Deep Donor Behavior of Iron in β-Ga₂O₃ Crystals: Establishing the Fe^4+/3+ Level

Timothy D. Gustafson, Air Force Institute of Technology
Christopher A. Lenyk, Air Force Institute of Technology
Larry E. Halliburton, West Virginia University
Nancy C. Giles, Air Force Institute of Technology

© 2020 Authors.

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Plain-text title: Deep donor behavior of iron in β-Ga 2 O 3 crystals: Establishing the Fe 4+/3+ level

Abstract

The Fe^4+/3+ donor level is experimentally determined to be 0.70 eV (±0.05 eV) above the valence band maximum in β-Ga₂O₃. Electron paramagnetic resonance (EPR) is used to monitor Fe³⁺ ions that are unintentionally present in an Mg-doped β-Ga₂O₃ crystal (with a low Fermi level). For temperatures near 255 K, exposure to 325 nm laser light converts a portion of the Fe³⁺ ions to Fe⁴⁺ and Fe²⁺ ions and, at the same time, forms neutral magnesium acceptors (Mg⁰_Ga) and neutral Ir donors (Ir³⁺). After removing the light, the intensity of the Fe³⁺ EPR spectrum has a significant additional decrease as holes thermally released to the valence band from rapidly decaying neutral Mg acceptors are trapped at Fe³⁺ ions and form even more Fe4+ ions. This demonstrates that the Mg^0/- acceptor level, near 0.65 eV, is closer to the valence band than the Fe^4+/3+ level. Following the fast initial post-light decrease, the Fe³⁺ spectrum then slowly recovers as Fe⁴⁺ ions are destroyed by electrons thermally excited from the valence band. An activation energy for the thermal decay of the Fe⁴⁺ donors, and thus a value for the Fe^4+/3+ level, is obtained from the analysis of five Fe³⁺ isothermal recovery curves taken from the Mg-doped crystal between 250 and 270 K. A first-order kinetics model is used, as minimal retrapping is observed. In separate experiments, EPR shows that Fe⁴⁺ ions are also produced in an Fe-doped β-Ga₂O₃ crystal (without Mg acceptors) during exposures to laser light at temperatures near 255 K. Abstract © 2020 Author(s).