Cobalt as a promising dopant for producing semi-insulating β-Ga2O3 crystals: Charge state transition levels from experiment and theory

Optical absorption and photoconductivity measurements of Co-doped beta-Ga2O3 crystals reveal the photon energies of optically excited charge transfer between the Co related deep levels and the conduction or valence band. The corresponding photoionization cross sections are fitted by a phenomenological model considering electron-phonon coupling. The obtained fitting parameters: thermal ionization (zero-phonon transition) energy, Franck-Condon shift, and effective phonon energy are compared with corresponding values predicted by first principle calculations based on density functional theory. A (+/0) donor level similar to 0.85 eV above the valence band maximum and a (0/-) acceptor level similar to 2.1 eV below the conduction band minimum are consistently derived. Temperature-dependent electrical resistivity measurement at elevated temperatures (up to 1000 K) yields a thermal activation energy of 2.1 +/- 0.1 eV, consistent with the position of the Co acceptor level. Furthermore, the results show that Co doping is promising for producing semi-insulating beta-Ga2O3 crystals. (C) 2022 Author(s).

Automated summary

Optical absorption and photoconductivity measurements of Co-doped beta-Ga2O3 crystals reveal the photon energies of optically excited charge transfer between the Co related deep levels and the conduction or valence band. The results show that Co doping is promising for producing semi-insulating beta-Ga2O3 crystals, with consistent thermal activation energy of 2.1 +/- 0.1 eV for the Co acceptor level.