Effects of hydrogen plasma treatment condition on electrical properties of β-Ga₂O₃

The effects of hydrogen or deuterium plasma treatment at 330°C on electrical properties and deep trap spectra of n-type β-Ga₂O₃ films grown by halide vapor phase epitaxy on native n⁺ substrates are reported. Under plasma treatment conditions giving rise to higher energy ions (280 eV), hydrogen penetrates into the HVPE films and fully compensates or passivates shallow donors to ∼2 μm from the surface. The Fermi level in this high-resistivity layer is pinned by electron traps near E_c-1 eV (E3 traps) also present in the starting material. Annealing at 450°C shifts the pinning position to another dominant deep trap in the starting material, the E2^∗ traps near E_c-0.75 eV. Subsequent annealing at 550°C almost fully restores the electrical properties. By sharp contrast, plasma treatment under conditions of low energy ions (35eV) severely reduced hydrogen incorporation and only slightly increased the near-surface donor concentration. The observed differences are discussed under the assumption that hydrogen is introduced in the form of isolated acceptor interstitials with the charge transfer level near E_c-0.5 eV in the first case, but as a donor with level inside the conduction band in the second case as proposed by recent theoretical calculations.