Gallium vacancy formation in oxygen annealed β-Ga2O3

In this study, the formation and character of gallium vacancies (V-Ga) and their complexes in near surface and bulk regions of single crystal beta-Ga2O3 were explored using unintentionally doped single crystals grown by the Czochralski method. As-grown and O-2 annealed (up to 1550 degrees C) samples were investigated using positron annihilation spectroscopy (PAS) to study the top 0.05-6 mu m, and also current-voltage measurements and infrared (IR) spectroscopy, with hydrogenated samples to probe V-Ga, to study the bulk. After annealing in O-2 > 1000 degrees C, the beta-Ga2O3 resistivity begins increasing, up to similar to 10(9) omega cm for 1550 degrees C treatment, with the top 0.5 mm being many orders of magnitude more resistive. PAS measurements of the top 6 mu m (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. V-Ga are present in the bulk after growth, but considerable changes occur upon annealing at a temperature approximate to 1000 degrees C, where L and S decrease simultaneously, suggesting an increasing defect concentration (L) but a decreasing defect volume (S). Annealing at a temperature approximate to 1400 degrees C increases S again, showing an increasing volume concentration of V-Ga, with IR absorption showing a large signature of V-Ga-2H, indicative of increased V-Ga formation that was not present when annealing at a temperature approximate to 1000 degrees C. These results suggest that defect changes from annealing in oxygen are depth dependent, and that V-Ga configuration may not be the same near the oxygen-exposed surface of the sample and in the bulk.

Automated summary

This study explores the formation and character of gallium vacancies (V-Ga) and their complexes in near surface and bulk regions of single crystal beta-Ga2O3. The results suggest that defect changes from annealing in oxygen are depth dependent, and the configuration of V-Ga may differ near the oxygen-exposed surface of the sample and in the bulk.