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
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, 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
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
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
Physics, Applied
John Hayden, Joseph Shepard, Jon-Paul Maria
Summary: Ferroelectric Al0.93B0.07N thin films were prepared on (100) Si substrates with the necessary c-axis out-of-plane orientation achieved through initial plasma treatment and subsequent layer growth. The resulting films exhibited strong polarization hysteresis, making them useful for integration with mainstream semiconductors.
APPLIED PHYSICS LETTERS
(2023)
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
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
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
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, 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
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
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
Nanoscience & Nanotechnology
Wanlin Zhu, Fan He, John Hayden, Zhongming Fan, Jung In Yang, Jon-Paul Maria, Susan Trolier-McKinstry
Summary: The study demonstrates the polarization wake-up process for ferroelectric switching in epitaxial Al0.93B0.07N films. As the remanent polarization grows, both reversible and irreversible Rayleigh coefficients rise substantially, indicating an increase in the concentration of mobile interfaces. Additionally, the low irreversible Rayleigh coefficient suggests high coercive fields in nitride ferroelectrics; the temperature and frequency dependence of Rayleigh coefficients reveal time-dependent and thermally activated processes.
ADVANCED ELECTRONIC MATERIALS
(2022)
Article
Nanoscience & Nanotechnology
Jie Zhang, Xiaoyang Chen, MingJian Ding, Jiaqiang Chen, Ping Yu
Summary: This study enhances the compositional inhomogeneity of relaxor ferroelectric thin films to improve their dielectric temperature stability. The prepared films exhibit a relatively high dielectric constant and a very low variation ratio of dielectric constant over a wide temperature range.
SCRIPTA MATERIALIA
(2024)
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
Nanoscience & Nanotechnology
Roberto Guido, Patrick D. Lomenzo, Md Redwanul Islam, Niklas Wolff, Maike Gremmel, Georg Schoenweger, Hermann Kohlstedt, Lorenz Kienle, Thomas Mikolajick, Simon Fichtner, Uwe Schroeder
Summary: The discovery of ferroelectricity in aluminum scandium nitride (Al1-xScxN) shows potential for technological applications in harsh environments and space-related memory applications. The high-temperature stability of piezoelectricity in aluminum nitride enhances the viability of this material. Through a combination of electrical and in-situ X-ray diffraction measurements, as well as transmission electron microscopy and energy-dispersive X-ray spectroscopy, the ferroelectric and material properties of 100 nm-thick Al0.72Sc0.28N have been studied up to 873 K. The findings demonstrate that Al0.72Sc0.28N can achieve high switching polarization and tunable coercive fields within a temperature range of 375 K from room temperature to 673 K.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Chemistry, Physical
He Li, Sadegh Askari, Jihao Wang, Niklas Wolff, Malte Behrens, Lorenz Kienle, Jan Benedikt
Summary: A noble-metal-free bifunctional electrocatalyst was developed through a facile strategy for rechargeable zinc-air batteries. The nitrogen-doped NiCo2O4 nanostructures on carbon paper exhibited enhanced electrocatalytic activities for oxygen evolution and reduction reactions. The plasma treatment optimized the N doping process without changing the morphology and specific surface area of the catalyst. The resulting air cathode showed improved stability and performance compared to noble-metal catalyst counterparts.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2023)
Article
Chemistry, Multidisciplinary
Niklas Wolff, Tudor Braniste, Helge Krueger, Sebastian Mangelsen, Redwanul Islam, Ulrich Schuermann, Lena M. Saure, Fabian Schuett, Sandra Hansen, Huayna Terraschke, Rainer Adelung, Ion Tiginyanu, Lorenz Kienle
Summary: This paper presents the synthesis and structural characterization of a hybrid beta-Ga2O3/ZnGa2O4 nanocomposite aero-network. Structural investigations reveal the transformation of the precursor aero-GaN(ZnO) network into hollow architectures composed of beta-Ga2O3 and ZnGa2O4 nanocrystals. The hybrid nanocomposite network demonstrates narrow band green light emission of ZnGa2O4 under UV light excitation and shows high initial capacities and exceptional rate performance for electrochemical applications.
Article
Nanoscience & Nanotechnology
Md Redwanul Islam, Georg Schoenweger, Niklas Wolff, Adrian Petraru, Hermann Kohlstedt, Simon Fichtner, Lorenz Kienle
Summary: In this study, the structural and electrical properties of Al0.72Sc0.28N thin films grown on different substrates were compared. It was found that using an epitaxial Pt electrode layer on a GaN/Al2O3 substrate significantly improved the leakage current and coercive field of the material. Furthermore, an all-epitaxial Al0.72Sc0.28N/Pt/GaN stack with a sharp interface thickness of less than 1 nm was demonstrated.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Physics, Applied
Katrin Pingen, Stefan Neuhaus, Niklas Wolff, Lorenz Kienle, Agne Zukauskaite, Elizabeth von Hauff, Alexander M. Hinz
Summary: The increasing demand for More than Moore devices requires epitaxy technology to keep up with the discovery and deployment of new semiconductors. An emerging technology for cost-effective, device-quality growth is magnetron sputter epitaxy, though detailed studies on the process itself remain scarce.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Georg Schoenweger, Niklas Wolff, Md Redwanul Islam, Maike Gremmel, Adrian Petraru, Lorenz Kienle, Hermann Kohlstedt, Simon Fichtner
Summary: This study investigates the ferroelectric switching characteristics of sub-5 nm thin Al0.74Sc0.26N films grown on different substrates. Significant progress has been made compared to previous wurtzite-type ferroelectrics, including record low switching voltages of 1 V, larger coercive field to breakdown field ratio on silicon substrates, and the first demonstration of true ferroelectric domains in wurtzite-type materials on the atomic scale. These findings pave the way for achieving analog switching necessary for neuromorphic computing in highly scaled devices.
