Article
Chemistry, Physical
Zeyu Chi, Corinne Sartel, Yunlin Zheng, Sushrut Modak, Leonid Chernyak, Christian M. Schaefer, Jessica Padilla, Jose Santiso, Arie Ruzin, Anne-Marie Goncalves, Jurgen von Bardeleben, Gerard Guillot, Yves Dumont, Amador Perez-Tomas, Ekaterine Chikoidze
Summary: The room temperature hole conductivity of β-Ga2O3 was achieved by growing high-quality films on a sapphire substrate. The conductivity was significantly enhanced by zinc doping with low activation energy.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Physical
Yu Hizhnyi, V Borysyuk, V Chornii, S. Nedilko, P. O. Tesel'ko, O. Dubovik, P. Maksymchuk, I Tupitsyna, A. Yakubovskaya, M. Androulidaki, N. Klyui
Summary: Li2MoO4 crystals are considered as promising cryogenic scintillation materials for use in elementary particle physics experiments. This study presents experimental and computational investigations into the electronic structure and optical properties of the crystals, analyzing the spectral characteristics and the impact of defects on their scintillation properties.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Physical
Ruizhi Qiu, Jun Tang, Jinfan Chen, Bingyun Ao
Summary: The effect of atomic hydrogen adsorption on AnO(2) surfaces varies depending on the type of material, with surface metallicity induced in ThO2 but strongly suppressed in UO2 and PuO2 due to electronic correlation.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2021)
Article
Nanoscience & Nanotechnology
Ymir K. Frodason, Patryk P. Krzyzaniak, Lasse Vines, Joel B. Varley, Chris G. Van de Walle, Klaus Magnus H. Johansen
Summary: The diffusion of the n-type dopant Sn in beta-Ga2O3 was studied using secondary-ion mass spectrometry combined with hybrid functional calculations. It was found that Ga vacancies mediate the migration of Sn through the formation and dissociation of intermittent mobile VGaSnGa complexes. The migration barrier for the VGaSnGa complex was determined to be 3.0 +/- 0.4 eV, consistent with theoretical predictions using the nudged elastic band method.
Article
Chemistry, Physical
Abay B. Usseinov, Zhakyp T. Karipbayev, Juris Purans, Askhat B. Kakimov, Aizat Bakytkyzy, Amangeldy M. Zhunusbekov, Temirgali A. Koketai, Artem L. Kozlovskyi, Yana Suchikova, Anatoli I. Popov
Summary: This study successfully synthesized beta-Ga2O3 ceramic using high-energy electron beams, resulting in a monolithic structure with a close-to-ideal composition. X-ray diffraction analysis confirmed the monoclinic structure, while photoluminescence spectra revealed multiple luminescence peaks. Raman spectroscopy further confirmed the bonding modes in the synthesized ceramic. The electron beam-assisted method offers a rapid and cost-effective approach for beta-Ga2O3 ceramic production.
Article
Physics, Applied
Mark E. Turiansky, Darshana Wickramaratne, John L. Lyons, Chris G. Van de Walle
Summary: The study suggests that Si-B and O-N are potential dopants for cubic boron nitride, with low formation energies and no self-compensation. However, compensation by boron vacancies poses a challenge that needs to be addressed with specific strategies.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
Adrian Chmielewski, Ziling Deng, Muad Saleh, Jani Jesenovec, Wolfgang Windl, Kelvin Lynn, John McCloy, Nasim Alem
Summary: The study investigates the atomic and electronic structure of a Hf-doped beta-gallium oxide crystal and finds that Hf dopants prefer octahedral sites and have little impact on the crystal structure. The bandgap values of Hf-doped beta-Ga2O3 are similar to those of unintentionally doped crystals, making Hf an excellent dopant candidate.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Condensed Matter
Alina Kononov, Cheng-Wei Lee, Ethan P. Shapera, Andre Schleife
Summary: This study reevaluates native point defect geometries in alpha-Al2O3 and identifies new defect configurations that could have transformative impacts on our understanding of defect migration pathways in aluminum-oxide scales.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2023)
Article
Chemistry, Physical
Rina Ibragimova, Patrick Rinke, Hannu-Pekka Komsa
Summary: This study investigates the formation energies of metal, carbon, and nitrogen vacancies in MXene materials using first-principles calculations. The results show significant differences in the formation energies of metal vacancies under different surface functionalizations and environments. Carbon and nitrogen vacancies are found to be more prevalent in oxygen-functionalized surfaces. The study also highlights the influence of pH value and electrode potential on vacancy formation.
CHEMISTRY OF MATERIALS
(2022)
Article
Chemistry, Inorganic & Nuclear
Fatima Safieddine, Fouad El Haj Hassan, Michel Kazan
Summary: In this study, the FP-LAPW thorn lo method was used to investigate the properties of Ga2O3, including structural, electronic, elastic, optical, thermodynamic, and transport properties. The results show that Ga2O3 has potential applications in optoelectronics and thermoelectrics.
JOURNAL OF SOLID STATE CHEMISTRY
(2022)
Article
Chemistry, Physical
Neeraj Mishra, Guy Makov
Summary: The energetic and electronic properties of intrinsic point defects in germanium sulfide (GeS) were investigated using first-principles methods. It was found that the Schottky dimer (SD) is the most stable neutral defect, and Ge vacancies are the most stable defects in both Ge-rich and Ge-poor environments. GeS exhibits nonstoichiometric properties. The introduction of point defects affects the electronic structure of GeS, and Ge vacancies induce p-type conductivity.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Chemistry, Multidisciplinary
Laura E. Ratcliff, Takayoshi Oshima, Felix Nippert, Benjamin M. Janzen, Elias Kluth, Rudiger Goldhahn, Martin Feneberg, Piero Mazzolini, Oliver Bierwagen, Charlotte Wouters, Musbah Nofal, Martin Albrecht, Jack E. N. Swallow, Leanne A. H. Jones, Pardeep K. Thakur, Tien-Lin Lee, Curran Kalha, Christoph Schlueter, Tim D. Veal, Joel B. Varley, Markus R. Wagner, Anna Regoutz
Summary: Ga2O3 and its polymorphs have great potential for electronic structure engineering. In this study, a robust atomistic model of gamma-Ga2O3 is developed using density functional theory and machine-learning approach, which is validated by experimental results. This work is of significant importance for understanding the electronic structure of complex, disordered oxides.
ADVANCED MATERIALS
(2022)
Article
Physics, Applied
Micah S. S. Haseman, Daram N. N. Ramdin, Wenshen Li, Kazuki Nomoto, Debdeep Jena, Huili Grace Xing, Leonard J. J. Brillson
Summary: This study investigates the movement of electrically charged defects in Ga2O3 vertical trench power diodes using cathodoluminescence point spectra and hyperspectral imaging. The researchers observed the spatial rearrangement of optically active defects under strong reverse bias. These findings demonstrate the potential impact of extreme electric fields on atomic rearrangement and local doping changes in beta-Ga2O3, highlighting the importance of nanoscale device geometry in other high-power semiconductor devices.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Physical
Gurudayal Behera, Vikram, Akash Kumar, Kavaipatti Balasubramaniam, Aftab Alam
Summary: MoOx has emerged as a promising candidate for passivating, hole-selective layers in silicon photovoltaic devices, with Bader charge analysis indicating strong interactions between Si and MoO3. The distortion in the Si lattice is significantly higher for alpha-MoO3/Si compared to beta-MoO3/Si, leading to better surface passivation. Surface passivation is further improved by non-stoichiometric, oxygen vacancy-doped beta-MoOx, with the best results observed for 5% oxygen vacancy in beta-MoO3.
JOURNAL OF PHYSICAL CHEMISTRY C
(2021)
Article
Materials Science, Multidisciplinary
M. Garnica, M. M. Otrokov, P. Casado Aguilar, I. I. Klimovskikh, D. Estyunin, Z. S. Aliev, I. R. Amiraslanov, N. A. Abdullayev, V. N. Zverev, M. B. Babanly, N. T. Mamedov, A. M. Shikin, A. Arnau, A. L. Vazquez de Parga, E. Chulkov, R. Miranda
Summary: We investigated the surface crystalline and electronic structures of the antiferromagnetic topological insulator MnBi2Te4 using STM/S, ARPES, and density functional theory calculations. Our findings reveal the presence of native point defects at the crystal surface and nonuniform defect concentrations within crystals and among different samples. Additionally, the experiments indicate that the Dirac point gap of the topological surface state varies among different samples and sample cleavages. Our calculations demonstrate that the antiparallel alignment of Mn-Bi moments can lead to a reduction in the Dirac point gap size. This study provides important insights into the debated issue of the MnBi2Te4 Dirac point gap.
NPJ QUANTUM MATERIALS
(2022)
Article
Nanoscience & Nanotechnology
Takeshi Aihara, Wataru Aoki, Shin Kiyohara, Yu Kumagai, Keigo Kamata, Michikazu Hara
Summary: In this study, perovskite oxide nanoparticles were successfully synthesized using dicarboxylic acids as reagents. The resulting SrTiO3 nanoparticles showed high catalytic activity for the cyanosilylation of carbonyl compounds, even without a heat pretreatment.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Physics, Applied
Bunichiro Mikake, Takuma Kobayashi, Hidetoshi Mizobata, Mikito Nozaki, Takayoshi Shimura, Heiji Watanabe
Summary: The effect of post-deposition annealing on the electrical characteristics of SiO2/GaN MOS devices was investigated. Oxygen annealing was used to form an interfacial GaO x layer and forming gas annealing was used to passivate the remaining defects. Care must be taken not to produce a fixed charge through reduction of the GaO x layer. By growing the GaO x layer with oxygen annealing at 800 degrees C and performing forming gas annealing at a low temperature of 200 degrees C, it became possible to suppress the reduction of GaO x and to reduce the interface traps, oxide traps, and fixed charge simultaneously.
APPLIED PHYSICS EXPRESS
(2023)
Article
Chemistry, Physical
Yasuhide Mochizuki, Ha-Jun Sung, Tomoya Gake, Fumiyasu Oba
Summary: An evolutionary algorithm combined with first-principles calculations is used to predict the reconstructed surface structures of nonmetallic perovskite oxides. The study identifies four lowest-energy reconstruction patterns for the (001) surfaces of various perovskite oxides. The results provide general insights into the surface reconstruction and band alignment of these oxides.
CHEMISTRY OF MATERIALS
(2023)
Article
Physics, Applied
Takayoshi Shimura, Ryoga Yamaguchi, Naoto Tabuchi, Masato Kondoh, Mizuki Kuniyoshi, Takuji Hosoi, Takuma Kobayashi, Heiji Watanabe
Summary: We investigated the influence of laser scan speed and power on the Sn fraction and crystallinity of GeSn wires. The Sn fraction increased from 1% to 3.5% with increasing scan speed, resulting in a luminescence wavelength shift. Higher laser power reduced the Sn fraction and caused a blue shift in the luminescence wavelength. We discussed these phenomena based on the growth kinetics of zone melting.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physics, Applied
Kentaro Onishi, Takuma Kobayashi, Hidetoshi Mizobata, Mikito Nozaki, Akitaka Yoshigoe, Takayoshi Shimura, Heiji Watanabe
Summary: By sputter deposition of SiO2, we minimized the formation of unstable GaO x layer, as confirmed by negligible GaO x growth even after post-deposition oxygen annealing up to 600 degrees C. A MOS device with negligible capacitance-voltage hysteresis, stable flat-band voltage, and low leakage current was demonstrated by performing oxygen and forming gas annealing at temperatures of 600 degrees C and 400 degrees C, respectively.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physics, Applied
Yu Kumagai
Summary: Although n-type transparent conducting oxides (TCOs) have been widely used in industry, p-type TCOs have not been commercialized. In this study, computational screening was used to search for promising p-type TCOs. Optical absorption spectra and formation energies of oxygen vacancies were used as screening parameters. As a result, six potential p-type TCOs were identified. Among them, Na3AgO2, Rb2Pb2O3, and Cs2Pb2O3 were newly discovered, while CsCuO, K2Pb2O3, and B6O were previously proposed. Detailed analysis showed that Na3AgO2, CsCuO, and K2Pb2O3 exhibit p-type conductivity without external doping, validating the use of oxygen vacancy formation energies as descriptors for p-type dopability of oxides.
PHYSICAL REVIEW APPLIED
(2023)
Article
Chemistry, Multidisciplinary
Takafumi Yamamoto, Shogo Kawaguchi, Taiki Kosuge, Akira Sugai, Naoki Tsunoda, Yu Kumagai, Kosuke Beppu, Takuya Ohmi, Teppei Nagase, Kotaro Higashi, Kazuo Kato, Kiyofumi Nitta, Tomoya Uruga, Seiji Yamazoe, Fumiyasu Oba, Tsunehiro Tanaka, Masaki Azuma, Saburo Hosokawa
Summary: The reaction pathway of the solid-gas reduction of layered perovskite Sr3Fe2O7-delta was revealed using high-speed time-resolved synchrotron X-ray techniques. The pristine Sr3Fe2O7-delta showed a gradual single-phase structural evolution during reduction, while a nonequilibrium dynamically-disordered phase emerged in the reduction of a Pd-loaded sample before a first-order transition. This change in reaction pathway can be explained by a change in the rate-determining step. The synchrotron X-ray technique has the potential to be applied to other solid-gas reactions for a better understanding and optimization of reactions in solid-state compounds.
Article
Physics, Applied
Hidetoshi Mizobata, Mikito Nozaki, Takuma Kobayashi, Takayoshi Shimura, Heiji Watanabe
Summary: The density and energy level of hole traps in GaN-based metal-oxide-semiconductor (MOS) devices depend crucially on the concentration of magnesium (Mg) dopants in the GaN layers. Regardless of the degree of dopant activation, MOS capacitors on heavily Mg-doped GaN epilayers demonstrate hole accumulation and very low interface state densities.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Hiroki Fujimoto, Takuma Kobayashi, Takayoshi Shimura, Heiji Watanabe
Summary: This paper presents a method to selectively introduce nitrogen at the SiC-side of the SiO2/SiC interface, resulting in significantly low D(it) values near the conduction band edge of SiC. The interface properties were hardly degraded by excimer ultraviolet light irradiation, indicating better stability compared with a NO-nitrided sample.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Nobuyuki Tanaka, Mizuki Kuniyoshi, Kazuya Abe, Masaki Hoshihara, Takuma Kobayashi, Takayoshi Shimura, Heiji Watanabe
Summary: Epitaxial growth of high-quality low tin content germanium (GeSn) alloy is achieved by sputter deposition with the addition of Sn. The crystallographic structure of the GeSn alloy is significantly improved, leading to intense photoluminescence even at room temperature. Dislocation-free single-crystal GeSn films are formed on a Ge(100) substrate under specific growth conditions, with a compositional gradation of the Sn content in the film thickness direction.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Takato Nakanuma, Kosuke Tahara, Katsuhiro Kutsuki, Takayoshi Shimura, Heiji Watanabe, Takuma Kobayashi
Summary: This study demonstrates control over color centers at the SiO2/SiC interface by designing oxidation and annealing conditions. The post-oxidation CO2 annealing technique reduces the number of color centers and forms well-isolated single photon emitters with bright emission. The correlation between color centers and electrically active defects is also discussed.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Shingo Ogawa, Hidetoshi Mizobata, Takuma Kobayashi, Takayoshi Shimura, Heiji Watanabe
Summary: The relationship between the electrical properties and carrier trap properties of SiO2/GaN MOS capacitors was studied using electrical measurements and DLTS. It was found that after annealing in O-2 ambient, the frequency dispersion of the C-V curves decreased and the density of interface trap states and oxide trap states significantly decreased, leading to the improvement of electrical properties.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physics, Applied
Takuma Kobayashi, Takayoshi Shimura, Heiji Watanabe
Summary: In this study, the feasibility of oxygen-vacancy complexes as spin defects in silicon carbide (SiC) was investigated using ab initio calculations. The OCVSi0 defect was found to possess desirable spin and optical properties, making it potentially attractive as a quantum bit.
JOURNAL OF APPLIED PHYSICS
(2023)
