Article
Physics, Applied
Wanlin Zhu, John Hayden, Fan He, Jung-In Yang, Pannawit Tipsawat, Mohammad D. Hossain, Jon-Paul Maria, Susan Trolier-McKinstry
Summary: This study reveals the temperature dependence of ferroelectric switching in Al0.84Sc0.16N, Al0.93B0.07N, and AlN thin films, showing strong temperature dependence on polarization reversal and coercive field, while minimal temperature dependence on remanent polarization values. The relative permittivity increased within a certain temperature range, and polarization reversal was confirmed through piezoelectric coefficient analysis and chemical etching. Models based on thermal activation suggest a distribution of pinning sites or nucleation barriers regulates the switching behavior with an average activation energy near 28 meV.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Multidisciplinary
Hang Zang, Zhiming Shi, Mingrui Liu, Yuping Jia, Ke Jiang, Jianwei Ben, Yang Chen, Shunpeng Lv, Xiaojuan Sun, Dabing Li
Summary: In this study, the atomic structure of Al1-xScxN and its effect on its piezoelectric and ferroelectric properties were investigated using first-principles calculations. It was found that Al1-xScxN with a phase separation feature was more stable than the corresponding wurtzite structure. The piezoelectric response of Al1-xScxN depended strongly on the atomic arrangements, with different structures exhibiting positive and negative piezoelectric coefficients.
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(2023)
Article
Materials Science, Multidisciplinary
C. Yuan, M. Park, Y. Zheng, J. Shi, R. Dargis, S. Graham, A. Ansari
Summary: This study investigates phonon scattering processes and thermal conductivity in Al1-xScxN alloys grown by molecular beam epitaxy. The results show a decreasing trend in thermal conductivity with increasing scandium content, with an increase in thermal conductivity with temperature below 200 K and a plateau at higher temperatures. Application of an analytical model helps estimate the effects of scattering mechanisms on thermal conductivity behavior.
MATERIALS TODAY PHYSICS
(2021)
Article
Chemistry, Physical
Wenzheng Jiang, Lei Zhu, Lingli Chen, Yumeng Yang, Xi Yu, Xiaolong Li, Zhiqiang Mu, Wenjie Yu
Summary: In this study, an in situ method based on synchrotron X-ray diffraction (XRD) system was proposed to characterize the longitudinal piezoelectric constant d(33) of Al1-xScxN film. The measurement results showed the piezoelectric effect of Al1-xScxN films by lattice spacing variation upon applied external voltage. The in situ synchrotron XRD measurement was proven to be an effective method for precise piezoelectric coefficient d(33) characterization.
Article
Physics, Applied
Keisuke Yazawa, Andriy Zakutayev, Geoff L. Brennecka
Summary: This study presents a thermodynamic analysis of nitride ferroelectric materials using the classic Landau-Devonshire approach. The results show that the energy barrier's strain sensitivity in wurtzite ferroelectrics is higher compared to classic perovskite ferroelectrics.
APPLIED PHYSICS LETTERS
(2022)
Article
Chemistry, Physical
Yishui Ding, Xiangyu Hou, Tengyu Jin, Yanan Wang, Xu Lian, Yuan Liu, Yihe Wang, Sisheng Duan, Xiangrui Geng, Meng Wang, Jingyu Mao, Yuanyuan Zhang, Peirong Tang, Minghua Li, Huamao Lin, Yao Zhu, Siewlang Teo, Qiang Zhu, Ming Lin, Wei Chen
Summary: In this study, the growth mechanism and interfacial chemistry of ultrathin platinum and molybdenum films on high-crystalline Al1-xScxN surface were investigated. The chemical and electronic structure evolution of the interface during the deposition process were examined using in-situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The structural properties of the interface were characterized by cross-sectional transmission electron microscopy, X-ray diffraction spectroscopy, and atomic force microscopy. The study reveals the formation of ionic Pt2+-N bonds at the Pt/Al1-xScxN interface, while molybdenum does not bond with the substrate. Furthermore, electron transfer induces upward band-bending effects on the Al1-xScxN surface upon both platinum and molybdenum interactions. The research on the chemical and structural properties of ultrathin metal electrodes and Al1-xScxN interfaces provides guidance for designing high-performance micro-electromechanical devices.
APPLIED SURFACE SCIENCE
(2023)
Article
Materials Science, Multidisciplinary
Jiahui Yan, Yongxin Zhou, Songsong Zhang
Summary: This paper investigates the basic properties of ICP-RIE of scandium doped aluminum nitride thin films on silicon wafers, and proposes a pretreatment scheme to improve etching uniformity and wafer yield in the mass fabrication of Al1-xScxN-MEMS devices. The etching rate of 128 nm/min, low nonuniformity, and selectivity of 1.8 are achieved using a BCl3/Ar pretreatment and Cl2/Ar main etching scheme. The relationship between etching parameters and etching uniformity is revealed using a 5-step etching model.
Article
Physics, Applied
Md Redwanul Islam, Niklas Wolff, Mohamed Yassine, Georg Schoenweger, Bjorn Christian, Hermann Kohlstedt, Oliver Ambacher, Fabian Lofink, Lorenz Kienle, Simon Fichtner
Summary: This study found that the ferroelectric-to-paraelectric transition temperature of Al1-xScxN thin film can exceed 1100 degrees C, surpassing the transition temperature of virtually any other thin film ferroelectric. Through high-temperature X-ray diffraction and permittivity measurements, it was discovered that the wurtzite-type structure of Al0.73Sc0.27N remains stable during the entire 1100 degrees C annealing cycle.
APPLIED PHYSICS LETTERS
(2021)
Article
Nanoscience & Nanotechnology
Valerie Yoshioka, Jian Lu, Zichen Tang, Jicheng Jin, Roy H. Olsson, Bo Zhen
Summary: Silicon photonics has enabled large-scale production of integrated optical devices for various applications, but faces challenges when used in nonlinear devices. Scandium-doped aluminum nitride thin films exhibit enhanced optical second-order susceptibility, offering potential advantages for developing CMOS-compatible devices with strong nonlinearity.
Article
Chemistry, Multidisciplinary
Georg Schoenweger, Adrian Petraru, Md Redwanul Islam, Niklas Wolff, Benedikt Haas, Adnan Hammud, Christoph Koch, Lorenz Kienle, Hermann Kohlstedt, Simon Fichtner
Summary: This paper presents the first in-depth structural and electrical characterization of all-epitaxial, all-wurtzite-type ferroelectric III-N semiconductor heterostructures. The results show that Al1-xScxN films have multiple strain states and exhibit splitting of the ferroelectric displacement current into separate peaks. It is also observed that films grown on the metal-polar GaN template feature an initial multidomain state.
ADVANCED FUNCTIONAL MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Georg Schoenweger, Md Redwanul Islam, Niklas Wolff, Adrian Petraru, Lorenz Kienle, Hermann Kohlstedt, Simon Fichtner
Summary: This letter reports on room temperature switchable ultra-thin (10 nm) ferroelectric Al0.72Sc0.28N films, which are important for potential applications in neuromorphic computing and memory devices. All-epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering, and the Al0.72Sc0.28N film surface is protected by in situ Pt capping to avoid oxidation. The films exhibit good epitaxy and show only moderate scaling effects in terms of relative permittivity and coercive field dependence, suggesting that the critical thickness for ferroelectricity has not yet been reached.
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS
(2023)
Article
Physics, Applied
N. M. Feil, E. Mayer, A. Nair, B. Christian, A. Ding, C. Sun, S. Mihalic, M. Kessel, A. Zukauskaite, O. Ambacher
Summary: The study investigated the SAW modes in epitaxial Al0.68Sc0.32N(0001) films on Al2O3(0001) substrates, highlighting enhanced wave guidance and electromechanical coupling for the Sezawa mode in the <1<1>00> propagation direction. Additionally, simulations using finite element method and Green function approach identified different wave types, including Rayleigh, Sezawa, and shear-horizontal wave modes. Selecting high mass density electrodes and specific Sc concentration x in combination with SAW propagation direction could result in increased electromechanical coupling and phase velocities for the Sezawa mode.
JOURNAL OF APPLIED PHYSICS
(2021)
Article
Chemistry, Analytical
Zichen Tang, Giovanni Esteves, Jeffrey Zheng, Roy H. Olsson
Summary: Due to their favorable electromechanical properties, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al1-xScxN) thin films have been widely used in radio frequency (RF) acoustic devices. However, the resistance to etching at high scandium alloying has hindered the realization of devices that can fully utilize the highest electromechanical coupling coefficients. In this study, the etch rates of AlN and Al1-xScxN with different scandium concentrations were investigated. The findings provide valuable insights for structure/composition analysis and potential applications.
Article
Chemistry, Analytical
Niklas Wolff, Md Redwanul Islam, Lutz Kirste, Simon Fichtner, Fabian Lofink, Agne Zukauskaite, Lorenz Kienle
Summary: Research on wurtzite-type aluminum scandium nitride (Al1-xScxN) thin films revealed an anomalous thermal expansion at high temperatures, attributed to the coupling contributions of intrinsic and extrinsic factors. This finding is significant for the manufacturing and operation of Al1-xScxN-based devices.
Article
Physics, Applied
Junji Kataoka, Sung-Lin Tsai, Takuya Hoshii, Hitoshi Wakabayashi, Kazuo Tsutsui, Kuniyuki Kakushima
Summary: Research on 50 nm thick ferroelectric Al0.78Sc0.22N films with TiN electrodes revealed that the leakage current gradually shifted during initial switching, stabilizing at a specific value. This change was interpreted as the formation of a tunneling barrier due to nitrogen vacancies at the metal interface.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2021)
Article
Physics, Applied
Joseph Casamento, Hyunjea Lee, Takuya Maeda, Ved Gund, Kazuki Nomoto, Len van Deurzen, Wesley Turner, Patrick Fay, Sai Mu, Chris G. van de Walle, Amit Lal, Huili (Grace) Xing, Debdeep Jena
Summary: Epitaxial ScxAl1-xN thin films grown on metal polar GaN substrates exhibit high relative dielectric permittivity, the largest among existing nitride materials. The films also have polarization discontinuity, which can be utilized for extending transistor operation in power electronics and high-speed microwave applications.
APPLIED PHYSICS LETTERS
(2022)
Article
Physics, Applied
Xie Zhang, Mark E. Turiansky, Jimmy-Xuan Shen, Chris G. van de Walle
Summary: This Perspective critically discusses the defect tolerance in halide perovskites based on first-principles calculations. It shows that halide perovskites are not defect tolerant and suffer from defect-assisted nonradiative recombination, with comparable or higher nonradiative recombination rates than conventional semiconductors. The importance of accurate defect properties and defect engineering in improving the efficiency of perovskite solar cells is highlighted.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Joshua Leveillee, Samuel Ponce, Nicholas L. Adamski, Chris G. Van de Walle, Feliciano Giustino
Summary: The possibility of improving the hole mobility of GaN by epitaxial matching to ZnGeN2 and MgSiN2 is explored. Calculations show that lattice matching with these materials can lead to the inversion of certain hole bands and significantly increase hole mobility.
APPLIED PHYSICS LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Sai Mu, Chris G. Van de Walle
Summary: This study uses density functional theory to assess the phase stability of monoclinic Ga2O3 and (AlxGa1-x)(2)O-3 alloys. It finds that the gamma and kappa phases of (AlxGa1-x)(2)O-3 have the lowest enthalpy of formation at 62.5% and 50% Al concentrations, respectively. At finite temperature, lattice vibrations tend to stabilize the kappa phase and destabilize the alpha and gamma phases, with the configurational entropy of the gamma phase playing a substantial role in stabilizing it.
PHYSICAL REVIEW MATERIALS
(2022)
Article
Physics, Applied
Su-Hyun Yoo, Mira Todorova, Jorg Neugebauer, Chris G. Van de Walle
Summary: GaN/(Al, Ga)N heterojunctions are crucial for high-electron-mobility transistors. The density of the two-dimensional electron gas (2DEG) on the GaN side is significantly enhanced by the strong polarization fields at the interface. The source of the electrons in the 2DEG is intrinsic to the overall structure and the negative charge is balanced by fixed charge on the surface, rather than surface states.
PHYSICAL REVIEW APPLIED
(2023)
Article
Quantum Science & Technology
Mehmet T. Uysal, Mouktik Raha, Songtao Chen, Christopher M. Phenicie, Salim Ourari, Mengen Wang, Chris G. Van de Walle, Viatcheslav V. Dobrovitski, Jeff D. Thompson
Summary: In this work, coherent coupling between the electron spin of a single Er3+ ion and a single I = 1/2 nuclear spin in the solid-state host crystal, which is a fortuitously located proton (1H), is demonstrated. The nuclear spin is controlled using dynamical-decoupling sequences applied to the electron spin, allowing for one- and two-qubit gate operations. The longer coherence time of the nuclear spin, compared to the electron spin, is crucial for combining long-lived nuclear spin quantum registers with telecom-wavelength emitters for long-distance quantum repeaters.
Article
Physics, Multidisciplinary
Fangzhou Zhao, Mark E. Turiansky, Audrius Alkauskas, Chris G. Van de Walle
Summary: Trap-assisted Auger-Meitner recombination is highlighted as a dominant nonradiative process in wide-band-gap materials, and a first-principles methodology is presented to determine the rates of this process in semiconductors or insulators due to defects or impurities.
PHYSICAL REVIEW LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Ymir K. Frodason, Joel B. Varley, Klaus Magnus H. Johansen, Lasse Vines, Chris G. Van de Walle
Summary: Pathways and energy barriers for the migration of Ga vacancies (VGa) and Ga interstitials (Gai) in-Ga2O3 have been studied using hybrid functional calculations and the nudged elastic band method. A mechanism for the transformation of VGa between different split configurations has been described. The overall migration barriers for VGa and Gai in different crystal directions have been determined. The results provide insights into the thermally activated recovery processes in irradiated material.
Article
Quantum Science & Technology
Raj N. Patel, David A. Hopper, Jordan A. Gusdorff, Mark E. Turiansky, Tzu-Yung Huang, Rebecca E. K. Fishman, Benjamin Porat, Chris G. Van de Walle, Lee C. Bassett
Summary: By using photon emission correlation spectroscopy, we revealed the optical dynamics of quantum emitters in hexagonal boron nitride. The experimental results showed the existence of quantum emitters with ideal single-photon emission and their photoluminescence emission lineshapes were consistent with individual vibronic transitions. However, polarization-resolved excitation and emission revealed the role of multiple optical transitions, and photon emission correlation spectroscopy revealed the complicated optical dynamics associated with excitation and relaxation.
Proceedings Paper
Engineering, Electrical & Electronic
Mengen Wang, Sai Mu, Chris G. Van de Walle
Summary: This paper discusses the diffusion behavior of dopants and point defects in monoclinic gallium oxide, as well as the diffusion of hydrogen in gallium oxide. The results provide important guidance for controlling doping in gallium oxide and its alloys.
OXIDE-BASED MATERIALS AND DEVICES XIII
(2022)
Article
Materials Science, Multidisciplinary
Sai Mu, Mengen Wang, Joel B. Varley, John L. Lyons, Darshana Wickramaratne, Chris G. Van de Walle
Summary: We used hybrid density functional calculations to analyze n-type doping in monoclinic (AlxGa1-x)(2)O-3 alloys. Our study focused on the impact of silicon, carbon, and hydrogen as impurities in metal-organic chemical vapor deposition (MOCVD) and their effect on the structural properties and charge-state transition levels of the alloys.
Article
Physics, Multidisciplinary
Sai Mu, Kiranmayi D. Dixit, Xiaoping Wang, Douglas L. Abernathy, Huibo Cao, Stephen E. Nagler, Jiaqiang Yan, Paula Lampen-Kelley, David Mandrus, Carlos A. Polanco, Liangbo Liang, Gabor B. Halasz, Yongqiang Cheng, Arnab Banerjee, Tom Berlijn
Summary: This study investigates the phonon structure of alpha-RuCl3 and finds that certain phonons in the material have significantly reduced velocities, potentially dominating the observability of the half-integer plateaus in the thermal Hall conductance. The findings are crucial for understanding the controversy surrounding the observation of this phenomenon.
PHYSICAL REVIEW RESEARCH
(2022)
