Article
Engineering, Electrical & Electronic
A. Adhikari, A. Lysak, A. Wierzbicka, P. Sybilski, A. Reszka, B. S. Witkowski, E. Przezdziecka
Summary: In this study, the growth of CdO alloy using plasma-assisted molecular beam epitaxy method was investigated. The CdO alloy showed great potential for optoelectronic device fabrication. Structural and morphological analysis were conducted using X-ray diffraction and Atomic Force Microscopy techniques, while composition analysis was done by Energy-dispersive X-ray spectroscopy. The optical properties of thin films were studied using UV-Vis spectroscopy, and it was found that the bandgap of the films is affected by the incorporation of Mg2+ ions.
MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING
(2022)
Article
Materials Science, Multidisciplinary
P. V. Seredin, N. S. Buylov, D. L. Goloshchapov, S. A. Ivkov, E. P. Matyukhina, I. N. Arsentyev, A. V. Nashchekin, Sh. Sh. Sharofidinov, A. M. Mizerov, E. V. Pirogov, M. S. Sobolev
Summary: In this study, we investigated the effects of a non-polar m-plane sapphire substrate on the properties of HVPE growth and the characteristics of the GaN epitaxial film. We successfully obtained high-quality semipolar GaN samples on the m-sapphire substrate and determined their structural and optical properties. The optimization of the technological methodology may present a promising approach for the growth of high-quality GaN structures on large area m-sapphire substrates.
Article
Chemistry, Physical
Mansi Agrawal, Anubha Jain, Vishakha Kaushik, Akhilesh Pandey, B. R. Mehta, R. Muralidharan
Summary: In this study, catalyst-free GaN nanowires were grown on Si (111) substrates by plasma-assisted molecular beam epitaxy, followed by the deposition of a few layers of MoS2 by chemical vapor deposition. The morphology and vibrational properties of the MoS2/GaN nanowires on Si (111) substrates were analyzed using scanning electron microscopy and Raman spectroscopy. The results indicate the potential of MoS2/GaN nanowires heterojunction for future optoelectronic devices due to their exceptional structural and vibrational properties.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Nanoscience & Nanotechnology
Fernando M. de Oliveira, Andrian V. Kuchuk, Petro M. Lytvyn, Cosmin Romanitan, Hryhorii V. Stanchu, Marcio D. Teodoro, Morgan E. Ware, Yuriy I. Mazur, Gregory J. Salamo
Summary: This article discusses the impact of uncontrolled electron accumulation layer near the surface of InN thin films on the development of narrow-bandgap optoelectronics, and proposes a method to regulate it by modulating the surface of InN grown on GaN(001). By increasing the surface-to-volume ratio, the surface carrier concentration can be significantly reduced. Contrary to the previous belief, the controlled changes are not caused by donor-type surface states contributing to conduction band electrons.
ACS APPLIED NANO MATERIALS
(2023)
Article
Physics, Applied
Ping Wang, Ding Wang, Shubham Mondal, Zetian Mi
Summary: In this study, robust ferroelectricity was demonstrated in single-crystalline thin films. The crystallographic alignment was confirmed using x-ray diffraction measurements. The highly uniform coercive field and remnant polarization were observed in the nearly lattice-matched heterostructure. The reliability of the ferroelectricity was systematically characterized and showed negligible degradation after a large number of switching cycles. This research provides a feasible pathway for fully epitaxial integration of ferroelectricity into nitride heterostructures, with important applications in various fields.
APPLIED PHYSICS LETTERS
(2022)
Article
Crystallography
Amalia Fernando-Saavedra, Steven Albert, Ana Bengoechea-Encabo, Achim Trampert, Mengyao Xie, Miguel A. Sanchez-Garcia, Enrique Calleja
Summary: Non-polar m-plane GaN films were grown on & gamma;-LiAlO2 (100) substrates using a two-step process that involved coalescence of GaN nanocolumns obtained from a GaN buffer. Transmission electron microscopy data showed a significant reduction in extended defects density in the coalesced film compared to the initial GaN buffer, likely due to a filter effect during the regrowth process. Low temperature photoluminescence spectra confirmed this reduction in defects, with a decrease in stacking faults emission peaks and a dominant donor-bound excitonic emission at 3.472 eV.
JOURNAL OF CRYSTAL GROWTH
(2023)
Article
Nanoscience & Nanotechnology
Isha Verma, Sedighe Salimian, Valentina Zannier, Stefan Heun, Francesca Rossi, Daniele Ercolani, Fabio Beltram, Lucia Sorba
Summary: The study optimized the morphology of free-standing 2D InSb nanoflags (NFs), increasing their lateral size while maintaining defect-free zinc blend crystal structure, stoichiometric composition, and relaxed lattice parameters. These NFs were found large enough to fabricate Hall-bar contacts for precise electrical characterization, resulting in a measured electron mobility of approximately 29,500 cm(2) /(V s), the highest reported for free-standing 2D InSb nanostructures in literature. The study envisions the use of 2D InSb NFs for the fabrication of advanced quantum devices.
ACS APPLIED NANO MATERIALS
(2021)
Article
Chemistry, Physical
P. M. Lytvyn, S. P. Minor, A. Kuchuk, S. Kondratenko, Yu Mazur, Yu Maidaniuk, M. Benamara, M. E. Ware, S. Wu, Zh M. Wang, G. J. Salamo
Summary: This study investigates the effects of growth rate on the structural and electrical properties of InN nanostructures, showing that changes in growth rate can influence the crystal facet structures and residual electron concentration of the nanostructures.
APPLIED SURFACE SCIENCE
(2021)
Article
Chemistry, Multidisciplinary
Lei Liu, Ruixian Yu, Guodong Wang, Mingsheng Xu, Shouzhi Wang, Hongdi Xiao, Xiaobo Hu, Lei Zhang, Xiangang Xu
Summary: A self-standing porous GaN crystal film was fabricated for the first time using a high-temperature annealing method, showing reduced stress and improved crystal quality. The theoretical calculations and experimental results demonstrate the potential of high-temperature annealing porous templates for growing high-quality GaN crystals.
Article
Nanoscience & Nanotechnology
Mario Fabian Zscherp, Silas Aurel Jentsch, Marius Johannes Mueller, Vitalii Lider, Celina Becker, Limei Chen, Mario Littmann, Falco Meier, Andreas Beyer, Detlev Michael Hofmann, Donat Josef As, Peter Jens Klar, Kerstin Volz, Sangam Chatterjee, Joerg Schoermann
Summary: The lack of internal polarization fields in cubic group-IIInitrides makes them promising arsenic-free contenders for next-generation high-performance electronic and optoelectronic applications. In this study, cubic In x Ga1-x N films were successfully fabricated on c-GaN/AlN/3C-SiC/Si template substrates using plasma-assisted molecular beam epitaxy (PAMBE), effectively closing the miscibility gap. The films exhibited a CuPt-type ordering in highly alloyed regions, resulting in a spectrally narrower emission compared to statistically disordered zincblende materials.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Crystallography
Yun Lai, Ding Wang, Qinhao Kong, Xiaoju Luo, Jinfeng Tang, Rensuo Liu, Fei Hou, Xianying Wang, Troy J. Baker
Summary: Four-inch semi-insulating free-standing gallium nitride (GaN) wafers grown by hydride vapor phase epitaxy (HVPE) with carbon doping were obtained through a self-separated process. The as-grown wafer thickness can reach 900 mu m without cracks, and x-ray diffraction rocking curves show low FWHMs. The measured resistivity was greater than 10(10) Omega-cm.
JOURNAL OF CRYSTAL GROWTH
(2021)
Article
Chemistry, Multidisciplinary
Karol Olszewski, Marta Sobanska, Vladimir G. Dubrovskii, Egor D. Leshchenko, Aleksandra Wierzbicka, Zbigniew R. Zytkiewicz
Summary: This study focused on the growth of GaN nanowires on Si(111) substrates using plasma-assisted molecular beam epitaxy, specifically investigating the orientation and growth rate of the nanowires. The researchers found that vertically aligned nanowires grew faster and produced more regular ensembles compared to inclined nanowires. These densely packed ensembles of vertically aligned GaN nanowires on ZrN/Si(111) surfaces are highly relevant for device applications.
Article
Nanoscience & Nanotechnology
Bo Meng, Borislav Hinkov, Nolwenn Marie L. Biavan, Hanh T. Hoang, Denis Lefebvre, Maxime Hugues, David Stark, Martin Franckie, Almudena Torres-Pardo, Julen Tamayo-Arriola, Miguel M. Bajo, Adrian Hierro, Gottfried Strasser, Jerome Faist, Jean M. Chauveau
Summary: ZnO-based heterostructures are considered promising candidates for optoelectronic devices in the infrared and terahertz spectral domains due to their unique material properties. Experimental observation has shown that ZnO/MgxZn1-xO quantum cascade structures can exhibit terahertz intersubband electroluminescence, which is significant for the realization of ZnO-based terahertz quantum cascade lasers.
Article
Chemistry, Multidisciplinary
Mario F. Zscherp, Nils Mengel, Detlev M. Hofmann, Vitalii Lider, Badrosadat Ojaghi Dogahe, Celina Becker, Andreas Beyer, Kerstin Volz, Joerg Schoermann, Sangam Chatterjee
Summary: This study successfully optimized the quality of c-GaN epitaxial layers by introducing pre-growth treatments and buffer layers, achieving nearly perfect crystallinity and smooth surfaces and interfaces. The optimized growth parameters resulted in extremely small surface roughness and very limited stacking fault densities in phase pure c-GaN layers. The high structural quality of the epitaxial layers was further confirmed through photoluminescence spectroscopy.
CRYSTAL GROWTH & DESIGN
(2022)
Article
Crystallography
Lin Zhang, Zeren Wang, Jiejun Wu, Tong Han, Fang Liu, Xingyu Zhu, Tongjun Yu
Summary: In this study, high quality semi-polar GaN layers were fabricated on m-plane sapphire templates using vertical hydride vapor phase epitaxy system. The in-plane epitaxial relationships between GaN and sapphire substrate were determined, and the crystalline anisotropies were shown to be associated with crystal quality and surface defects.
JOURNAL OF CRYSTAL GROWTH
(2022)
Article
Physics, Condensed Matter
Mylene Sauty, Natalia Alyabyeva, Cheyenne Lynsky, Yi Chao Chow, Shuji Nakamura, James S. Speck, Yves Lassailly, Alistair C. H. Rowe, Claude Weisbuch, Jacques Peretti
Summary: In this study, scanning tunneling electroluminescence microscopy was used to investigate the unique radiative recombination properties near a defect in an InGaN/GaN quantum well. The results revealed intense emission peaks at higher energies close to the defect edges, which were not visible in the macrophotoluminescence spectrum. The quantitative information obtained from fitting the local tunneling electroluminescence spectra provided important insights into carrier localization in the quantum well.
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
(2023)
Article
Optics
Panpan Li, Hongjian Li, Yifan Yao, Kai Shek Qwah, Mike Iza, James S. Speck, Shuji Nakamura, Steven P. Denbaars
Summary: In this work, we demonstrate the vertical integration of nitride-based blue/green micro-light-emitting diode (mu LED) stacks with independent junction control using a hybrid tunnel junction (TJ). The hybrid TJ was grown by metal-organic chemical vapor deposition (p + GaN) and molecular-beam epitaxy (n + GaN). Different junction diodes were able to generate uniform blue, green, and blue/green emissions. The peak external quantum efficiency (EQE) of the TJ blue mu LEDs and green mu LEDs with indium tin oxide contact were 30% and 12%, respectively. Carrier transportation between different junction diodes was discussed. This work suggests a promising approach for vertical mu LED integration to enhance the output power of single LED chips and monolithic mu LEDs with different emission colors and independent junction control.
Article
Engineering, Electrical & Electronic
M. Ikram Md Taib, M. A. Ahmad, E. A. Alias, A. Alhassan, I. A. Ajia, M. M. Muhammed, I. S. Roqan, S. P. DenBaars, J. S. Speck, S. Nakamura, N. Zainal
Summary: In-surfactant was introduced during the growth of high temperature GaN quantum barriers and GaN interlayer in InGaN/GaN green LEDs. Results showed that the introduction of In-surfactant improved LED growth, particularly in the GaN interlayer. It improved the morphology of the interlayer, allowed it to serve as a good surface growth, and effectively improved the multi-quantum wells. Moreover, the introduction of In-surfactant shifted the emission wavelength towards red, reduced the forward voltage of the LEDs, and allowed faster carrier decay lifetime.
SEMICONDUCTOR SCIENCE AND TECHNOLOGY
(2023)
Article
Nanoscience & Nanotechnology
Matthew S. Wong, Aditya Raj, Hsun-Ming Chang, Vincent Rienzi, Feng Wu, Jacob J. Ewing, Emily S. Trageser, Stephen Gee, Nathan C. Palmquist, Philip Chan, Ji Hun Kang, James S. Speck, Umesh K. Mishra, Shuji Nakamura, Steven P. DenBaars
Summary: The electrical performance of III-nitride blue micro-light-emitting diodes (mu LEDs) with different tunnel junction (TJ) architectures grown by metalorganic chemical vapor deposition is investigated. The introduction of AlGaN layer above the n-side of the TJ layer improves the current density-voltage characteristic and the effects of AlGaN/GaN superlattices are examined. The band diagram simulation shows that a net positive polarization charge is formed at the AlGaN/GaN interface, leading to a reduction in tunneling distance and an increase in tunneling probability. Additionally, the proposed AlGaN-enhanced TJ design significantly enhances the wall-plug efficiency of mu LEDs.
Article
Physics, Applied
Panpan Li, Hongjian Li, Yunxuan Yang, Matthew S. Wong, Mike Iza, Michael J. Gordon, James S. Speck, Shuji Nakamura, Steven P. DenBaars
Summary: This article presents high-performance 10 x 10 μm InGaN amber micro-size LEDs. At 15 A cm(-2), the InGaN micro LEDs exhibit a single emission peak at 601 nm. The peak external quantum efficiency (EQE) and wall-plug efficiency are 5.5% and 3.2%, respectively. Compared to the 100 x 100 μm InGaN red micro LEDs, the 10 x 10 μm InGaN red micro LEDs maintain a similar EQE value with the same efficiency droop. These results highlight the higher efficiency potential of InGaN materials compared to common AlInGaP materials for the ultra-small size red micro LEDs required by augmented reality and virtual reality displays.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Wan Ying Ho, Yi Chao Chow, Shuji Nakamura, Jacques Peretti, Claude Weisbuch, James S. Speck
Summary: Electron emission spectroscopy was performed on metalorganic chemical vapor deposition grown p-n(-)-n(+) junctions with p-thicknesses ranging from 50 to 300 nm, doped with [Mg] = 3.5 x 10(19) cm(-3). By measuring the decreasing emitted electron intensity from a cesiated p-GaN surface with increasing p-thickness, we were able to extract the minority carrier diffusion length of electron in p-type GaN, L-e = 2663 nm. The measured value is in good agreement with literature reported values. The extrapolated electron current at the n(-) region p-GaN interface is in reasonable agreement with the simulated electron current at the interface.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Fikadu Alema, Takeki Itoh, William Brand, Andrei Osinsky, James S. Speck
Summary: We investigated the controllable nitrogen doping of beta-Ga2O3 using ammonia diluted in nitrogen as a source of active nitrogen. The study looked at the effects of flow rate and substrate temperature on the doping efficiency and reproducibility. By increasing the flow rate of NH3/N-2, the nitrogen impurities incorporated into beta-Ga2O3 increased linearly. The presence of hydrogen in the film accompanied the nitrogen doping at low substrate temperatures.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Y. C. Chow, C. Lynsky, S. Nakamura, S. P. DenBaars, C. Weisbuch, J. S. Speck
Summary: Efficiency droop at high current densities is a common problem for InGaN-based LEDs, especially for conventional c-plane devices. This study introduces a method to reduce the internal electric fields in c-plane quantum wells by using doped barriers, which allows for a thick active region design and leads to improved LED performance.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Optics
J. Mickevic, E. Valkiunaite, Z. Podlipskas, K. Nomeika, S. Nargelas, G. Tamulaitis, Y. C. Chow, S. Nakamura, J. S. Speck, C. Weisbuch, R. Aleksieju
Summary: The dynamics of two distinct bands in non-polar m-plane InGaN/GaN multiple quantum wells (MQWs) were investigated using PL, CL, and DT spectroscopy. The shift in peak emission wavelength with increasing excitation was caused by competition between these bands. DT measurements attributed the high-energy PL band to optical transitions between ground QW states, while the low-energy PL band was associated with recombination of localized carriers. CL measurements confirmed the dispersion of deep localized states and suggested small-scale disorder. PL measurements showed that localized states are highly sensitive to indium content and structural parameters. Temperature-dependent PL studies revealed strong carrier-phonon interaction.
JOURNAL OF LUMINESCENCE
(2023)
Article
Nanoscience & Nanotechnology
Panpan Li, Hongjian Li, Yifan Yao, Norleakvisoth Lim, Matthew Wong, Mike Iza, Michael J. Gordon, James S. Speck, Shuji Nakamura, Steven P. DenBaars
Summary: We have shown a significant improvement in the quantum efficiency of InGaN red micro-light-emitting diodes (mu LEDs). The peak external quantum efficiency (EQE) of the packaged 80 x 80 mu m(2) InGaN red mu LEDs increased to 6.0% at 12A/cm(2), indicating a significant advancement in the efficiency exploration of InGaN red mu LEDs. The enhancement in EQE is attributed to improved quantum efficiency, confirmed by electron-hole wavefunction overlap and photoluminescence intensity ratio analysis. Additionally, ultrasmall 5x 5 mu m(2) InGaN red mu LEDs were obtained with a high peak EQE of 4.5%.
Article
Nanoscience & Nanotechnology
Takeki Itoh, Akhil Mauze, Yuewei Zhang, James S. Speck
Summary: Continuous Si doping in beta-Ga2O3 epitaxial films was achieved using plasma-assisted molecular beam epitaxy with a valved effusion cell for the Si source. Secondary ion mass spectroscopy results indicated flat and sharply turned Si doping profiles in beta-Ga2O3. The Si doping concentration could be controlled by adjusting the cell temperature or the valve aperture of the Si effusion cell. High crystal quality and smooth surface morphologies were observed in Si-doped beta-Ga2O3 films grown on (010) and (001) substrates. The Si-doped (001) beta-Ga2O3 epitaxial film exhibited an electron mobility of 67 cm(2)/Vs at a Hall concentration of 3 x 10(18) cm(-3).
Article
Psychology, Developmental
Erin P. Vaughan, Julianne S. Speck, Paul J. Frick, Toni M. Walker, Emily L. Robertson, James V. Ray, Tina D. Wall Myers, Laura C. Thornton, Laurence Steinberg, Elizabeth Cauffman
Summary: Research on proactive and reactive aggression in adolescents and young adults found that these two types of aggression have unique developmental trajectories and distinct covariates. Proactive aggression was influenced by callous-unemotional traits, while reactive aggression was predicted by impulsivity. These findings highlight the importance of considering the specific factors associated with each type of aggression in understanding and addressing aggressive behaviors.
DEVELOPMENT AND PSYCHOPATHOLOGY
(2023)
Article
Physics, Applied
Wan Ying Ho, Cameron W. Johnson, Tanay Tak, Mylene Sauty, Yi Chao Chow, Shuji Nakamura, Andreas Schmid, Jacques Peretti, Claude Weisbuch, James S. Speck
Summary: In this study, the lateral distribution of the junction current in an electrical biased p-n GaN diode was measured using electron emission microscopy with a low-energy electron microscope. The vacuum level on the diode surface was reduced by cesium deposition to achieve negative electron affinity, allowing emitted overflow electrons on the biased diode surface to be imaged for their spatial distribution. The obtained results were compared with Joyce and Wemple's analytical solutions [J. Appl. Phys. 41, 3818 (1970)] and showed a good match.
APPLIED PHYSICS LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Wan Ying Ho, Abdullah I. Alhassan, Cheyenne Lynsky, Yi Chao Chow, Daniel J. Myers, Steven P. DenBaars, Shuji Nakamura, Jacques Peretti, Claude Weisbuch, James S. Speck
Summary: Using electron emission spectroscopy, researchers measured and analyzed the energy distribution of vacuum emitted electrons from electrically driven InGaN/GaN green light emitting diodes (LEDs) with and without a prewell superlattice (SL). They discovered a high-energy upper valley peak at approximately 1.7 eV above the I' valley in samples without a prewell SL, which is attributed to trap-assisted Auger recombination (TAAR). The absence of this peak in the sample with a prewell SL suggests the gettering of unidentified impurities that act as TAAR centers.
Article
Physics, Applied
Saulius Marcinkevicius, Jacob Ewing, Rinat Yapparov, Feng Wu, Shuji Nakamura, James S. Speck
Summary: Hole injection through V-defect sidewalls into all quantum wells can increase the efficiency of long wavelength GaN light emitting diodes, allowing for population of all wells in a multiple QW structure.
APPLIED PHYSICS LETTERS
(2023)
