Defect Analysis of the <i>β</i> – to <i>γ</i> –Ga ₂ O ₃ Phase Transition

Abstract This study investigates the ion irradiation induced phase transition in gallium oxide (Ga 2 O 3 ) from the to the phase, the role of defects during the transformation, and the quality of the resulting crystal structure. Using a multi‐method analysis approach including X‐ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering spectrometry in channeling mode (RBS/c), Doppler broadening variable energy positron annihilation spectroscopy (DB‐VEPAS), and variable energy positron annihilation lifetime spectroscopy (VEPALS) supported by density functional theory (DFT) calculations, defects at all the relevant stages of the phase transition are characterized. A reduction in backscattering yield is observed in RBS/c spectra after the transition to the phase. This goes hand in hand with a significant decrease in the positron trapping center density due to generation of embedded vacancies intrinsic for the – but too shallow in order to trap positrons. A comparison of the observed positron lifetime of –Ga 2 O 3 with different theoretical models shows good agreement with the three‐site phase approach. A characteristic increase in the effective positron diffusion length and the positron lifetime at the transition point from – to – enables visualization of the phase transition with positrons for the first time. Moreover, a subsequent reduction of these quantities with increasing irradiation fluence is observed, which attributes to further evolution of the – and changes in the gallium vacancy density as well as relative occupation in the crystal lattice.