Gallium vacancy formation in oxygen annealed β-Ga2O3

Abstract

In this study, the formation and character of gallium vacancies (VGa) and their complexes in near surface and bulk regions of single crystal β-Ga2O3 were explored using unintentionally doped single crystals grown by the Czochralski method. As-grown and O2 annealed (up to 1550 °C) samples were investigated using positron annihilation spectroscopy (PAS) to study the top 0.05–6 μm, and also current–voltage measurements and infrared (IR) spectroscopy, with hydrogenated samples to probe VGa, to study the bulk. After annealing in O2 > 1000 °C, the β-Ga2O3 resistivity begins increasing, up to ∼109 Ω cm for 1550 °C treatment, with the top 0.5 mm being many orders of magnitude more resistive. PAS measurements of the top 6 μm (S values) and very near surface 200 nm (diffusion length, L) indicate differential behavior as a function of peak annealing temperature. At least four temperature regimes of behavior are described. VGa are present in the bulk after growth, but considerable changes occur upon annealing at a temperature ≈1000 °C, where L and S decrease simultaneously, suggesting an increasing defect concentration (L) but a decreasing defect volume (S). Annealing at a temperature ≈1400 °C increases S again, showing an increasing volume concentration of VGa, with IR absorption showing a large signature of VGa-2H, indicative of increased VGa formation that was not present when annealing at a temperature ≈1000 °C. These results suggest that defect changes from annealing in oxygen are depth dependent, and that VGa configuration may not be the same near the oxygen-exposed surface of the sample and in the bulk.