Abstract Body: β -Ga2O3 has attracted considerable technological and scientific interest due to its ultra-wide ~ 4.8 eV band gap and its extremely high projected ~ 8 MV/cm breakdown field, both of which can advance high-power and high-speed electronics. However, to reach the full potential of these applications, an understanding and control of electrically - active native point defects and impurities in β -Ga2O3 is needed. Besides their contribution to shallow dopants, deep levels of such extrinsic states can compensate free carriers and have a major impact on their recombination and transport, and possibly their ultimate breakdown voltage strength. Luminescence studies [1-3] have identified commonly observed emissions at 2.5 eV, 2.8 eV, 3.0 eV, 3.5 eV and 3.8 eV, some of whose nature can be related to native defects. The deep level defect nature of extrinsic impurities such as Ir in β -Ga2O3 is of interest since high quality single crystal growth techniques such as edge-defined film-fed growth (EFG) make use of iridium dies and crucibles and because large EFG crystals can be grown with quality that is suitable for technological applications. Hence, the impact of Ir in β -Ga2O3 is of both scientific and practical concern. We used depth-resolved cathodoluminescence spectroscopy (DRCLS) and surface photovoltage spectroscopy (SPS) to explore the nature of optical transitions at Ir- Tamura Corp. (010) UID EFG interfaces. Low-kV e-beam excitation through 25 nm-thick, e-beam-deposited Ir-Ga2O3 diodes provided DRCL spectra with near-nm depth resolution. Near - surface and bulk DRCLS of adjacent bare Ga2O3 reveals a prominent ~3.2 eV emission similar to a photoluminescence/cathodoluminescence feature reported previously [4,5], while our SPS identifies a similar transition located 3.15 eV± 0.1 eV below the conduction band. These results are consistent with various theoretical and experimental studies that attribute the ~3.2 eV emission to recombination involving self-trapped holes. Near-nm scale DRCLS at the Ir-Ga2O3 interface shows the emergence of 2.1 eV and 2.6 eV features, which is consistent with transitions associated with the complementary IrGa(II) (0/+) and IrGa(II) (+/0) levels predicted theoretically [6]. The ~3.2 eV emission peak energy maximum also shifts downward towards the Ir-Ga2O3 interface, which correlates with the emergence of a sharp ~2.9 eV emission that can possibly be identified with a IrGa(I) charge state transition. These measurements provide a distinction as well as possible interplay between deep level emission due to Ir impurities and possible self-trapped polarons that can introduce deep level recombination that affect free carrier transport, density, and dielectric breakdown. These results also suggest that Ir is readily incorporated into the Ga2O3 lattice and can produce a major luminescence feature that may produce significant free carrier recombination and compensation. Research efforts are currently underway to perform rapid-thermal annealing on the Ir-deposited sample to determine the activation energy and diffusion coefficient for Ir in Ga2O3. DNR, MSH, and LJB gratefully acknowledge AFOSR Grant No. FA9550-18-1-0066 (Ali Sayir). [1] H. Gao et al., Appl. Phys. Lett. 112, 242102 (2018). [2] H. Gao et al., J. Phys. D: Appl. Phys. 53 465102 (2020). [3] Y. Wang et al., Sci. Rep. 8, 18075 (2018). [4] S. Yamaoka et al., Physical Review B 95, 094304 (2017). [5] T. Onuma et al., Appl. Phys. Lett. 103, 041910 (2013). [6] J.R. Ritter et al., Appl. Phys. Lett. 113, 052101 (2018).

Deep Levels and Self-Trapped Excitons at Iridium/Edge-Fed Grown β-Ga2O3 Interfaces

U: Diamond, Gallium Oxide and Related Materials

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Deep Levels and Self-Trapped Excitons at Iridium/Edge-Fed Grown β-Ga2O3 Interfaces

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