Gallium oxide (Ga2O3), a promising candidate for high-power electronics, may be doped with Fe to control the native n-type conductivity and produce semi-insulating single-crystalline substrates. Here, intentionally as well as unintentionally Fe-doped β-Ga2O3 crystals grown by the Czochralski (Cz) and the floating zone (FZ) methods are studied. While the Cz samples contain Ir on the order of 1017 cm−3 due to the Ir crucible, the FZ samples are free of this contaminant. Photoinduced electron paramagnetic resonance (EPR) is performed by illuminating the samples with light emitting diodes from 0.7 to 4.7 eV while monitoring the intensity of the EPR signal. The following optical transitions associated with Fe are observed: one between 1 and 2 eV occurs in both Cz and FZ samples, another near 2.5 eV is unique to Cz Ga2O3, and a third near 3 eV appears in FZ material. The transition below 2 eV is the well-studied Fe2+-to-Fe3+ transition, intrinsic to Fe. Near 2.5 and 3 eV, the amount of Fe3+ decreases by capturing electrons excited from other defects present near or below the middle of the bandgap. By comparing Cz and Ir-free FZ crystals, we show that the 2.5 eV transition is primarily caused by Ir in Fe-doped Cz samples, whereas the ∼3 eV transition observed in FZ samples could be caused by isolated or complex intrinsic defects. By differentiating transitions between Cz and FZ material, the results will be relevant to epitaxial films, which do not contain the Ir present in the commonly studied Cz material.
REFERENCES
1.
S. J.
Pearton
, J.
Yang
, P. H.
Cary
, F.
Ren
, J.
Kim
, M. J.
Tadjer
, and M. A.
Mastro
, “A review of Ga2O3 materials, processing, and devices
,” Appl. Phys. Rev.
5
, 011301
(2018
). 2.
M.
Higashiwaki
, K.
Sasaki
, A.
Kuramata
, T.
Masui
, and S.
Yamakoshi
, “Gallium oxide (Ga2O3) metal-semiconductor field-effect transistors on single-crystal β-Ga2O3 (010) substrates
,” Appl. Phys. Lett.
100
, 013504
(2012
). 3.
J.
Zhang
, J.
Shi
, D.-C.
Qi
, L.
Chen
, and K. H. L.
Zhang
, “Recent progress on the electronic structure, defect, and doping properties of Ga2O3
,” APL Mater.
8
, 020906
(2020
). 4.
C.
Xie
, X.-T.
Lu
, X.-W.
Tong
, Z.-X.
Zhang
, F.-X.
Liang
, L.
Liang
, L.-B.
Luo
, and Y.-C.
Wu
, “Recent progress in solar-blind deep-ultraviolet photodetectors based on inorganic ultrawide bandgap semiconductors
,” Adv. Funct. Mater.
29
, 1806006
(2019
). 5.
E. G.
Villora
, K.
Shimamura
, Y.
Yoshikawa
, K.
Aoki
, and N.
Ichinose
, “Large-size β-Ga2O3 single crystals and wafers
,” J. Cryst. Growth
270
, 420
–426
(2004
). 6.
Z.
Galazka
, K.
Irmscher
, R.
Uecker
, R.
Bertram
, M.
Pietsch
, A.
Kwasniewski
, M.
Naumann
, T.
Schulz
, R.
Schewski
, and D.
Klimm
, “On the bulk β-Ga2O3 single crystals grown by the Czochralski method
,” J. Cryst. Growth
404
, 184
(2014
). 7.
A.
Kuramata
, K.
Koshi
, S.
Watanabe
, Y.
Yamaoka
, T.
Masui
, and S.
Yamakoshi
, “High-quality β-Ga2O3 single crystals grown by edge-defined film-fed growth
,” Jpn. J. Appl. Phys.
55
, 1202A2
(2016
). 8.
A. T.
Neal
, S.
Mou
, S.
Rafique
, H.
Zhao
, E.
Ahmadi
, J. S.
Speck
, K. T.
Stevens
, J. D.
Blevins
, D. B.
Thomson
, N.
Moser
, K. D.
Chabak
, and G. H.
Jessen
, “Donors and deep acceptors in β-Ga2O3
,” Appl. Phys. Lett.
113
, 062101
(2018
). 9.
J. R.
Ritter
, J.
Huso
, P. T.
Dickens
, J. B.
Varley
, K. G.
Lynn
, and M. D.
McCluskey
, “Compensation and hydrogen passivation of magnesium acceptors in β-Ga2O3
,” Appl. Phys. Lett.
113
, 052101
(2018
). 10.
J. F.
McGlone
, Z.
Xia
, C.
Joishi
, S.
Lodha
, S.
Rajan
, S.
Ringel
, and A. R.
Arehart
, “Identification of critical buffer traps in Si δ-doped β-Ga2O3 MESFETs
,” Appl. Phys. Lett.
115
, 153501
(2019
). 11.
A.
Mauze
, Y.
Zhang
, T.
Mates
, F.
Wu
, and J. S.
Speck
, “Investigation of unintentional Fe incorporation in (010) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy
,” Appl. Phys. Lett.
115
, 052102
(2019
). 12.
M. H.
Wong
, K.
Sasaki
, A.
Kuramata
, S.
Yamakoshi
, and M.
Higashiwaki
, “Anomalous Fe diffusion in Si-ion-implanted β-Ga2O3 and its suppression in Ga2O3 transistor structures through highly resistive buffer layers
,” Appl. Phys. Lett.
106
, 032105
(2015
). 13.
E. G.
Víllora
, K.
Shimamura
, Y.
Yoshikawa
, T.
Ujiie
, and K.
Aoki
, “Electrical conductivity and carrier concentration control in β-Ga2O3 by Si doping
,” Appl. Phys. Lett.
92
, 202120
(2008
). 14.
A. Y.
Polyakov
, N. B.
Smirnov
, I. V.
Shchemerov
, S. J.
Pearton
, F.
Ren
, A. V.
Chernykh
, and A. I.
Kochkova
, “Electrical properties of bulk semi-insulating β-Ga2O3 (Fe)
,” Appl. Phys. Lett.
113
, 142102
(2018
). 15.
Z.
Hu
, K.
Nomoto
, W.
Li
, N.
Tanen
, K.
Sasaki
, A.
Kuramata
, T.
Nakamura
, D.
Jena
, and H. G.
Xing
, “Enhancement-mode Ga2O3 vertical transistors with breakdown voltage >1kV
,” IEEE Electron Device Lett.
39
, 869
–872
(2018
). 16.
M.
Higashiwaki
, K.
Sasaki
, T.
Kamimura
, M.
Hoi Wong
, D.
Krishnamurthy
, A.
Kuramata
, T.
Masui
, and S.
Yamakoshi
, “Depletion-mode Ga2O3 metal-oxide semiconductor field-effect transistors on β-Ga2O3 (010) substrates and temperature dependence of their device characteristics
,” Appl. Phys. Lett.
103
, 123511
(2013
). 17.
J. B.
Varley
, A.
Janotti
, C.
Franchini
, and C. G.
Van de Walle
, “Role of self-trapping in luminescence and p-type conductivity of wide-band-gap oxide
,” Phy. Rev. B
85
, 081109(R)
(2012
). 18.
J. L.
Lyons
, “A survey of acceptor dopants for β-Ga2O3
,” Semicond. Sci. Technol.
33
, 05LT02
(2018
). 19.
M. H.
Wong
, C.-H.
Lin
, A.
Kuramata
, S.
Yamakoshi
, H.
Murakami
, Y.
Kumagai
, and M.
Higashiwaki
, “Acceptor doping of β-Ga2O3 by Mg and N ion implantations
,” Appl. Phys. Lett.
113
, 102103
(2018
). 20.
C. A.
Lenyk
, N. C.
Giles
, E. M.
Scherrer
, B. E.
Kananen
, L. E.
Halliburton
, K. T.
Stevens
, G. K.
Foundos
, J. D.
Blevins
, D. L.
Dorsey
, and S.
Mou
, “Ir4+ ions in β-Ga2O3 crystals: An unintentional deep donor
,” J. Appl. Phys.
125
, 045703
(2019
). 21.
S.
Bhandari
, M. E.
Zvanut
, and J. B.
Varley
, “Optical absorption of Fe in doped Ga2O3
,” J. Appl. Phys.
126
, 165703
(2019
). 22.
S.
Bhandari
and M. E.
Zvanut
, “Charge trapping at Fe due to midgap levels in Ga2O3
,” J. Appl. Phys.
129
, 085703
(2021
). 23.
J.
Weil
and J.
Bolton
, Electron Paramagnetic Resonance: Elementary Theory and Practical Applications
(John Wiley & Sons, Inc.
, 2007
), pp. 545
–546
.24.
S.
Bhandari
and M. E.
Zvanut
, “Optical transitions for impurities in Ga2O3 as determined by photo-induced electron paramagnetic resonance spectroscopy
,” J. Appl. Phys.
127
, 065704
(2020
). 25.
M. L.
Meil’man
, “EPR of Fe3+ ions in β-Ga2O3 crystals
,” Fizika Tverdogo Tela
11
(6), 1730
–1732 (1969
) [Fizika Tverdogo Tela
11(6), 1730–1732 (1969).26.
R.
Büscher
and G.
Lehmann
, “Correlation of zero-field splittings and site distortions. IX. Fe3+ and Cr3+ in β-Ga2O3
,” Z. Naturforsch.
42
, 67
(1987
). 27.
J. R.
Ritter
, K. G.
Lynn
, and M. D.
McCluskey
, “Iridium-related complexes in Czochralski-grown β-Ga2O3
,” J. Appl. Phys.
126
, 225705
(2019
). 28.
J. B.
Varley
, J. R.
Weber
, A.
Janotti
, and C. G.
Van de Walle
, “Oxygen vacancies and donor impurities in β-Ga2O3
,” Appl. Phys. Lett.
97
, 142106
(2010
). 29.
P.
Deak
, Q. D.
Ho
, F.
Seemann
, B.
Aradi
, M.
Lorke
, and T.
Frauenheim
, “Choosing the correct hybrid for defect calculations: A case study on intrinsic carrier trapping in β-Ga2O3
,” Phys. Rev. B
95
, 075208
(2017
). 30.
D.
Skachkov
, W. R. L.
Lambrecht
, H. J.
von Bardeleben
, U.
Gerstmann
, Q. D.
Ho
, and P.
Deák
, “Computational identification of Ga-vacancy related electron paramagnetic resonance centers in β-Ga2O3
,” J. Appl. Phys.
125
, 185701
(2019
). 31.
Y. K.
Frodason
, C.
Zimmermann
, E. F.
Verhoeven
, P. M.
Weiser
, L.
Vines
, and J. B.
Varley
, “Multistability of isolated and hydrogenated Ga–O divacancies in β-Ga2O3
,” Phys. Rev. Mater.
5
, 025402
(2021
). 32.
C. A.
Lenyk
, T. D.
Gustafson
, L. E.
Halliburton
, and N. C.
Giles
, “Deep donors and acceptors in β-Ga2O3 crystals: Determination of the Fe2+/3+ level by a noncontact method
,” J. Appl. Phys.
126
, 245701
(2019
). 33.
B. E.
Kananen
, L. E.
Halliburton
, K. T.
Stevens
, G. K.
Foundos
, and N. C.
Giles
, “Gallium vacancies in β-Ga2O3 crystals
,” Appl. Phys. Lett.
110
, 202104
(2017
). © 2021 Author(s). Published under an exclusive license by AIP Publishing.
2021
Author(s)
You do not currently have access to this content.
