Positron Annihilation Spectroscopy of Vacancy Type Defects in Electron Irradiated β-Ga2O3

Positron annihilation spectroscopy is applied to high-quality beta-Ga2O3 [010] oriented 5 mu m thick epilayer before and after electron irradiation to calculate absolute vacancy concentrations. Room temperature irradiated is carried out with 2.5 MeV electrons to a dose of 1.9 x 1019 cm-2 to generate high concentrations of vacancies. Both oxygen and gallium vacancies are generated. The vacancy-sensitive depth-dependent S-parameter and the positron diffusion length were measured to determine vacancy concentrations. The positron diffusion length dropped from 101 +/- 2 nm to 47 +/- 2 nm while the S-value in the epilayer rose 2.1 +/- 0.3%. The positron annihilation spectroscopies (PAS) results on the irradiated film, in comparison with unirradiated as-grown high-quality bulk single crystals, are used to obtain for the first time a quantitative estimate of the defect concentration from the S-parameter for various samples. The -3 charge state of gallium vacancies is taken into account. PAS results on irradiated silicon are shown for contrast, to illustrate the complications in beta-Ga2O3 introduced by a significant orientation dependence and, likely, the presence of hydrogen.