Creation of shallow donor states in hydrogen plasma exposed undoped α-Ga2O3

High concentrations, 10¹⁹ cm⁻³, of shallow donors are created in initially semi-insulating α-Ga₂O₃ grown on sapphire by Halide Vapor Phase Epitaxy (HVPE) after hydrogen plasma exposure. H-plasma treatment for 0.5 h at 330 °C renders the α-Ga₂O₃ films highly conducting, with shallow donors attributed to interstitial hydrogen. There is also persistent photo capacitance to 400 K, due to the presence of a high density (10¹⁸ cm⁻³) of deep acceptors with optical ionization threshold of 2 eV with a barrier for capture of electrons. These centers are ascribed to Ga vacancy complexes with hydrogen. The top layer of about 20 nm of the Ga₂O₃ has a high density of these acceptors originating from surface damage created by high energy H ions. Annealing to 723 K leads to partial recovery of the initial properties, but the films retain about 10¹⁶ cm⁻³ shallow donors and some remnant centers giving rise to persistent conductivity. The deep trap spectra show electron traps at E_c-0.24 eV, E_c-0.82 eV, E_c-1.2 eV and hole-trap-like signals due to centers with activation energy 0.2 eV and 0.9 eV. The Ga₂O₃ after annealing exhibits low dark current and a high gain in Electron Beam Induced Current measurements. The prospects of using highly conducting hydrogenated films for low temperature fabrication of Ohmic contacts and of hydrogen treated and annealed films for use in high responsivity solar-blind photodetectors are discussed.