance ∆d/d has been calculated for the newly emerged lines relative to the nearest preserved lines of the (κ)-phase with indices (002), ( 004) and (006), using the relation 2dsin(θ) = nλ.…”