madsei

• Ingebrigtsen, Mads Eide; Kuznetsov, Andrej; Svensson, Bengt Gunnar; Alfieri, Giovanni; Mihaila, Andrei & Vines, Lasse (2019). Generation and metastability of deep level states in β-Ga2O3 exposed to reverse bias at elevated temperatures. Journal of Applied Physics. ISSN 0021-8979. 125(18), p. 185706-7–185706-1. doi: 10.1063/1.5088655. Full text in Research Archive Show summary

  An intriguing phenomenon of electrically active defect generation is observed in homoepitaxial β-Ga2O3 films exposed to reverse bias at elevated temperatures. In particular, heating samples up to 675 K in the course of deep level transient spectroscopy measurements, i.e., with the reverse bias and voltage pulsing applied, resulted in the generation of three new levels at ∼1, ∼1.5, and ∼2 eV below the conduction band edge (labeled as E3*, E5, and E6). The corresponding defects exhibit different thermal stabilities; E5 and E6 show stability, while E3* demonstrates a remarkable metastability—it can be generated, annealed out, and regenerated in the course of sequential temperature cycles. Combining a number of annealing tests and using different types of epitaxial materials, the levels were systematically investigated, and the most credible scenario behind the phenomenon is the evolution of already existing defect configurations provoked by the applied temperature and bias.

• Ingebrigtsen, Mads Eide; Kuznetsov, Andrej; Svensson, Bengt Gunnar; Alfieri, Giovanni; Mihaila, Andrei & Badstübner, U. [Show all 9 contributors for this article] (2019). Impact of proton irradiation on conductivity and deep level defects in β-Ga2O3. APL Materials. 7(2), p. 022510-1–022510-10. doi: 10.1063/1.5054826. Full text in Research Archive Show summary

  Single crystalline bulk and epitaxially grown gallium oxide (β–Ga2O3) was irradiated by 0.6 and 1.9 MeV protons to doses ranging from 5 × 109 to 6 × 1014 cm−2 in order to study the impact on charge carrier concentration and electrically active defects. Samples irradiated to doses at or above 2 × 1013 cm−2 showed a complete removal of free charge carriers in their as-irradiated state, whereas little or no influence was observed below doses of 6 × 1012 cm−2. From measurements at elevated temperatures, a thermally activated recovery process is seen for the charge carriers, where the activation energy for recovery follow a second-order kinetics with an activation energy of ∼1.2 eV. Combining the experimental results with hybrid functional calculations, we propose that the charge carrier removal can be explained by Fermi-level pinning far from the conduction band minimum (CBM) due to gallium interstitials (Gai), vacancies (VGa), and antisites (GaO), while migration and subsequent passivation of VGa via hydrogen-derived or VO defects may be responsible for the recovery. Following the recovery, deep level transient spectroscopy (DLTS) reveals generation of two deep levels, with energy positions around 0.75 and 1.4 eV below the CBM. Of these two levels, the latter is observed to disappear after the initial DLTS measurements, while the concentration of the former increases. We discuss candidate possibilities and suggest that the origins of these levels are more likely due to a defect complex than an isolated point defect.

• Ingebrigtsen, Mads Eide; Varley, J.B.; Kuznetsov, Andrej; Svensson, Bengt Gunnar; Alfieri, Giovanni & Mihaila, A. [Show all 8 contributors for this article] (2018). Iron and intrinsic deep level states in Ga2O3. Applied Physics Letters. ISSN 0003-6951. 112(4). doi: 10.1063/1.5020134. Full text in Research Archive Show summary

  Using a combination of deep level transient spectroscopy, secondary ion mass spectrometry, proton irradiation, and hybrid functional calculations, we identify two similar deep levels that are associated with Fe impurities and intrinsic defects in bulk crystals and molecular beam epitaxy and hydride vapor phase epitaxi-grown epilayers of β-Ga2O3. First, our results indicate that FeGa, and not an intrinsic defect, acts as the deep acceptor responsible for the often dominating E2 level at ∼0.78 eV below the conduction band minimum. Second, by provoking additional intrinsic defect generation via proton irradiation, we identified the emergence of a new level, labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2* are found to be consistent with its intrinsic origin. As such, contradictory opinions of a long standing literature debate on either extrinsic or intrinsic origin of the deep acceptor in question converge accounting for possible contributions from E2 and E2* in different experimental conditions.

• Ingebrigtsen, Mads Eide; Vines, Lasse; Alfieri, G; Mihaila, A.; Badstübner, U. & Svensson, Bengt Gunnar [Show all 7 contributors for this article] (2017). Bulk β-Ga2O3 with (010) and (201) surface orientation: Schottky contacts and point defects. Materials Science Forum. ISSN 0255-5476. 897 MSF, p. 755–758. doi: 10.4028/www.scientific.net/MSF.897.755. Full text in Research Archive Show summary

  Electrical properties of Schottky contacts of high work-function metals (Pd, Au, and Ni) on (010) and (201) oriented β-Ga2O3 were investigated. Current-voltage characteristics reveal that all the contacts exhibit high rectifying behavior with ideality factors as low as 1.04. However, the reverse leakage currents were lower in the (010) samples compared to the (201) ones. Thermal admittance spectroscopy confirms a main charge carrier level to be at ~0.15 eV below the conduction band edge (Ec). Secondary ion mass spectrometry indicates that Si may be responsible for this donor level. Deep level transient spectroscopy reveals four levels (E1-E4) in the upper part of the band gap, with the corresponding energy level positions at 0.56, 0.76, 1.01, and 1.48 eV below Ec.

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• 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
• Vines, Lasse; Ingebrigtsen, Mads Eide; Alfieri, Giovanni; Mihaila, Andrei; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2017). Deep level defects in bulk and epi-grown β-Ga2O3. Full text in Research Archive
• Ingebrigtsen, Mads Eide; Vines, Lasse; Alfieri, Giovanni; Mihaila, Andrei; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2017). Donor states and deep levels in bulk and epitaxial β-Ga2O3. Full text in Research Archive
• Frodason, Ymir Kalmann; Bergum, Kristin; Sky, Thomas Neset; Ingebrigtsen, Mads Eide; Borgersen, Jon & Ellingsen, Josef Gert Åsheim [Show all 8 contributors for this article] (2017). MiNa-Lab tour highlighting LENS activities. Full text in Research Archive
• Bergum, Kristin; Borgersen, Jon Arthur; Ellingsen, Josef Gert Åsheim; Hallén, Anders; Ingebrigtsen, Mads Eide & Kuznetsov, Andrej (2017). Omvisning MiNaLab, Slemdal skole 4. trinn. Full text in Research Archive
• Bergum, Kristin; Borgersen, Jon Arthur; Ellingsen, Josef Gert Åsheim; Frodason, Ymir Kalmann; Galeckas, Augustinas & Ingebrigtsen, Mads Eide [Show all 8 contributors for this article] (2017). Omvisning MiNaLab. Full text in Research Archive
• Ingebrigtsen, Mads Eide (2019). Electrical characterization and identification of deep levels in beta-Ga2O3. Universitetet i Oslo. Full text in Research Archive

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