Crystallization phenomena in β-Ga2O3 investigated by positron annihilation spectroscopy and X-ray diffraction analysis

Samples of single- and polycrystalline β-Ga2O3, undoped and doped with Tb3+ or Dy3+ were investigated by positron lifetime spectroscopy and by X-ray diffraction analysis. The positron annihilation data show that there are more large open-volume defects in the samples sintered at 800 °C than in the samples sintered at higher temperatures (1200 and 1500 °C). Also, intergranular precipitation of second-phase particles (crystallites) of RE3Ga5O12 is suggested to occur in the doped samples sintered at 1200 and 1500 °C, and is confirmed by the X-ray diffraction data. These second-phase crystallites are inclined to precipitate either along grain boundaries or at surfaces of pores. For the samples sintered at 800 °C, most rare earth ions remain in the oxide forms and the second phase of RE3Ga5O12 is not nucleated. This indicates that a sintering temperature of 800 °C may not be high enough to trigger the growth of the second phase of RE3Ga5O12.