Article
Materials Science, Multidisciplinary
Rong Wang, Jianxing Xu, Shiyong Zhang, Ying Zhang, Penghui Zheng, Zhe Cheng, Lian Zhang, Feng-Xiang Chen, Xiaodong Tong, Yun Zhang, Wei Tan
Summary: Low-fluence neutron irradiation is a promising way to reduce the reverse leakage current in AlGaN/GaN heterostructures while maintaining other electronic properties almost unchanged. The mechanism involves the mobility of neutron scattered group-III interstitials, passivation of V-III-DLs, and escape of interstitials after saturation of passivation. This post-processing treatment offers a new approach for improving the electronic properties of AlGaN/GaN heterostructures grown by MOCVD on sapphire substrates.
JOURNAL OF MATERIALS CHEMISTRY C
(2021)
Article
Chemistry, Multidisciplinary
Sirui Feng, Zheyang Zheng, Yan Cheng, Yat Hon Ng, Wenjie Song, Tao Chen, Li Zhang, Kai Liu, Kai Cheng, Kevin J. Chen
Summary: This work presents a hybrid field-effect transistor (HyFET) using GaN and SiC semiconductors and proposes a methodology for improving epitaxy techniques. The researchers successfully grown high-quality heterostructure on a conventional surface and also studied a two-step biaxial strain-relaxation process.
ADVANCED MATERIALS
(2022)
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
Chemistry, Multidisciplinary
Isabel Streicher, Stefano Leone, Christian Manz, Lutz Kirste, Mario Prescher, Patrick Waltereit, Michael Mikulla, Rudiger Quay, Oliver Ambacher
Summary: In this study, AlScN/GaN heterostructures were grown and characterized to investigate the effect of diffusion of AlGaN on 2DEG confinement. The presence of interlayers and the growth temperature were found to significantly affect the sheet carrier density and electron mobility.
CRYSTAL GROWTH & DESIGN
(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
Materials Science, Multidisciplinary
Boxiang Yun, Shengrui Xu, Hongchang Tao, Xinhao Wang, Xu Liu, Qianlong Wu, Jincheng Zhang, Yue Hao
Summary: Unintentionally doped and Si-doped multi-channel AlGaN/GaN heterostructures grown on sapphire substrates were studied. The results showed that Si doping increased the surface roughness and formed V-shaped defects in the multi-channel AlGaN/GaN heterostructure. Transmission electron microscopy images revealed dislocation termination in the Si-doped multi-channel region. The formation mechanism of V-shaped defects and the principle of dislocation blocking in the Si-doped multi-channel region were analyzed.
Article
Crystallography
Hui-Tzu Chen, Victor V. Solovyev, Igor V. Kukushkin, Andreas Grosser, Thomas Mikolajick, Stefan Schmult
Summary: This study focuses on the wavelength-dependent conductivity of optically-induced 2-dimensional electron gases (2DEGs) in ultra-pure GaN/AlGaN heterostructures grown by Molecular Beam Epitaxy (MBE). The experiments show that only light with energies larger than the bandgap of GaN (3.4 eV) is able to generate a 2DEG, and the conductivity of the generated 2DEG depends on the number and energy of incident photons. Moreover, resonant absorption around the bandgap energy of GaN can be clearly observed at room temperature.
JOURNAL OF CRYSTAL GROWTH
(2022)
Article
Chemistry, Physical
Danhao Wang, Ding Wang, Peng Zhou, Mingtao Hu, Jiangnan Liu, Shubham Mondal, Tao Ma, Ping Wang, Zetian Mi
Summary: Through high-resolution X-ray photoelectron spectroscopy measurements, we discovered a thick oxide layer on ScAlN when exposed to air, which significantly affects its characterization and electronic structure evaluation. By excluding the possible impact from the surface oxide layer, the band alignment of Sc0.18Al0.82N/GaN can be accurately determined. Simulation results further demonstrate that the Sc0.18Al0.82N barrier layer offers excellent charge carrier confinement and a high density of two-dimensional electron gas (2DEG) at the heterostructure interface, crucial for high-performance GaN-based high electron mobility transistors (HEMTs).
APPLIED SURFACE SCIENCE
(2023)
Article
Chemistry, Multidisciplinary
Irene Manglano Clavero, Christoph Margenfeld, Jana Hartmann, Andreas Waag
Summary: This study investigates the influence of temperature and ammonia partial pressure on the morphology of GaN shell grown on GaN microfin cores. It is shown that growth above 1000 degrees C is determined by the competition between growth and decomposition, leading to material redistribution between different surfaces. Decomposition processes are found to strongly influence the vertical-to-lateral distribution of material during GaN growth on 3D structures. The findings emphasize the importance of understanding thermal decomposition processes and material redistribution for controlling and optimizing growth on these architectures.
CRYSTAL GROWTH & DESIGN
(2023)
Article
Nanoscience & Nanotechnology
Andreas Liudi Mulyo, Anjan Mukherjee, Ida Marie Hoiaas, Lyubomir Ahtapodov, Tron Arne Nilsen, Havard Hem Toftevaag, Per Erik Vullum, Katsumi Kishino, Helge Weman, Bjorn-Ove Fimland
Summary: This study successfully demonstrates the fabrication of flip-chip ultraviolet light-emitting diodes based on self-assembled GaN/AlGaN nanocolumns, using single-layer graphene as both a growth substrate and a transparent conducting electrode. The high crystalline quality of the nanocolumns and the presence of intrinsic GaN quantum disk are confirmed through detailed electron microscopy characterization. The optical emission characteristics reveal the absence of defect-related yellow emission and the presence of blue-shifted emission, attributed to quantum confinement and strain effects.
ACS APPLIED NANO MATERIALS
(2021)
Article
Physics, Applied
E. E. Yakimov, E. B. Yakimov
Summary: The effect of e-beam irradiation on stacking fault expansion in 4H-SiC was investigated. The study revealed that the range of e-beam influence on partial dislocation glide was limited and unaffected by dislocation length. Fixed point irradiation was used to separate carrier effects on kink formation and migration. The results imply a small migration barrier for kinks along Si-core 30 degrees partial dislocations in 4H-SiC.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Physics, Applied
Hao Yu, Vamsi Putcha, Uthayasankaran Peralagu, Ming Zhao, Sachin Yadav, Alireza Alian, Bertrand Parvais, Nadine Collaert
Summary: This study provides a comprehensive analysis of the leakage current mechanism in ion implantation isolation (I/I/I) regions of GaN high electron mobility transistors. The analysis reveals a positive correlation between the activation energy of R-sh and the energy level of the leakage path, and constructs the energy band diagram of the isolation region. A novel method to estimate the net active defect density caused by I/I/I is proposed, extracting net active defect densities in the GaN and AlGaN layers.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Chemistry, Physical
Dmitri S. S. Arteev, Alexei V. V. Sakharov, Wsevolod V. V. Lundin, Evgenii E. E. Zavarin, Andrey E. E. Nikolaev, Andrey F. F. Tsatsulnikov, Viktor M. M. Ustinov
Summary: This study investigates the influence of Fe segregation on the electrical properties of two-dimensional electron gas in AlGaN/AlN/GaN heterostructures. It was found that the concentration and mobility of the electron gas decrease with thinner channel layer thickness, leading to an increase in sheet resistance. The drop in mobility is attributed to a combination of ionized impurity scattering and various scattering effects.
Article
Chemistry, Multidisciplinary
Yinghao Wang, Lianxin Li, Tinghong Gao, Yue Gao, Yutao Liu, Quan Xie
Summary: The anisotropic differences in the induced growth of gallium nitride crystals were investigated using molecular dynamics simulations. The microstructural evolution and defect structure formation mechanism during anisotropic growth in crystals were studied in detail through solid-liquid modeling in three crystal orientations. Understanding the formation mechanism of gallium nitride crystals in different crystal orientations is crucial for optimizing crystal quality and enhancing device performance.
CRYSTAL GROWTH & DESIGN
(2023)
Article
Chemistry, Multidisciplinary
Daya Sagar Dhungana, Carlo Grazianetti, Christian Martella, Simona Achilli, Guido Fratesi, Alessandro Molle
Summary: The research introduces a concept of Xene heterostructure based on the epitaxial combination of silicene and stanene on Ag(111), demonstrating layer-by-layer growth and strong interactions between layers. The results represent a significant step towards filling the current gap in Xene heterostructures and may inspire new paths for atomic-scale materials engineering.
ADVANCED FUNCTIONAL MATERIALS
(2021)
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
Physics, Applied
Feng Wu, Jacob Ewing, Cheyenne Lynsky, Michael Iza, Shuji Nakamura, Steven P. DenBaars, James S. Speck
Summary: In this article, the authors used advanced characterization techniques to study the active region compositions, V-defect formation, and V-defect structure in green and red LEDs. They identified two types of V-defects, one that promotes hole injection and one that is believed to be deleterious to high-efficiency LEDs.
JOURNAL OF APPLIED 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
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)