Proton damage effects in double polymorph γ/β-Ga2O3 diodes

Abstract

Double polymorph γ/β-Ga₂O₃ structures remain crystalline upon unprecedentedly high crystal disorder levels where other semiconductors lose their long-range symmetry and, eventually, become amorphous. However, it is unclear if this radiation tolerance translates to device-like operation, where much lower levels of damage degrade the performance. In this work, we fabricated conducting double polymorph γ/β-Ga₂O₃ structures using ion implantation and subsequent hydrogenation of the top γ-Ga₂O₃ layer, instead of conventional impurity doping which is limited by γ-Ga₂O₃ stability tradeoffs. While not a direct comparison, these structures exhibited much higher radiation tolerance compared to conventional Schottky diodes made of β-Ga₂O₃. Specifically, using 1.1 MeV proton irradiation at fluences of 10¹⁴–10¹⁵ cm⁻², conventional β-Ga₂O₃ diodes became unfunctional, while double polymorph γ/β-Ga₂O₃ diodes remained operational. The centers supplying electrons in γ-Ga₂O₃ were characterized by prominent DX-like persistent photocapacitance. For samples implanted with Ga⁺ and Si⁺ to produce the β → γ transition, annealed at 600 °C and plasma hydrogenated, the net donor concentration was ∼10¹² cm⁻³, with dominant electron traps near E_C − 0.65–0.7 eV and photocapacitance and photocurrent spectra determined by deep acceptors with optical ionization thresholds 1.3 eV, 2 eV, 2.3 eV and 2.8 eV. Irradiation with 1 MeV protons increased the net donor density of these conducting γ/β-Ga₂O₃ structures, with carrier creation rates of (1.5–4.4) × 10⁻² cm⁻², in sharp contrast to the carrier removal rates of 150–200 cm⁻¹ under identical conditions in the original β-Ga₂O₃ films.