Impact of proton irradiation on conductivity and deep level defects in β-Ga 2 O 3

Abstract

Single crystalline bulk and epitaxially grown gallium oxide (β-Ga 2 O 3 ) was irradiated by 0.6 and 1.9 MeV protons to doses ranging from 5 × 10 9 to 6 × 10 14 cm −2 in order to study the impact on charge carrier concentration and electrically active defects. Samples irradiated to doses at or above 2 × 10 13 cm −2 showed a complete removal of free charge carriers in their as-irradiated state, whereas little or no influence was observed below doses of 6 × 10 12 cm −2 . From measurements at elevated temperatures, a thermally activated recovery process is seen for the charge carriers, where the activation energy for recovery follow a second-order kinetics with an activation energy of ∼1.2 eV. Combining the experimental results with hybrid functional calculations, we propose that the charge carrier removal can be explained by Fermi-level pinning far from the conduction band minimum (CBM) due to gallium interstitials (Ga i ), vacancies (V Ga ), and antisites (Ga O ), while migration and subsequent passivation of V Ga via hydrogen-derived or V O defects may be responsible for the recovery. Following the recovery, deep level transient spectroscopy (DLTS) reveals generation of two deep levels, with energy positions around 0.75 and 1.4 eV below the CBM. Of these two levels, the latter is observed to disappear after the initial DLTS measurements, while the concentration of the former increases. We discuss candidate possibilities and suggest that the origins of these levels are more likely due to a defect complex than an isolated point defect.