Structural transition and recovery of Ge implanted β-Ga2O3

Ion implantation-induced effects were studied in Ge implanted beta-Ga2O3 with the fluence and energy of 3x10(13)cm(-2)/60keV, 5x10(13)cm(-2)/100keV, and 7x10(13)cm(-2)/200keV 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 similar to 130nm 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 kappa phase, indicating an implantation-induced phase transition from beta to kappa-Ga2O3. Post-implantation annealing at 1150 degrees C for 60 s under the O-2 atmosphere led to a back transformation of kappa to beta; however, an similar to 17nm damage zone remained at the sample surface. Despite the back transformation from kappa to beta 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 (similar to 130nm) 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 beta-Ga2O3 and the related recovery mechanism, opening a window toward building a reliable device for targeted applications.