Date of Award

8-23-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

Nancy C. Giles, PhD

Abstract

Electron paramagnetic resonance (EPR), Fourier-Transform Infrared spectroscopy (FTIR), photoluminescence (PL), thermoluminescence (TL), and wavelength-dependent TL are used to identify and characterize point defects in lithium gallate and β-gallium oxide doped with Mg and Fe acceptor impurities single crystals. EPR investigations of LiGaO2 identify fundamental intrinsic cation defects lithium (V−Li) and gallium (V2−Ga) vacancies. The defects’ principle g values are found through angular dependence studies and atomic-scale models for these new defects are proposed. Thermoluminescence measurements estimate the activation energy of lithium vacancies at Ea = 1.05 eV and gallium vacancies at Ea > 2 eV below the conduction band minimum. Mg and Fe doped β-Ga2O3 crystals are investigated with EPR and FTIR and concentrations of Ir4+ ions greater than 1 × 1018 cm3 are observed. The source of the unintentional deep iridium donors is the crucible used to grow the crystal. In the Mg-doped crystals, the Ir4+ ions provide compensation for the singly ionized Mg acceptors contributing to the difficulties in producing p-type behavior in bulk single crystals. A large spin-orbit coupling causes Ir4+ ions to have a low-spin (5d5, S = 1/2) ground state. The Ir4+ ions have an infrared absorption band representing a d − d transition within the t2g orbitals. Using these same techniques the Fe2+/3+ level in Fe-doped β-Ga2O3 crystals is determined. With these noncontact spectroscopy methods, a value of 0.83 ± 0.04 eV below the conduction band is obtained for this level. These results clearly establish that the E2 deep level observed in DLTS experiments is due to the thermal release of electrons from Fe2+ ions.

AFIT Designator

AFIT-ENP-DS-19-S-023

DTIC Accession Number

AD1084594

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