Article
Physics, Condensed Matter
Tao Zhang, Yifan Li, Qian Cheng, Zhiguo Hu, Jinbang Ma, Yixin Yao, Chenxia Cui, Yan Zuo, Qian Feng, Yachao Zhang, Hong Zhou, Jing Ning, Chunfu Zhang, Jincheng Zhang, Yue Hao
Summary: By adjusting the growth parameters and thermal treatment, we achieved the crystal phase transition from ε-Ga2O3 to β-Ga2O3 films, and successfully obtained the target films at 400 degrees Celsius.
SUPERLATTICES AND MICROSTRUCTURES
(2021)
Article
Engineering, Electrical & Electronic
Jiayan Chu, Quan Wang, Lijuan Jiang, Chun Feng, Wei Li, Hongxin Liu, Hongling Xiao, Xiaoliang Wang
Summary: A high quality Al0.25Ga0.75N/GaN HEMT structure was grown on a 2-inch GaN substrate using MOCVD, with a two-stage heating method proposed for surface stabilization to protect the GaN substrate. The resulting structure exhibited a low RMS roughness and dislocation density, and a record high 2DEG mobility attributed to the smooth surface and good crystal quality.
JOURNAL OF ELECTRONIC MATERIALS
(2021)
Article
Materials Science, Multidisciplinary
Chunlei Zhao, Teng Jiao, Wei Chen, Zeming Li, Xin Dong, Zhengda Li, Zhaoti Diao, Yuantao Zhang, Baolin Zhang, Guotong Du
Summary: This paper reports the preparation of homoepitaxial Si-doped Ga2O3 film using MOCVD, showing high crystalline quality and n-type properties suitable for Ga2O3 power devices.
Article
Chemistry, Multidisciplinary
Edgar Gutierrez-Fernandez, Alberto D. Scaccabarozzi, Aniruddha Basu, Eduardo Solano, Thomas D. Anthopoulos, Jaime Martin
Summary: The study demonstrates that using the commonly used nonfullerene acceptor BTP-4F can achieve organic thin-film transistors with high electron mobility, opening up new possibilities in the field of organic electronics. Efficient charge transport is linked to highly ordered crystalline structure, providing a new approach for exploring high mu(e) organic materials.
Article
Materials Science, Ceramics
Tao Zhang, Yifan Li, Qian Cheng, Zhiguo Hu, Jinbang Ma, Yixin Yao, Yan Zuo, Qian Feng, Yachao Zhang, Hong Zhou, Jing Ning, Chunfu Zhang, Jincheng Zhang, Yue Hao
Summary: In this study, β-Ga2O3 films were successfully deposited on sapphire substrates using pulsed MOCVD, and the effects of different O-2 pulse times on the growth and properties were investigated. The results showed that the film deposited with a 0.2-minute O-2 pulse had the best crystalline quality and stable photoelectric performance.
CERAMICS INTERNATIONAL
(2022)
Article
Materials Science, Multidisciplinary
Tao Zhang, Qian Cheng, Zhiguo Hu, Yifan Li, Jinbang Ma, Yixin Yao, Yan Zuo, Qian Feng, Yachao Zhang, Hong Zhou, Jing Ning, Chunfu Zhang, Jincheng Zhang, Yue Hao
Summary: Ga2O3 films were deposited on non-polar sapphire and epi-GaN substrates at low temperature by MOCVD. The film quality was found to be the best on r-plane sapphire substrate, while the Ga2O3 film on GaN substrate had better crystalline quality compared to that on a-plane sapphire substrate.
Article
Physics, Applied
F. Egyenes, F. Gucmann, A. Rosova, E. Dobrocka, K. Husekova, F. Hrubisak, J. Keshtkar, M. Tapajna
Summary: A significant anisotropy in electrical conductance was observed in Si-doped alpha-Ga2O3/sapphire samples grown via liquid-injection metal organic chemical vapor deposition. X-ray diffraction (XRD) revealed the presence of (010) beta-Ga2O3 in addition to epitaxial alpha-Ga2O3. Various characterization techniques confirmed the formation of (010) beta-Ga2O3 filaments in undoped alpha-Ga2O3 film. Conductive AFM and current-voltage measurements confirmed the higher conductivity along the [2(1)(1)0] alpha-Ga2O3 direction compared to [0001] alpha-Ga2O3 direction, attributed to the presence of beta-Ga2O3 filaments.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2023)
Article
Nanoscience & Nanotechnology
Tao Zhang, Qian Cheng, Yifan Li, Zhiguo Hu, Jinbang Ma, Yixin Yao, Yuxuan Zhang, Yan Zuo, Qian Feng, Yachao Zhang, Hong Zhou, Jing Ning, Chunfu Zhang, Jincheng Zhang, Yue Hao
Summary: In this study, beta-Ga2O3 films were deposited on (-201) homo-substrates using MOCVD method. It was found that the Ga source flow rate significantly influenced the surface morphology, and a relatively flat surface was obtained with appropriate TEGa and O-2 flow rates. The substrate morphology can be greatly improved by cleaning and thermal annealing, which promotes the surface flatness of the epilayer. Insertion of a buffer layer and optimization of growth conditions also contribute to achieving a higher surface flatness.
SCRIPTA MATERIALIA
(2022)
Article
Chemistry, Multidisciplinary
Pheiroijam Pooja, Chun Che Chien, Albert Chin
Summary: This paper presents the first nanocrystalline SnON (7.6% nitrogen content) nanosheet n-type Field-Effect Transistor (nFET) with high effective mobility (μeff) of 357 and 325 cm(2)/V-s at electron density (Qe) of 5 x 10(12) cm(-2) and ultra-thin body thickness (T-body) of 7 nm and 5 nm, respectively. The high μeff values are attributed to the lower effective field (E-eff) and higher dielectric constant (κ) in the channel material, as well as the overlap of large radius s-orbitals, low effective mass (m(e)*) and low polar optical phonon scattering. The SnON nFETs with high μeff and quasi-2D thickness have potential applications in monolithic 3D integrated circuits (ICs) and embedded memory for 3D biological brain-mimicking structures.
Article
Materials Science, Ceramics
Yao Wang, Jiale Li, Tao Zhang, Wenji Li, Qian Feng, Yachao Zhang, Chunfu Zhang, Jincheng Zhang, Yue Hao
Summary: In this study, the quality of β-Ga2O3 film on sapphire substrates was optimized using pulsed metal-organic chemical vapor deposition (MOCVD) technology with indium pulse-assisted. The addition of indium atoms effectively improved the surface flatness and optical properties of the film.
CERAMICS INTERNATIONAL
(2023)
Article
Materials Science, Multidisciplinary
Pheiroijam Pooja, Chien Chun Che, Shi-Hao Zeng, Yu Chieh Lee, Te-Jui Yen, Albert Chin
Summary: This study reports record high field-effect mobility (mu(FE)) thin film transistors (TFTs) based on SnON channel layers with 5 and 7 nm thickness. The SnON TFT device with nitrogen content achieves a record high mu(FE) of 299 cm(2) V-1 s(-1) at 7 nm thickness and 277 cm(2) V-1 s(-1) at 5 nm thickness, compared to SnO2 with mu(FE) of 211 cm(2) V-1 s(-1). The high mu(FE) is attributed to the lower effective mass of electrons in the conduction band and the reduced defect trap densities in SnON through nitrogen alloying. The nanosheet SnON TFTs show potential for applications in embedded DRAM and monolithic 3D integrated circuits (ICs).
ADVANCED MATERIALS TECHNOLOGIES
(2023)
Article
Chemistry, Physical
Artem M. Makarevich, Alexander G. Sobol, Ilia I. Sadykov, Dmitrii Sharovarov, Vadim A. Amelichev, Dmitry M. Tsymbarenko, Olga Boytsova, Andrey R. Kaul
Summary: Epitaxial VO2 films with ideal composition, dense structure, and superior functional properties were successfully obtained using water-assisted MOCVD from vanadyl hexafluoroacetylacetonate on r-sapphire substrates under optimized conditions. The films exhibit intense optical switch properties in the IR region and unique metal-insulator transition characteristics, making them promising for highly sensitive and ultrafast switches in optical, electronic, and biomedical devices.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Physics, Applied
Yongjian Ma, Xiaodong Zhang, Junshuai Li, Xu Cao, Tao He, Li Zhang, Wenbo Tang, Kun Xu, Yaming Fan, Yong Cai, Houqiang Fu, Baoshun Zhang
Summary: By controlling the growth temperature and O-2 flow rate, the lateral epitaxial growth rate of beta-Ga2O3 nanowires can be increased, which is related to reaction kinetics and parasitic reactions. Additionally, a growth model proposed in the study helps explain the morphology changes of nanowires under different growth conditions.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Crystallography
Junhee Lee, Honghyuk Kim, Lakshay Gautam, Manijeh Razeghi
Summary: The high thermal stability of kappa gallium oxide grown on c-plane sapphire substrate by metal organic chemical vapor deposition was demonstrated. The material showed high electrical resistivity when doped with silicon, but significantly improved conductivity when doped with both indium and silicon. This work provides a pathway for utilizing kappa gallium oxide possessing superior electrical characteristics.
Article
Chemistry, Physical
Tao Zhang, Yifan Li, Yachao Zhang, Qian Feng, Jing Ning, Chunfu Zhang, Jincheng Zhang, Yue Hao
Summary: Beta-Ga2O3 films were grown on epi-GaN/sapphire substrates at different temperatures by low pressure MOCVD. The crystal structure, surface morphology, and element chemical state were influenced by temperature. Higher temperature led to improved crystal quality and surface morphology, as confirmed by XRD, AFM, and SEM analyses.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Engineering, Electrical & Electronic
R. M. Cadena, D. R. Ball, E. X. Zhang, S. Islam, A. Senarath, M. W. McCurdy, E. Farzana, J. S. Speck, N. Karom, A. O'Hara, B. R. Tuttle, S. T. Pantelides, A. F. Witulski, K. F. Galloway, M. L. Alles, R. A. Reed, D. M. Fleetwood, R. D. Schrimpf
Summary: Low-energy ion-induced breakdown and single event burnout (SEB) were observed in beta-gallium oxide (beta-Ga2O3) Schottky diodes at voltages lower than expected. Different responses were observed for alpha particles, Cf-252, and heavy-ion irradiation. TCAD simulations explained the breakdown as a result of ion strikes and defect-driven breakdown due to displacement-damage-induced defects in beta-Ga2O3. First-principles calculations showed the formation of less resistive defect clusters that can lead to destruction at reduced voltages.
IEEE TRANSACTIONS ON NUCLEAR SCIENCE
(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
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)