β-Ga2O3 is gaining increasing attention from power device engineers owing to its wide bandgap and fabrication potential of low-cost, large-diameter substrates. Atomic-layer-deposited (ALD) Al2O3 has application potential for the gate insulation and surface passivation of β-Ga2O3 devices, which cannot incorporate a well-established SiO2/Si system. To improve the device performance and reliability, the effect of postdeposition annealing (PDA) on the gate insulation characteristics of Al/ALD-Al2O3/(001) β-Ga2O3 capacitors was comprehensively investigated. As in previous studies, PDA at 700 °C and higher sharply reduced the capacitor leakage current by three orders of magnitude. This threshold temperature was 100 °C lower than that for GaN devices. Space-charge-controlled field emission analysis revealed that the current reduction was achieved via conduction-band-offset enhancement from 1.45 to 2.2 eV. These changes were caused by Al2O3 crystallization, which started at 650 °C according to an x-ray diffraction analysis. Selective-area electron diffraction (SAED) patterns showed that the crystallized films comprised twinned γ-Al2O3, wherein the (111) planes are parallel to the sawtooth β-Ga2O3 (101) planes with epitaxial relations of γ-Al2O3 || β-Ga2O3 [010] and γ-Al2O3 || β-Ga2O3 [010]. This epitaxy was realized by three-dimensional oxygen sublattice matching with relatively small misfits of less than 1%, 1%, and 8% along the γ-Al2O3 , [111], and directions, respectively. Furthermore, the SAED patterns displayed diffraction spots specific to triaxially tripled γ-Al2O3. This is yet to be identified as δ-Al2O3. Contrary to expectations, PDA magnified the bias instability of β-Ga2O3 capacitors, supposedly owing to the Al2O3 and Ga2O3 solid-solution reaction, which contrasts with the previous significant improvement in GaN capacitors. However, PDA negligibly affected the β-Ga2O3 capacitor interface characteristics. This result also contrasts sharply with the previous results obtained for GaN capacitors that experienced a PDA-induced increase in both interface states and flat-band voltage. This apparent thermal stability of Al2O3/(001) β-Ga2O3 interface can be ascribed to the aforementioned small lattice misfit at the γ-Al2O3/(101) β-Ga2O3 interface, which contrasts with the 12% misfit at the γ-Al2O3/(0001) GaN interface. These findings form the foundation for developing technologies to enhance the performance and reliability of ALD-Al2O3/β-Ga2O3 devices. Specifically, based on them, a guideline for reducing the bias instability is proposed.
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Postdeposition annealing effect on atomic-layer-deposited Al2O3 gate insulator on (001) β-Ga2O3
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December 2021
Research Article|
October 15 2021
Postdeposition annealing effect on atomic-layer-deposited Al2O3 gate insulator on (001) β-Ga2O3
Atsushi Hiraiwa (平岩篤)
;
Atsushi Hiraiwa (平岩篤)
a)
1
Research Organization for Nano and Life Innovation, Waseda University
, 513 Waseda-tsurumaki, Shinjuku, Tokyo 162-0041, Japan
2
The Kagami Memorial Laboratory for Materials Science and Technology, Waseda University
, 2-8-26 Nishiwaseda, Shinjuku, Tokyo 169-0051, Japan
a)Author to whom correspondence should be addressed: [email protected]
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Kiyotaka Horikawa (堀川清貴)
;
Kiyotaka Horikawa (堀川清貴)
3
Faculty of Science and Engineering, Waseda University
, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
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Hiroshi Kawarada (川原田洋)
;
Hiroshi Kawarada (川原田洋)
1
Research Organization for Nano and Life Innovation, Waseda University
, 513 Waseda-tsurumaki, Shinjuku, Tokyo 162-0041, Japan
2
The Kagami Memorial Laboratory for Materials Science and Technology, Waseda University
, 2-8-26 Nishiwaseda, Shinjuku, Tokyo 169-0051, Japan
3
Faculty of Science and Engineering, Waseda University
, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
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Motohisa Kado (加渡幹尚);
Motohisa Kado (加渡幹尚)
4
Advanced Material Engineering Division, Toyota Motor Corporation
, 1200 Mishuku, Susono, Shizuoka 410-1193, Japan
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Katsunori Danno (旦野克典)
Katsunori Danno (旦野克典)
4
Advanced Material Engineering Division, Toyota Motor Corporation
, 1200 Mishuku, Susono, Shizuoka 410-1193, Japan
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a)Author to whom correspondence should be addressed: [email protected]
J. Vac. Sci. Technol. B 39, 062205 (2021)
Article history
Received:
August 15 2021
Accepted:
September 29 2021
Citation
Atsushi Hiraiwa, Kiyotaka Horikawa, Hiroshi Kawarada, Motohisa Kado, Katsunori Danno; Postdeposition annealing effect on atomic-layer-deposited Al2O3 gate insulator on (001) β-Ga2O3. J. Vac. Sci. Technol. B 1 December 2021; 39 (6): 062205. https://doi.org/10.1116/6.0001360
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