Article
Chemistry, Multidisciplinary
Hongyu Yang, Si Li, Lei Zhang, Wenbin Xiang, Yi Zhang, Xiaoyong Wang, Min Xiao, Yiping Cui, Jiayu Zhang
Summary: Semiconductor quantum dots have advantages in optoelectronic devices, but charged exciton states are unavoidable. This study synthesized CdSe/CdZnS/ZnS core/alloy shell/shell quantum dots with high photoluminescence quantum yield and systematically studied their multiexciton spectra and dynamics. The results showed that the band-edge biexciton is influenced by Coulomb interaction and Stark effect. A vertical microcavity surface-emitting laser device was fabricated using these quantum dots.
Article
Physics, Applied
Xuefeng Li, Nick Pant, Elizabeth DeJong, Abdelrahman Tarief Elshafiey, Rob Armitage, Emmanouil Kioupakis, Daniel Feezell
Summary: In this study, carrier dynamics in c-plane InGaN/GaN LEDs with various emission wavelengths near the green gap were investigated using a small-signal electroluminescence method. The causes of efficiency reduction at longer wavelengths were identified as a decrease in injection efficiency, radiative recombination rate, and an imbalance in Auger-Meitner and radiative terms due to the interplay between carrier-current density relationship and quantum-confined Stark effect. The effects of QCSE, phase-space filling, and carrier-current density relationship on efficiency reduction were examined separately using experimental data and Schrodinger-Poisson calculations.
APPLIED PHYSICS LETTERS
(2023)
Article
Optics
Hyun Jeong, Ga Hyun Cho, Mun Seok Jeong
Summary: We propose an efficient method to reduce efficiency droop in InGaN QWs by redistributing carrier localization through thermal annealing, resulting in increased internal quantum efficiency (IQE) in this study.
JOURNAL OF LUMINESCENCE
(2022)
Article
Optics
Konthoujam James Singh, Xiaotong Fan, Annada Sankar Sadhu, Chun-Ho Lin, Fang-Jyun Liou, Tingzhu Wu, Yu-Jung Lu, Jr-Hau He, Zhong Chen, Tom Wu, Hao-Chung Kuo
Summary: A flexible white-light system for high-speed visible-light communication (VLC) applications is proposed, consisting of a high-bandwidth CsPbBr3 quantum-dot paper and semipolar blue micro-LEDs, which could pave the way for VLC wearable devices.
PHOTONICS RESEARCH
(2021)
Article
Optics
Shukun Li, Guo Yu, Rui Lang, Menglai Lei, Huanqing Chen, Muhammad Saddique Akbar Khan, Linghai Meng, Hua Zong, Shengxiang Jiang, Peijun Wen, Wei Yang, Xiaodong Hu
Summary: In this study, a method was developed to describe the transport behaviors of electron and hole currents simultaneously in gallium nitride (GaN) light-emitting devices. Analytical models were established to explain the relationship between leakage current and total current in GaN-based laser diodes (LDs) and light-emitting diodes (LEDs), and these models were shown to accurately predict the sublinear behaviors of the luminescence-current curves of the devices.
Article
Crystallography
Yi-Tsung Chang, Mu-Jen Lai, Rui-Sen Liu, Shu-Chang Wang, Xiong Zhang, Lin-Jun Zhang, Yu-Hsien Lin, Shiang-Fu Huang, Lung-Chien Chen, Ray-Ming Lin
Summary: This study found that the current droop in AlGaN-based UVB light-emitting diodes is more noticeable at higher temperatures, despite both the main and parasitic peaks decreasing in intensity with increasing temperature. However, the slower temperature droop does not occur when the forward current is increased to temperatures above 298 K. After a 6000-hour aging period, the emission wavelengths do not show obvious changes, while the intensity of the parasitic peak remains nearly unchanged. Therefore, the degradation in light output power during long-term operation is not significantly correlated to the presence of the parasitic peak.
Article
Multidisciplinary Sciences
Hyungjin Kim, Shiekh Zia Uddin, Naoki Higashitarumizu, Eran Rabani, Ali Javey
Summary: The study found that by applying small mechanical strain, nonradiative exciton-exciton annihilation in transition metal dichalcogenide monolayers can be suppressed, allowing them to maintain a high photoluminescence quantum yield at high brightness levels.
Article
Optics
JingLin Zhan, ZhiZhong Chen, ChengCheng Li, YiYong Chen, JingXin Nie, ZuoJian Pan, ChuHan Deng, Xin Xi, Fei Jiao, XiangNing Kang, ShunFeng Li, Qi Wang, TongJun Yu, YuZhen Tong, GuoYi Zhang, Bo Shen
Summary: Micro-LEDs can operate at high injection levels, suitable for high-brightness micro-displays and visible light communication, but factors affecting device characteristics become more prominent as current density increases. Coulomb enhancement with polarization screening leads to an abnormal increase in external quantum efficiency at high current densities.
Article
Nanoscience & Nanotechnology
R. M. Barrett, J. M. McMahon, R. Ahumada-Lazo, J. A. Alanis, P. Parkinson, S. Schulz, M. J. Kappers, R. A. Oliver, D. Binks
Summary: The internal quantum efficiency of (In, Ga)N/GaN quantum wells can exceed 90% for blue-emitting structures, but decreases for longer wavelengths and higher excitation rates, known as efficiency droop, which limits the brightness of LEDs based on such quantum wells. Various mechanisms have been proposed to explain efficiency droop, but it is still unclear which one is the most important due to the difficulty in reconciling theoretical calculations with measurements.
Review
Optics
Jinchai Li, Na Gao, Duanjun Cai, Wei Lin, Kai Huang, Shuping Li, Junyong Kang
Summary: This paper reviews recent advances in ultraviolet LEDs and summarizes that multiple physical fields could build a toolkit for effectively controlling and tailoring crucial properties of nitride quantum structures.
LIGHT-SCIENCE & APPLICATIONS
(2021)
Article
Optics
Jeong-Hwan Park, Markus Pristovsek, Wentao Cai, Heajeong Cheong, Takeru Kumabe, Dong-Seon Lee, Tae-Yeon Seong, Hiroshi Amano
Summary: This Letter investigates the impact of shape on micro light-emitting diodes (μLEDs) and finds that the light extraction efficiency and internal quantum efficiency have different trends under different mesa shapes. By etching the sidewalls using tetramethylammonium hydroxide, the peak quantum efficiency of the LEDs can be increased and the sidewall dependency can be reduced.
Article
Polymer Science
Chai Won Kim, Ji Hye Lee, Seunguk Cho, Hyung Jong Kim, Jinhyo Hwang, Yong Woo Kim, Dae Hyuk Choi, Min Ju Cho, Kwangyeol Lee, Dong Hoon Choi
Summary: The novel hole transport polymer P-CzAc was synthesized for solution-processed green QD-LEDs, exhibiting good solubility and high hole mobility to reduce charge injection barriers and improve device efficiency.
Article
Materials Science, Multidisciplinary
Chuanyu Jia, Chenguang He, Zhiwen Liang, Qi Wang
Summary: The study reveals that utilizing In-component-graded InGaN barrier in InGaN light emitting diodes can enhance radiative recombination rate and decrease efficiency droop. The external quantum efficiencies and efficiency droop of LEDs vary with different designs of InGaN barrier, showing the importance of barrier design in LED performance.
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE
(2021)
Review
Engineering, Electrical & Electronic
Yukta, Soumitra Satapathi
Summary: Two-dimensional metal halide perovskites have revolutionized LED technology due to their tunable photophysical properties. However, challenges such as phase impurity and inefficient energy funneling still exist. Researchers have implemented various strategies to address these issues and enhance light emission from PeLEDs.
ACS APPLIED ELECTRONIC MATERIALS
(2022)
Article
Chemistry, Physical
Hanjun Yang, Jun Tang, Liangliang Deng, Zhe Liu, Xia Yang, Zengqi Huang, Haomiao Yu, Kai Wang, Jinpeng Li
Summary: Quasi-2D perovskites show promise for highly stable LEDs. Researchers inhibit defects in Dion-Jacobson-type perovskite LEDs through an excessive-salt-assisted process and antisolvent treatments. Building a bulk junction interface and enhancing surface polarization improve charge carrier injection and recombination in high-performance LED devices.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)
Article
Multidisciplinary Sciences
Jeng-Yuan Tsai, Jinbo Pan, Hsin Lin, Arun Bansil, Qimin Yan
Summary: The study identifies suitable defect centers in two-dimensional transition metal dichalcogenides and assesses their potential as solid-state spin qubits through high-throughput simulations. The authors show that these atomically thin materials offer a new platform for scalable qubit fabrication and operation at room temperature. The presence of neutral antisite defects in the transition metal dichalcogenides is found to enable controllable spin qubits with a paramagnetic triplet ground state.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Multidisciplinary
Simrjit Singh, Weiyi Gong, Christopher E. Stevens, Jin Hou, Aditya Singh, Huiqin Zhang, Surendra B. Anantharaman, Aditya D. Mohite, Joshua R. Hendrickson, Qimin Yan, Deep Jariwala
Summary: This article investigates the interlayer exciton phenomenon in two-dimensional heterostructures, and demonstrates the observation of helicity-resolved interlayer excitons through spin-valley layer coupling. This method does not require a specific geometric arrangement, such as twist angle or thermal annealing. The research shows that there are spin-valley-dependent optical selection rules in two-dimensional perovskites and monolayer transition metal dichalcogenides.
Article
Physics, Applied
Yuanpeng Wu, Ping Wang, Woncheol Lee, Anthony Aiello, Parag Deotare, Theodore Norris, Pallab Bhattacharya, Mackillo Kira, Emmanouil Kioupakis, Zetian Mi
Summary: Both 2D TMDs and III-V semiconductors are potential platforms for quantum technology, but each with its limitations. 2D TMDs have a large exciton binding energy and customizable quantum properties, but compatibility issues with existing industrial processes. On the other hand, III-nitrides have been widely used in light-emitting devices and power electronics but lack exploitation of excitonic quantum aspects. Recent advancements in 2D III-nitrides have shown promise in achieving room-temperature quantum technologies.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Woncheol Lee, Zhengyang Lyu, Zidong Li, Parag B. Deotare, Emmanouil Kioupakis
Summary: In this study, the influence of spin-orbit coupling on the electronic and optical properties of PbI2 was investigated using first-principles calculations. It was found that spin-orbit coupling not only altered the bandgap of PbI2 but also caused the mixing of orbital characters, resulting in changes in band structure and charge carrier effective masses. Additionally, spin-orbit coupling affected the optical transition matrix elements and absorption spectrum of PbI2. The experimental results supported the computational findings and highlighted the importance of spin-orbit coupling in the optical processes of PbI2.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Xuefeng Li, Nick Pant, Elizabeth DeJong, Abdelrahman Tarief Elshafiey, Rob Armitage, Emmanouil Kioupakis, Daniel Feezell
Summary: In this study, carrier dynamics in c-plane InGaN/GaN LEDs with various emission wavelengths near the green gap were investigated using a small-signal electroluminescence method. The causes of efficiency reduction at longer wavelengths were identified as a decrease in injection efficiency, radiative recombination rate, and an imbalance in Auger-Meitner and radiative terms due to the interplay between carrier-current density relationship and quantum-confined Stark effect. The effects of QCSE, phase-space filling, and carrier-current density relationship on efficiency reduction were examined separately using experimental data and Schrodinger-Poisson calculations.
APPLIED PHYSICS LETTERS
(2023)
Article
Multidisciplinary Sciences
Yulong Huang, Arjun K. Pathak, Jeng-Yuan Tsai, Clayton Rumsey, Mathew Ivill, Noah Kramer, Yong Hu, Martin Trebbin, Qimin Yan, Shenqiang Ren
Summary: This study reports on the pressure-controlled interlayer magnetic coupling of molecular layered compounds via chromium-pyrazine coordination. Room-temperature long-range magnetic ordering exhibits pressure tuning, with a strong dependence on alkali metal stoichiometry and composition.
NATURE COMMUNICATIONS
(2023)
Article
Physics, Applied
Su-Hyun Yoo, Mira Todorova, Jorg Neugebauer, Chris G. Van de Walle
Summary: GaN/(Al, Ga)N heterojunctions are crucial for high-electron-mobility transistors. The density of the two-dimensional electron gas (2DEG) on the GaN side is significantly enhanced by the strong polarization fields at the interface. The source of the electrons in the 2DEG is intrinsic to the overall structure and the negative charge is balanced by fixed charge on the surface, rather than surface states.
PHYSICAL REVIEW APPLIED
(2023)
Article
Nanoscience & Nanotechnology
David Arto Laleyan, Woncheol Lee, Ying Zhao, Yuanpeng Wu, Ping Wang, Jun Song, Emmanouil Kioupakis, Zetian Mi
Summary: Two-dimensional hexagonal boron nitride (h-BN) shows great promise for far ultraviolet (UV-C) light emission with higher quantum efficiency than other indirect bandgap materials, enabled by strong excitonic effects and efficient exciton-phonon interactions. This study offers a new approach for the design and development of far UV-C optoelectronic devices and quantum photonic devices using 2D semiconductor active regions.
Article
Quantum Science & Technology
Mehmet T. Uysal, Mouktik Raha, Songtao Chen, Christopher M. Phenicie, Salim Ourari, Mengen Wang, Chris G. Van de Walle, Viatcheslav V. Dobrovitski, Jeff D. Thompson
Summary: In this work, coherent coupling between the electron spin of a single Er3+ ion and a single I = 1/2 nuclear spin in the solid-state host crystal, which is a fortuitously located proton (1H), is demonstrated. The nuclear spin is controlled using dynamical-decoupling sequences applied to the electron spin, allowing for one- and two-qubit gate operations. The longer coherence time of the nuclear spin, compared to the electron spin, is crucial for combining long-lived nuclear spin quantum registers with telecom-wavelength emitters for long-distance quantum repeaters.
Article
Physics, Multidisciplinary
Fangzhou Zhao, Mark E. Turiansky, Audrius Alkauskas, Chris G. Van de Walle
Summary: Trap-assisted Auger-Meitner recombination is highlighted as a dominant nonradiative process in wide-band-gap materials, and a first-principles methodology is presented to determine the rates of this process in semiconductors or insulators due to defects or impurities.
PHYSICAL REVIEW LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Xiao Zhang, Emmanouil Kioupakis
Summary: Silicon carbide (SiC) is widely used in electronic and optoelectronic applications as an indirect-gap semiconductor material. The computational cost has hindered theoretical investigations of phonon-assisted absorption, despite the existence of experimental measurements for more than 50 years. In this study, we calculate the temperature-dependent optical absorption spectra of common SiC polytypes using first-principles approaches. Our results agree with experimental absorption coefficients and predict the temperature dependence by considering the band gap. Considering the electronic energy renormalization due to temperature is important for improving the prediction of phonon-assisted absorption in SiC. Our insights can be applied to predict the optical spectra of other indirect-gap semiconductors and less common SiC polytypes in general.
Article
Materials Science, Multidisciplinary
Ymir K. Frodason, Joel B. Varley, Klaus Magnus H. Johansen, Lasse Vines, Chris G. Van de Walle
Summary: Pathways and energy barriers for the migration of Ga vacancies (VGa) and Ga interstitials (Gai) in-Ga2O3 have been studied using hybrid functional calculations and the nudged elastic band method. A mechanism for the transformation of VGa between different split configurations has been described. The overall migration barriers for VGa and Gai in different crystal directions have been determined. The results provide insights into the thermally activated recovery processes in irradiated material.
Article
Materials Science, Multidisciplinary
Xiao Zhang, Guangsha Shi, Joshua A. Leveillee, Feliciano Giustino, Emmanouil Kioupakis
Summary: This paper introduces the issue of light absorption by free carriers in semiconductors resulting in optical loss. It develops a theoretical model taking into account both single-particle excitations and the collective Drude term, and applies it to the case of doped Si. The model demonstrates excellent agreement with experimental data and analyzes the dominant processes contributing to free-carrier absorption at different photon wavelengths.
Article
Materials Science, Multidisciplinary
Yubi Chen, Mark E. Turiansky, Chris G. Van de Walle
Summary: This study conducted comprehensive investigations on native point defects in beryllium oxide (BeO) using density functional theory. The stability and potential applications of different defects were analyzed, and suitable candidates for quantum defects were identified.
Article
Quantum Science & Technology
Raj N. Patel, David A. Hopper, Jordan A. Gusdorff, Mark E. Turiansky, Tzu-Yung Huang, Rebecca E. K. Fishman, Benjamin Porat, Chris G. Van de Walle, Lee C. Bassett
Summary: By using photon emission correlation spectroscopy, we revealed the optical dynamics of quantum emitters in hexagonal boron nitride. The experimental results showed the existence of quantum emitters with ideal single-photon emission and their photoluminescence emission lineshapes were consistent with individual vibronic transitions. However, polarization-resolved excitation and emission revealed the role of multiple optical transitions, and photon emission correlation spectroscopy revealed the complicated optical dynamics associated with excitation and relaxation.
