Generation and metastability of deep level states in β-Ga2O3 exposed to reverse bias at elevated temperatures

Ingebrigtsen, M. E.; Kuznetsov, A. Yu.; Svensson, B. G.; Alfieri, Giovanni; Mihaila, A.; Vines, Lasse

doi:10.1063/1.5088655

“…Notably, E * 2 has also been observed in as-grown β-Ga 2 O 3 thin-films deposited by MBE, and was found to significantly impact the performance of MESFETs comprising these thin-films [98,106]. Recently, it has been reported that a number of defects are created in β-Ga 2 O 3 at elevated temperatures when an electrical field is present inside the material [104]. This finding has great implications for β-Ga 2 O 3 -based devices and their longterm operation.…”

Section: Influence Of Defects On the Electrical Propertiesmentioning

confidence: 98%

“…The active region usually comprises n-type β-Ga 2 O 3 , and thus, defects with charge state transition levels far away from E C are considered to be deep-level defects. Deep-level defects can either be present in as-grown β-Ga 2 O 3 [91,[98][99][100], are created during fabrication [101] or diffuse in from adjacent layers during fabrication as well as operation [98,[102][103][104] (see Fig. 4.1).…”

Section: Monoclinic Gallium Sesquioxidementioning

confidence: 99%

Ti- and Fe-related charge transition levels in β−Ga2O3

Zimmermann

¹

,

Frodason

²

,

Barnard

³

et al. 2020

Applied Physics Letters

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This thesis would not have been possible without the support of many people, and I am eternally grateful for all the support. I hope to see some of you again in the future! The main objective of my PhD project was to study defects in semiconducting oxides within the research project FOXHOUND headed by Prof. Lasse Vines, my main supervisor. I am grateful to Lasse for the opportunity to work on this topic. I have learned much more than I imagined I would when I started. Lasse, you have been a patient and competent supervisor who always took time to answer endless streams of questions. Prof. Truls Norby and Assoc. Prof. Anette Eleonora Gunnaes were co-advisors for my PhD project. I am grateful to Truls for introducing me to the chemist's view on defects and his group FASE/ELCHEM. I am truly sad that I did not get to collaborate more with Anette. I also want to thank Prof. Eduard Monakhov and the late Prof. Bengt Gunnar Svensson. Both were valuable unofficial advisers on my PhD, and helped moving my work along. Most of my work was carried out within the semiconductor physics group at the University of Oslo (LENS), and I would like to thank of all its current and former members for contributing to my work in many ways. There are some people who deserve special thanks. First of all, I am grateful to my long-term office mates Torunn, Sigbjørn and Josef for sharing many conversations and being there for each other. Secondly, I am particularly grateful to all my close collaborators at LENS, and especially Julie, Philip, Ymir, Vegard R., Vegard O., Viktor and Espen. I also want to thank our engineers (Micke, Halvor, Christoph and Viktor) and administrative staff (Marit, Heine and Kristin) for keeping things running! Also, thanks to Ilia, Robert, Vegard R. and Jon for taking care of the needs of the E-Lab and the Online-Setup. I was a co-supervisor for two master students: Vegard R. and Espen. I hope both of them learned something from me, because I did definitely learn from them. I am particularly grateful to Vegard R. for being a large part in building the steady-state photo-capacitance setup used in this work. I also would like to thank all my co-authors from outside of Oslo: Frank from Dresden, Willem, Walter and Danie from Pretoria, Klaus and Zbigniew from Berlin, Antti from Aalto and Joel from California. Special thanks to Willem, Walter and Danie for hosting me in Pretoria and showing me around. Last but not least, I would like to thank my family and my friends for their support!

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“…The position of the Fermi level can have a pronounced influence on defect formation processes via the contribution of the electron chemical potential to defect formation energies [21][22][23]. Particularly, it has been shown that several defect signatures are introduced in the space-charge region of β-Ga 2 O 3 Schottky barrier diodes (SBDs) when the diodes are exposed to elevated temperatures in conjunction with an applied bias voltage, causing a change in the Fermi-level position within the space-charge region [24]. Moreover, hydrogen (H) can play an important role in defect formation because H is expected to be mobile at or slightly above room temperature in β-Ga 2 O 3 , and has been shown to form complexes with various acceptor defects [23,[25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Formation and control of the E2∗ center in implanted β-Ga 2 O 3 by reverse-bias and zero-bias annealing

Zimmermann

¹

,

Verhoeven

²

,

Frodason

³

et al. 2020

J. Phys. D: Appl. Phys.

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Deep-level transient spectroscopy measurements are conducted on β-Ga 2 O 3 thin-films implanted with helium and hydrogen (H) to study the formation of the defect level E 2 ∗ ( E A = 0.71 eV) during heat treatments under an applied reverse-bias voltage (reverse-bias annealing). The formation of E 2 ∗ during reverse-bias annealing is a thermally-activated process exhibiting an activation energy of around 1.0 eV to 1.3 eV, and applying larger reverse-bias voltages during the heat treatment results in a larger concentration of E 2 ∗ . In contrast, heat treatments without an applied reverse-bias voltage (zero-bias annealing) can be used to decrease the E 2 ∗ concentration. The removal of E 2 ∗ is more pronounced if zero-bias anneals are performed in the presence of H. A scenario for the formation of E 2 ∗ is proposed, where the main effect of reverse-bias annealing is an effective change in the Fermi-level position within the space-charge region, and where E 2 ∗ is related to a defect complex involving intrinsic defects that exhibits several different configurations whose relative formation energies depend on the Fermi-level position. One of these configurations gives rise to E 2 ∗ , and is more likely to form if the Fermi-level position is further away from the conduction band edge. The defect complex related to E 2 ∗ can become hydrogenated, and the corresponding hydrogenated complex is likely to form when the Fermi level is close to the conduction band edge. Di-vacancy defects formed by oxygen and gallium vacancies (V O −V G a ) fulfill several of these requirements, and are proposed as potential candidates for E 2 ∗ .

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“…35 and we add E14-16 here in this work. The UID sample shows four majority defects located at For negative majority emission transients, the energy levels obtained from DLTS measurements can vary depending on the electrical field in which the defect sits during the measurement phase of the experiment which in turn changes as a function of built-in and applied bias and doping density 20,30,34,38 . As shown in Fig.2b, the DLTS signals in the UID sample shift toward lower temperature and the asymmetric tails at lower temperature side enlarge for increasing reverse biaseseffects which are more pronounced for the #1 Zr doped sample (Fig.2c).…”

mentioning

confidence: 99%

“…For negative majority emission transients, the energy levels obtained from DLTS measurements can vary depending on the electrical field in which the defect sits during the measurement phase of the experiment which in turn changes as a function of built-in and applied bias and doping density 20,30,34,38 . As shown in Fig.…”

mentioning

confidence: 99%

Defect states and their electric field-enhanced electron thermal emission in heavily Zr-doped β -Ga2O3 crystals

Sun

¹

,

Ooi

²

,

Bhattacharyya

³

et al. 2020

Applied Physics Letters

18

0

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Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (Ec) in Czochralski (CZ) grown unintentionallydoped (UID) and vertical gradient freeze (VGF)-grown Zr-doped -Ga2O3 crystals. In UID crystals with an electron concentration of 10 17 cm-3 , we observe levels at 0.18 eV and 0.46 eV in addition to the previously reported 0.86 (E2) and 1.03 eV (E3) levels. For 10 18 cm-3 Zr-doped Ga2O3, signatures at 0.30 eV (E15) and 0.71 eV (E16) are present. For the highest Zr doping of 510 18 cm-3 , we observe only one signature at 0.59 eV. Electric field-enhanced emission rates are demonstrated via increasing the reverse bias during measurement. The 0.86 eV signature in the UID sample displays phonon-assisted tunneling enhanced thermal emission and is consistent with the widely reported E2 (FeGa) defect. The 0.71 eV (E16) signature in the lower-Zr-doped crystal also exhibits phonon-assisted tunneling emission enhancement. Taking into account that the high doping in the Zr-doped diodes also increases the electric field, we propose that the 0.59 eV signature in the highest Zr-doped sample likely corresponds to the 0.71 eV signature in lowerdoped samples. Our analysis highlights the importance of testing for and reporting on field

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Generation and metastability of deep level states in β-Ga2O3 exposed to reverse bias at elevated temperatures

Abstract: Impact of proton irradiation on conductivity and deep level defects in-Ga 2 O 3

Cited by 18 publications

References 27 publications

Ti- and Fe-related charge transition levels in β−Ga2O3

Ti- and Fe-related charge transition levels in β−Ga2O3

Formation and control of the E2∗ center in implanted β-Ga 2 O 3 by reverse-bias and zero-bias annealing

Defect states and their electric field-enhanced electron thermal emission in heavily Zr-doped β -Ga2O3 crystals

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