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• Borgersen, Jon; Karsthof, Robert Michael; Rønning, Vegard; Vines, Lasse; Wenckstern, Holger Von & Grundmann, Marius [Show all 8 contributors for this article] (2023). Origin of enhanced conductivity in low dose ion irradiated oxides. AIP Advances. 13(1), p. 015211-1–015211-5. doi: 10.1063/5.0134699. Full text in Research Archive Show summary

  Significant resistivity variations have previously been observed in oxides subjected to relatively low ion irradiation doses, nominally insufficient to generate the amount of bulk defects needed to explain the phenomena. In an effort to unveil the underlying mechanisms, we performed a systematic comparative study of the resistivity evolution in In 2 O 3 -based oxides as a function of low ion doses and ultraviolet (UV) illumination, observing striking correlations. Specifically, we found that irradiation with ∼3 × 10 12  Si/cm 2 and ∼18 h UV exposure result in similar resistivity drops, interpreted in terms of irradiation/illumination assisted desorption of oxygen containing species from the surface. This was further proven by post-irradiation exposure of one of the samples to an oxygen atmosphere partially restoring the resistivity. Combining the present results with literature data, we conclude that the radiation tolerance of In 2 O 3 -based and similar oxides depends on the surface charge modifications, individual defect contributions, and contributions from defect complexes at low, intermediate, and high doses, respectively.

• Zimmermann, Christian; Rønning, Vegard; Frodason, Ymir Kalmann; Bobal, Viktor; Varley, Joel B & Vines, Lasse (2020). Primary intrinsic defects and their charge transition levels in beta-Ga2O3. PHYSICAL REVIEW MATERIALS. 4(7). doi: 10.1103/PhysRevMaterials.4.074605. Full text in Research Archive Show summary

  A steady-state photocapacitance (SSPC) setup directly connected to the beamline of a MeV ion implanter is utilized to study primary intrinsic defects in β–Ga2O3 generated by He implantation at cryogenic temperatures (120 K). At low temperatures, the migration of defects is suppressed, and hence the generation of primary intrinsic defects is expected to prevail. SSPC measurements reveal defect-related optical transitions in halide vapor-phase epitaxy (HVPE) -grown β–Ga2O3 thin films with onset energies at 1.3 (T1), 1.7 (T2), 1.9 (T3), 2.6 (T4), 3.7 (T5), and 4.2 eV (T6). T2, T4, T5, and T6 were observed in as-received HVPE-grown β–Ga2O3 thin films, whereby T2 is only sporadically observed. The introduction rates for T3, T4, as well as T6 indicate an origin related to primary intrinsic defects. Notably, T1 and T3 are only observed after He implantation at cryogenic temperatures. Hybrid-functional calculations were performed to estimate the optical absorption cross-section spectra for the gallium (Gai) and oxygen (Oi) interstitials as well as the corresponding vacancies (VGa and VO, respectively), and compared with the measured onsets for optical absorption found by SSPC measurements. Indeed, we propose T3 to be associated with Ga(+/+2)i and/or V(−3/−2)GaI, while T4 is suggested to be related to V(0/+)OK (K=I, II, III) and/or V(−3/−2)GaII. Additionally, several further charge-state transition levels associated with VGaI and VGaII may contribute to T4 and T6. We further studied the kinetics of the defects created with He implantation by exposing the sample to room temperature. The kinetics observed for T3 and T4 further support the proposed assignments of the corresponding defect signatures.

• Zimmermann, Christian; Frodason, Ymir Kalmann; Rønning, Vegard; Varley, Joel B & Vines, Lasse (2020). Combining steady-state photo-capacitance spectra with first-principles calculations: the case of Fe and Ti in β-Ga2O3. New Journal of Physics. 22. doi: 10.1088/1367-2630/ab8e5b. Full text in Research Archive

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• Zimmermann, Christian; Frodason, Ymir Kalmann; Varley, Joel Basile; Verhoeven, Espen Førdestrøm; Rønning, Vegard & Weiser, Philip Michael [Show all 15 contributors for this article] (2021). Identification of Fe-, Ti- and H-related Charge-state Transition Levels in β-Ga2O3. Full text in Research Archive
• Vines, Lasse; Ingebrigtsen, Mads Eide; Zimmermann, Christian; Rønning, Vegard & Kuznetsov, Andrej (2019). Electrically Active Defects in β-Ga2O3. Full text in Research Archive
• Bathen, Marianne Etzelmüller; Ingebrigtsen, Mads Eide; Olsen, Vegard Skiftestad; Rønning, Vegard & Vines, Lasse (2018). Omvisning for studieprogrammene FA og ELITE. Full text in Research Archive

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