Article
Nanoscience & Nanotechnology
Xiaodong Hao, Xishuo Zhang, Benyao Sun, Deqiang Yin, Hailiang Dong, Jiahui Wang, Biao Huang, Yang Xu, Hengsheng Shan, Shufang Ma, Chunlin Chen, Bingshe Xu
Summary: Using the InGaN/GaN quantum wells model system, this study investigated the interfacial polarization and its synergic effect with the built-in electric field in solar cells. The generated polarized electric field was consistent with the built-in electric field on different surfaces, favoring electron-hole separation efficiency. Additionally, high-quality InGaN/GaN quantum wells were successfully grown on a specific surface. This atomic-scale investigation provides a fundamental understanding of the polarization-induced electric field and its interaction with the built-in electric field, applicable to polar material-based solar cells.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Optics
Mirsaeid Sarollahi, Pijush K. Ghosh, Manal A. Aldawsari, Shiva Davari, Malak Refaei, Reem Alhelais, Yuriy Mazur, Morgan E. Ware
Summary: Graded InGaN structures were designed by increasing indium composition, forming a Zig-Zag quantum well with broadband emission shifting to lower energies. The lowest energy band-to-band transition shifts noticeably with higher indium content, making the structure useful in optoelectronic devices.
JOURNAL OF LUMINESCENCE
(2021)
Article
Materials Science, Ceramics
Hyun Jeong, Heedae Kim, Mun Seok Jeong
Summary: The optical characteristics of nonplanar a-plane and c-plane InGaN/GaN MQWs were studied, and it was found that the a-plane MQWs have a higher integrated PL intensity and a more uniform distribution of PL intensity in two-dimensional space compared to the c-plane MQWs. These results indicate that nonpolar a-plane InGaN/GaN MQWs have superior optical performance compared to typical c-plane MQWs.
CERAMICS INTERNATIONAL
(2023)
Article
Nanoscience & Nanotechnology
Di Jiang, Penggang Li, Bin Liu, Kai Huang, Tao Tao, Ting Zhi, Yu Yan, Zili Xie, Junyong Zheng, Youdou Zheng, Rong Zhang
Summary: This study designed hybrid plasmonic nanolasers with metal pad structures, which achieved ultralow-threshold plasmonic multimode lasing. The findings also indicated that suitable plasmonic structural parameters can improve the performance of the laser.
ACS APPLIED NANO MATERIALS
(2022)
Article
Physics, Applied
Y. C. Chow, C. Lynsky, S. Nakamura, S. P. DenBaars, C. Weisbuch, J. S. Speck
Summary: Differential carrier lifetime measurements were conducted on c-plane InGaN/GaN LEDs of different QW indium compositions, showing that doped barriers can reduce the internal electric field and improve electron-hole wavefunction overlap. LEDs with higher indium composition demonstrate better performance despite the introduction of more non-radiative recombination centers.
APPLIED PHYSICS LETTERS
(2022)
Article
Materials Science, Multidisciplinary
C. K. Huang, C. Cheng, W. H. Lai, C. C. Chung, P. J. Chang, C. Y. Liu
Summary: An approach has been developed to measure the internal electrical field (Einternal) in InGaN quantum wells of GaN LEDs, with a linear relation established between forward voltage change and stressing voltage. By inducing a large reverse bias in the GaN LEDs, the initial compressive stress in MQWs was converted to a tensile state, reaching a stress-free condition at the transition point. The calculated Einternal across the In0.15Ga0.85N quantum wells was found to be in agreement with reported values.
MATERIALS CHEMISTRY AND PHYSICS
(2021)
Article
Engineering, Electrical & Electronic
Pradip Dalapati, Abdulaziz Almalki, Sultan Alhassan, Saud Alotaibi, Maryam Al Huwayz, Taiki Nakabayashi, Takashi Egawa, Makoto Miyoshi, Mohamed Henini
Summary: This study investigates the degradation mechanisms of InGaN/GaN multiple quantum well ultraviolet photodetectors (UV-PDs) by utilizing various optical and electrical measurements. The results indicate that the degradation of UV-PDs is primarily caused by newly generated defects.
SENSORS AND ACTUATORS A-PHYSICAL
(2022)
Article
Physics, Applied
Y. C. Chow, C. Lynsky, F. Wu, S. Nakamura, S. P. DenBaars, C. Weisbuch, J. S. Speck
Summary: This study investigates c-plane InGaN/GaN single quantum well light-emitting diodes of different well widths, showing that doped barriers can reduce the internal electric field in the quantum well, leading to improved electron-hole overlap and reduced efficiency droop. The addition of doped barriers enhances carrier confinement in excited states, resulting in higher efficiency and external quantum efficiency in the LEDs.
APPLIED PHYSICS LETTERS
(2021)
Article
Chemistry, Physical
Norhilmi Zahir, Noor Azrina Talik, Hazmi Naim Harun, Anas Kamarundzaman, Sarayut Tunmee, Hideki Nakajima, Narong Chanlek, Ahmad Shuhaimi, Wan Haliza Abd Majid
Summary: The properties of ITO films were found to be directly correlated with the substrate temperature during deposition. A substrate temperature of 450 degrees C was determined to produce the best ITO/p-GaN properties, exhibiting high power efficiency and the highest conduction band offset.
APPLIED SURFACE SCIENCE
(2021)
Article
Chemistry, Physical
Yutian Lin, Xin Chen, Jianqi Dong, Chenguang He, Wei Zhao, Zhitao Chen, Kang Zhang, Xingfu Wang
Summary: This study demonstrates the preparation of freestanding InGaN/GaN quantum-wells membrane and optimization of the emission intensity and polarization characteristics in vertical devices by introducing the Piezo-phototronic effect. Under external straining, the EL intensity of the LED is significantly increased, and the polarization ratio of emission light is adjusted. The polarization ratio of photoresponse current in PD also shows significant changes under different strain conditions.
Article
Physics, Applied
Nicola Roccato, Francesco Piva, Carlo De Santi, Riccardo Brescancin, Kalparupa Mukherjee, Matteo Buffolo, Camille Haller, Jean-Francois Carlin, Nicolas Grandjean, Marco Vallone, Alberto Tibaldi, Francesco Bertazzi, Michele Goano, Giovanni Verzellesi, Gaudenzio Meneghesso, Enrico Zanoni, Matteo Meneghini
Summary: This paper investigates and models the impact of defects on the electrical characteristics of InGaN-based LEDs as a function of the quantum well (QW) thickness. The study demonstrates that the density of defects scales with the increasing thickness of the InGaN QW, affecting the current-voltage characteristics significantly.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Physics, Applied
Sangeeta Singh, Pallavi Kumari
Summary: This study reports a novel n-type GaN/InGaN/GaN heterostructure vertical double-gate tunnel field-effect transistor (VTFET) using thorough calibrated simulation. By introducing a polarization layer near the source-channel junction, the drain current is increased due to the increase in charge concentration near the interface. The optimized structure with HfO2 as the dielectric material achieves excellent performance in terms of dc and analog/RF properties, making it a promising alternative for high-power steep switching analog and RF applications.
INTERNATIONAL JOURNAL OF MODERN PHYSICS B
(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
Physics, Applied
Mitsuru Funato, Yoshinobu Matsuda, Keito Mori-Tamamura, Atsushi A. Yamaguchi, Hiroki Goto, Yasunobu Sumida, Yujiro Ishihara, Yoichi Kawakami
Summary: InGaN/GaN quantum wells with atomically smooth surfaces and abrupt interfaces were homoepitaxially grown on GaN substrates. The optical anisotropy was examined using photo- and electroluminescence spectroscopies, which consistently showed in-plane optical polarization along the projection of the c-axis on the QW plane. The occurrence of polarization switching in strained, semipolar InGaN QWs was demonstrated and the experimental results were reasonably reproduced by a proposed analytical equation.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Boyang Lu, Zhibiao Hao, Yi Luo, Changzheng Sun, Yanjun Han, Bing Xiong, Jian Wang, Hongtao Li, Lai Wang
Summary: In this study, a simplified trap-assisted tunneling model is established to explain the experimental results by considering the energy distribution on trap states. The nonuniform distribution of diffused p-type dopants is identified as the cause of abnormal photocurrent experimental results.
JOURNAL OF APPLIED PHYSICS
(2022)
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
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
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)
