All ETDs from UAB

Advisory Committee Chair

Mary E Zvanut

Advisory Committee Members

Shane A Catledge

Cheng-Chien Chen

Sarit Dhar

Vladimir V Fedorov

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences


Beta-gallium oxide (β-Ga2O3) is an ultrawide bandgap semiconductor with promising applications in high-power electronics. The ability of Ga2O3 to be grown from the melt will enable the production of potentially low-cost native substrates, unlike competing materials like GaN and diamond. To fully develop the potential of Ga2O3 as a material for device application, it is critical to have a thorough understanding and control of defects, as well as knowledge of the defect’s thermodynamic transition energy or defect level. This work investigates Fe or Mg, which are used to make semi-insulating Ga2O3 substrates useful for device fabrication, and determines the defect levels and optical transitions for Fe and Mg by using photoinduced electron paramagnetic resonance (photo- EPR). Steady-state and time-dependent photo-EPR measurements were performed on Fedoped and Mg-doped β-Ga2O3 crystals. Optical transitions at 1.2 eV, 2.3 eV, and 3.0 eV were observed for Fe3+ whereas for Mg0 two transitions were observed, one at 1.6 eV and the other greater than 2.5 eV. The 1.2 eV absorption is intrinsic to Fe in Ga2O3. An optical cross section spectrum obtained from time-dependence of Fe3+, when compared with a model that incorporates electron-lattice interaction, yields the Fe2+/3+ level of 0.65 ± 0.1 eV below the conduction band minimum. The other two transitions are indirect transitions of Fe. While the 2.3 eV absorption is predominantly due to Ir, the 3.0 eV absorption involves iv vacancy-related defects. For Mg0, the 1.6 eV transition occurs due to photoexcitation of electron from valence band to the defect. An optical cross section analysis similar to the case of Fe yields the Mg-/0 level of 1.2 eV above the valence band maximum. This is the first experimental demonstration of Mg-/0 level that is consistent with theoretical calculations. The transition greater than 2.5 eV of Mg0 is related to photoexcitation involving other defects. In summary, this work demonstrates Fe2+/3+ and Mg-/0 levels lie deeper than 0.6 eV from band edges, suggesting Fe or Mg is a deep acceptor and can produce semi-insulating Ga2O3 substrates. Moreover, the work illustrates a methodology for an interpretation of optically induced phenomena.