Article
Nanoscience & Nanotechnology
Reet Chaudhuri, Zexuan Zhang, Huili Grace Xing, Debdeep Jena
Summary: By introducing indium in the GaN channel, the piezoelectric polarization difference across the heterointerface can be tuned, resulting in ultra-high carrier densities. These high-density InGaN/AlN 2DHGs have high mobilities at room temperature and do not freeze out at low temperatures.
ADVANCED ELECTRONIC MATERIALS
(2022)
Article
Physics, Applied
B. Ding, J. Jarman, M. J. Kappers, R. A. Oliver
Summary: By using STEM analysis, it was found that InGaN samples grown at lower temperatures exhibit microscale variations in the green-emitting surface, with brighter regions showing high density of gross-well width fluctuations, while dimmer regions have a more uniform thickness of InGaN QWs.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Physics, Applied
Zexuan Zhang, Jimy Encomendero, Reet Chaudhuri, Yongjin Cho, Vladimir Protasenko, Kazuki Nomoto, Kevin Lee, Masato Toita, Huili Grace Xing, Debdeep Jena
Summary: High-density 2DHGs are observed in undoped pseudomorphic GaN/AlN heterostructures on single-crystal AlN substrates, providing potential for high performance wide-bandgap p-channel transistors. The use of plasma-assisted molecular beam epitaxy allows for the achievement of record-high mobility and density of the 2DHGs, indicating significant improvements in 2D hole mobilities.
APPLIED PHYSICS LETTERS
(2021)
Article
Nanoscience & Nanotechnology
Ankit Udai, Swaroop Ganguly, Pallab Bhattacharya, Dipankar Saha
Summary: This study investigates the ultrafast carrier dynamics of bound states in In0.14Ga0.86N/GaN quantum wells using femtosecond transient absorption spectroscopy. It reveals that both the ground and excited states contribute to the overall dynamics, which can be decoupled in the absorption spectra and time-resolved dynamics.
Article
Chemistry, Multidisciplinary
Long Xu, Yuehan Cao, Tianwei Song, Caixia Xu
Summary: This work investigates the low-threshold resonant lasing emission in undoped and Mg-doped GaN thin films on sapphire substrates with interfacial design. The scattering cross-section of the periodic resonant structure is found to reduce the threshold and enhance the resonant lasing emission. Mg-doped GaN thin films show better lasing emission performance compared to undoped and Si-doped GaN thin films. The lasing energy level system and defect densities play a vital role in the lasing emission.
Article
Chemistry, Physical
Ashfaq Ahmad, Pawel Strak, Kamil Koronski, Pawel Kempisty, Konrad Sakowski, Jacek Piechota, Izabella Grzegory, Aleksandra Wierzbicka, Serhii Kryvyi, Eva Monroy, Agata Kaminska, Stanislaw Krukowski
Summary: This study uses ab initio calculations to determine the polarization difference in III-nitride compounds, showing varying polarization differences between different nitrides. In multi-quantum wells, electric fields are generated by well-barrier polarization difference, and the theoretical results are in good agreement with experimental measurements.
Article
Nanoscience & Nanotechnology
Wai Yuen Fu, Hoi Wai Choi
Summary: This report demonstrates a nanostructure configuration that produces spectral red-shifting by increasing the strain in the quantum wells through the formation of an inverted nanoconical-frustum array over the quantum wells. Experimental results show a red-shift of up to 7.6 nm in the photoluminescence spectrum when the proposed nanostructures are fabricated on InGaN/GaN quantum wells grown on a c-plane sapphire substrate with a nominal emission wavelength of around 560 nm.
ACS APPLIED NANO MATERIALS
(2021)
Article
Physics, Applied
H. Schuermann, G. Schmidt, F. Bertram, C. Berger, S. Metzner, P. Veit, A. Dadgar, A. Strittmatter, J. Christen
Summary: We report on the formation process of GaN/AlN quantum dots (QDs) and investigate the influence of the growth interruption time on their structural and optical properties. The results show that QDs develop from bulky GaN islands, which are influenced by threading dislocations and island morphology. The duration of growth interruption can be used to tune the emission wavelength of the QDs.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Chemistry, Physical
Ruishen Meng, Lino da Costa Pereira, Jean-Pierre Locquet, Valeri Afanas'ev, Geoffrey Pourtois, Michel Houssa
Summary: Through high-throughput calculations and evolutionary search method, 122 2D materials with potential ferromagnetism upon hole doping are identified, with some materials predicted to have Curie temperatures above 300K. These findings are important for understanding the properties of doped 2D ferromagnetic materials and enriching the family of 2D magnetic materials.
NPJ COMPUTATIONAL MATERIALS
(2022)
Article
Chemistry, Multidisciplinary
Gianfranco Sfuncia, Giuseppe Nicotra, Filippo Giannazzo, Bela Pecz, Gueorgui Kostov Gueorguiev, Anelia Kakanakova-Georgieva
Summary: In this study, a buckled GaN monolayer was obtained at the graphene/SiC interface under confinement using metal-organic chemical vapor deposition (MOCVD). Conductive atomic force microscopy (C-AFM) and scanning transmission electron microscopy (S/TEM) were used for characterization. The experiment confirmed the buckling parameter and revealed the atomic order of the GaN monolayer, providing new insights for predictive studies based on first-principles calculations.
Article
Nanoscience & Nanotechnology
Isaac G. Sonsona, Manuel Carrera, Miriam Mas-Montoya, Rafael S. Sanchez, Patricio Serafini, Eva M. Barea, Ivan Mora-Sero, David Curiel
Summary: Interfaces between photoactive perovskite layer and selective contacts are crucial for the performance of perovskite solar cells (PSCs). The properties of the interface can be modified using molecular interlayers between the halide perovskite and the transporting layers. This study introduces two structurally related molecules, TACB and TTAI, which can self-assemble through reciprocal hydrogen bond interactions. By combining these molecules with well-known hole transporting layers (HTLs), an improved photovoltaic performance was achieved in PSCs with inverted configuration.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Chemistry, Multidisciplinary
Can Zou, Zixuan Zhao, Mingjun Xu, Xingfu Wang, Qing Liu, Kai Chen, Longfei He, Fangliang Gao, Shuti Li
Summary: To address the issue of minority carrier storage time in bipolar transistors, a hot electron transistor (HET) has been proposed. This device offers high working speed and the ability to perform complex logic functions with just one component. A mixed-dimensional HET composed of GaN/AlN microwires, graphene (Gr), and Si has been demonstrated, which achieves high speed hot electrons by injecting electrons between GaN/AlN into graphene through F-N tunneling mechanism, allowing for ballistic transport and collection through low-barrier Si. The device exhibits a record DC gain of 16.2, collection efficiency close to the limit of 99.9% based on GHET, emitter current density of 68.7 A/cm2, high on/off current ratio of approximately 107, and wide current saturation range, making it suitable for potential applications as a power amplifier.
Article
Microscopy
T. J. O'Hanlon, F. C-P Massabuau, A. Bao, M. J. Kappers, R. A. Oliver
Summary: The study revealed that trench defects in InGaN quantum well structures can cause unusual emission behavior and the redshift in emission is influenced by the width of the trench and the prominence of the enclosed material.
Article
Chemistry, Multidisciplinary
Shasha Zhao, Huiliu Wang, Lixin Niu, Wenqi Xiong, Yunxu Chen, Mengqi Zeng, Shengjun Yuan, Lei Fu
Summary: Surface-enhanced Raman scattering (SERS) based on 2D semiconductors has rapidly advanced, and 2D gallium nitride (GaN) with highly polar Ga-N bonds is demonstrated to be a sensitive SERS platform due to strong dipole-dipole interactions and abundant density of states near its Fermi level.
Article
Physics, Applied
M. Lodari, O. Kong, M. Rendell, A. Tosato, A. Sammak, M. Veldhorst, A. R. Hamilton, G. Scappucci
Summary: A lightly strained germanium channel supports a high-mobility two-dimensional hole gas with low percolation density. This low-disorder system exhibits tunable fractional quantum Hall effects at low densities and low magnetic fields, making it a promising platform for fast and coherent quantum hardware.
APPLIED PHYSICS LETTERS
(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
Physics, Applied
Zexuan Zhang, Jashan Singhal, Shivali Agrawal, Eungkyun Kim, Vladimir Protasenko, Masato Toita, Huili Grace Xing, Debdeep Jena
Summary: Polarization-induced carriers are important for achieving high electrical conductivity in ultrawide bandgap semiconductor AlGaN. However, studies on these carriers in N-polar AlGaN are rare. This study observes and characterizes polarization-induced two-dimensional electron gases (2DEGs) in N-polar AlGaN/AlN heterostructures with varying Al content. The results provide valuable insights for designing high electron mobility transistors and UV photonic devices.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Jashan Singhal, Eungkyun Kim, Austin Hickman, Reet Chaudhuri, Yongjin Cho, Huili Grace Xing, Debdeep Jena
Summary: We conducted a study on the compositional dependence of electrical characteristics in AlxGa1-xN quantum well channel-based AlN/AlGaN/AlN high electron mobility transistors (HEMTs), with x values of 0.25, 0.44, and 0.58. The use of selectively regrown n-type GaN Ohmic contacts resulted in increased contact resistance with higher Al content in the channel. The DC HEMT device characteristics showed a progressive reduction in maximum drain current densities and a simultaneous decrease in threshold voltage with increasing x values.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Eungkyun Kim, Zexuan Zhang, Jimy Encomendero, Jashan Singhal, Kazuki Nomoto, Austin Hickman, Cheng Wang, Patrick Fay, Masato Toita, Debdeep Jena, Huili Grace Xing
Summary: Recent observations of high density polarization-induced electron gases in ultra-thin N-polar GaN layers on single-crystal AlN have allowed for the development of N-polar high electron mobility transistors (HEMTs) on AlN. These devices can take advantage of AlN's thermal and power handling capabilities, while also benefitting from N-polar structures like a strong back barrier. Experimental demonstrations of N-polar GaN/AlGaN/AlN HEMTs on single-crystal AlN substrates have shown promising performance, paving the way for RF electronics with excellent thermal management based on N-polar single-crystal AlN.
APPLIED PHYSICS LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Wenwen Zhao, Mohammad Javad Asadi, Lei Li, Reet Chaudhuri, Kazuki Nomoto, Huili Grace Xing, James C. M. Hwang, Debdeep Jena
Summary: This study demonstrates epitaxial AlN thin-film bulk acoustic resonators (FBARs) on SiC substrates with first-order thickness extensional modes of 15-17 GHz. The achieved quality factor Q(max) of approximately 443, electromechanical coupling coefficient k(eff)(2) of approximately 2.3%, and f center dot Q of approximately 6.65 THz figure of merit are among the highest in the Ku-band (12-18 GHz). The clean primary mode with a high quality factor allows these epitaxial AlN FBARs to be used in Ku-band acoustic filters with clean bands and steep rejection. Additionally, their compatibility with AlN/GaN/AlN quantum well high-electron-mobility transistors (QW HEMTs) allows for monolithic integration with HEMT low noise amplifiers (LNAs) and power amplifiers (PAs).
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Materials Science, Coatings & Films
Tobias Schwaigert, Salva Salmani-Rezaie, Matthew R. Barone, Hanjong Paik, Ethan Ray, Michael D. Williams, David A. Muller, Darrell G. Schlom, Kaveh Ahadi
Summary: Strain-engineering is used to tune the instabilities of incipient ferroelectrics. High-quality KTaO3 thin films are grown by molecular-beam epitaxy. Excess potassium and a combination of ozone and oxygen are supplied with the TaO2 (or tantalum) molecular beams to grow the films with atomically abrupt interfaces. Atomic force microscopy reveals atomic steps at the film surface. Reciprocal space mapping demonstrates coherent strain to the substrates when the films are thin enough.
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A
(2023)
Article
Materials Science, Coatings & Films
Thomas J. Smart, Felix V. E. Hensling, Dong Yeong Kim, Lena N. Majer, Y. Eren Suyolcu, Dominik Dereh, Darrell G. Schlom, Debdeep Jena, Jochen Mannhart, Wolfgang Braun
Summary: This work investigates the behavior of aluminum sources in oxide thermal laser epitaxy and identifies two distinct operating regimes. At high laser-beam fluences, the source emits reproducible fluxes independent of oxygen pressure. At lower beam fluences, the flux increases with increasing oxygen pressure due to suboxide formation. The study demonstrates reproducible rate control over a wide range and highlights the advantages of thermal laser epitaxy over oxide molecular-beam epitaxy in handling aluminum sources.
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A
(2023)
Review
Physics, Multidisciplinary
Javier Junquera, Yousra Nahas, Sergei Prokhorenko, Laurent Bellaiche, Jorge iniguez, Darrell G. Schlom, Long-Qing Chen, Sayeef Salahuddin, David A. Muller, Lane W. Martin, R. Ramesh
Summary: The past decade has witnessed significant progress in understanding emergent topological polar textures in oxide nanostructures, including vortices, skyrmions, merons, hopfions, dipolar waves, and labyrinthine domains. The discovery of low-dimensional ferroelectric oxide nanostructures has altered the perceived energy cost associated with the formation of these structures, allowing for manipulation of order parameters. This review provides a historical context, scientific description, and discussion of the potential applications and future challenges in this field.
REVIEWS OF MODERN PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Yao Yang, Yu-Tsun Shao, Jianbo Jin, Julian Feijoo, Inwhan Roh, Sheena Louisia, Sunmoon Yu, Maria V. Fonseca Guzman, Chubai Chen, David A. Muller, Hector D. Abruna, Peidong Yang
Summary: The design and synthesis of nanocatalysts with well-defined sizes, compositions, and structures have greatly enhanced our ability to control catalyst activity and selectivity for energy-related electrochemical reactions. By using operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM), the dynamic evolution of Cu nanocatalysts during CO2 electroreduction was observed, providing valuable insights into their active states. With further technical advancements, operando EC-STEM is expected to become a powerful electroanalytical method for studying nanoscale electrocatalysts at solid/liquid interfaces.
ACS SUSTAINABLE CHEMISTRY & ENGINEERING
(2023)
Article
Materials Science, Multidisciplinary
Megan E. Holtz, Elliot Padgett, Aaron C. Johnston-Peck, Igor Levin, David A. Muller, Andrew A. Herzing
Summary: Measuring local polar ordering is crucial for understanding ferroelectricity in thin films. The cepstral approach allows us to determine the local polar displacements that drive ferroelectricity from nanobeam electron diffraction patterns. Experimental results demonstrate that this technique achieves a precision of 1.1 pm in mapping polar displacements with nanometer resolution.
MICROSCOPY AND MICROANALYSIS
(2023)
Article
Materials Science, Multidisciplinary
Gustavo A. Alvarez, Joseph Casamento, Len van Deurzen, Md Irfan Khan, Kamruzzaman Khan, Eugene Jeong, Elaheh Ahmadi, Huili Grace Xing, Debdeep Jena, Zhiting Tian
Summary: Aluminum scandium nitride (AlScN) is gaining attention for its larger piezoelectric response compared to AlN, but alloying Sc with AlN reduces thermal conductivity. Self-heating limits power handling in AlScN devices, and we compared thermal conductivity of AlScN grown on different substrates.
MATERIALS RESEARCH LETTERS
(2023)
