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Strain-tunable entangled-light-emitting diodes with high yield and fast operation speed  [PDF]
Jiaxiang Zhang,Johannes S. Wildmann,Fei Ding,Rinaldo Trotta,Yongheng Huo,Eugenio Zallo,Daniel Huber,Armando Rastelli,Oliver G. Schmidt
Physics , 2015,
Abstract: Triggered sources of entangled photons play crucial roles in almost any existing protocol of quantum information science. The possibility to generate these non-classical states of light with high speed and using electrical pulses could revolutionize the field. Entangled-light-emitting-diodes (ELEDs) based on semiconductor quantum dots (QDs) are at present the only devices that can address this task 5. However, ELEDs are plagued by a source of randomness that hampers their practical exploitation in the foreseen applications: the very low probability (~10-2) of finding QDs with sufficiently small fine-structure-splitting for entangled-photon-generation. Here, we overcome this hurdle by introducing the first strain-tunable ELEDs (S-ELEDs) that exploit piezoelectric-induced strains to tune QDs for entangled-photon-generation. We demonstrate that up to 30% of the QDs in S-ELEDs emit polarization-entangled photon pairs with entanglement-fidelities as high as f+ = 0.83(5). Driven at the highest operation speed of 400 MHz ever reported so far, S-ELEDs emerge as unique devices for high-data rate entangled-photon applications.
Electrically Tunable Excitonic Light Emitting Diodes based on Monolayer WSe2 p-n Junctions  [PDF]
Jason S. Ross,Philip Klement,Aaron M. Jones,Nirmal J. Ghimire,Jiaqiang Yan,D. G. Mandrus,Takashi Taniguchi,Kenji Watanabe,Kenji Kitamura,Wang Yao,David H Cobden,Xiaodong Xu
Physics , 2013, DOI: 10.1038/nnano.2014.26
Abstract: Light-emitting diodes are of importance for lighting, displays, optical interconnects, logic and sensors. Hence the development of new systems that allow improvements in their efficiency, spectral properties, compactness and integrability could have significant ramifications. Monolayer transition metal dichalcogenides have recently emerged as interesting candidates for optoelectronic applications due to their unique optical properties. Electroluminescence has already been observed from monolayer MoS2 devices. However, the electroluminescence efficiency was low and the linewidth broad due both to the poor optical quality of MoS2 and to ineffective contacts. Here, we report electroluminescence from lateral p-n junctions in monolayer WSe2 induced electrostatically using a thin boron nitride support as a dielectric layer with multiple metal gates beneath. This structure allows effective injection of electrons and holes, and combined with the high optical quality of WSe2 it yields bright electroluminescence with 1000 times smaller injection current and 10 times smaller linewidth than in MoS2. Furthermore, by increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged, and neutral excitons. This system has the required ingredients for new kinds of optoelectronic devices such as spin- and valley-polarized light-emitting diodes, on-chip lasers, and two-dimensional electro-optic modulators.
The Investigation on Color Purity of Blue Organic Light-Emitting Diodes (BOLED) by Hole-Blocking Layer  [PDF]
Kan-Lin Chen,Chien-Jung Huang,Wen-Ray Chen,Chih-Chieh Kang,Wen-How Lan,Yu-Chen Lee
International Journal of Photoenergy , 2013, DOI: 10.1155/2013/878537
Abstract: Organic light-emitting diodes (OLEDs) with triple hole-blocking layer (THBL) structure, which consist of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,4′-bis(2,2′diphenyl vinil)-1,1′-biphenyl (DPVBi), and (4,4′-N,N′-dicarbazole)biphenyl (CBP), have been fabricated. Regardless of applied voltage variation, the luminous efficiency of the OLEDs with THBL structure was increased by 41% as compared with the dual hole-blocking layer (DHBL) structure. The CIE coordinates of (0.157, 0.111) of device with THBL structure are close to pure blue emission than that of other devices of DHBL. There is a coordinate with the slight shift of = (0.001, 0.008) for the device with THBL structure during the applied voltage of 6–9?V. The results indicate that the excitons can be effectively confined in the emitting layer of device, leading to an enhancement of luminance efficiency and more stable coordinate. 1. Introduction Recently, organic light-emitting diodes (OLEDs) have attracted much attention due to their superior characteristics such as high luminance, wide range of colors, and wide viewing angles. OLEDs have been regarded as the next generation display technology. Many approaches have been tried to realize full-color displays [1], and it requires three basic emitting colors, red, green, and blue. However, the blue OLEDs still have inherent problems of low efficiency, poor color purity, and short lifetime in comparison with other red or green OLEDs [2]. It is important to keep the color stability with applied voltage in the blue OLEDs. So far, there is still a distance to achieve standard Commission International de L’Eclairage (CIE) coordinates (0.14, 0.08) of blue OLEDs. Generally, there are many structures of emitting layer to obtain blue OLEDs, such as single emitting layer, double emitting layer, blue guest doped layer, or multiple-quantum-well (MQW) layer [3–12]. Shi et al. utilized MQW structure of [4,4-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) that makes hole-electron balance in emitting layer, resulting in the CIE coordinates of (0.1747, 0.1059) [11]. Bang et al. used 4,4′-bis(2,2′diphenyl vinil)-1,1′-biphenyl (DPVBi) and tris-8-hydroxy-quinoline aluminum (Alq3) as double emitting layer, leading to CIE coordinates of (0.150, 0.137) at 11?V [2]. However, the CIE coordinates are not stable by using the above structure or method, resulting from the shift of the excitons recombination zone. In this study, we improved the color purity of OLEDs by using structure of triple-hole blocking layer
Light Emitting Diodes of Inverse Spin Valves
X. R. Wang
Physics Research International , 2008, DOI: 10.1155/2008/434936
Abstract: Light emitting diodes made out of inverse spin valves of a ferromagnetic half metal sandwiched between two nonmagnetic metals are proposed. Based on a giant spin-dependent chemical potential difference created under an external bias, the inverse spin valves are possible to emit light when electrons with the higher chemical potential flip their spins and become the electrons of the opposite spin with the lower chemical potential. The frequency of this type of light emitting diodes is tunable by the bias.
Increased color conversion efficiency in hybrid light emitting diodes utilizing non-radiative energy transfer  [PDF]
S. Chanyawadee,P. G. Lagoudakis,R. T. Harley,M. D. B. Charlton,D. V. Talapin,S. Lin
Physics , 2009,
Abstract: We fabricate a highly efficient colour conversion light emitting diode consisting of surface-patterned blue emitters and semiconductor colloidal nanocrystal quantum dots (NQDs). Electrically injected carriers in the blue emitter (donor) are efficiently transferred to the NQDs (acceptor) via nonradiative energy transfer in addition to conventional radiative energy transfer. The existence of nonradiative energy transfer is verified by the simultaneous observation of increased donor emission decay rate, the transient transfer of carriers at the acceptor and a 2-fold enhancement of the NQD electroluminescence.
Powerful infrared emitting diodes
Kogan L. M.
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature , 2012,
Abstract: Powerful infrared LEDs with emission wavelength 805 ± 10, 870 ± 20 and 940 ± 10 nm developed at SPC OED "OPTEL" are presented in the article. The radiant intensity of beam diode is under 4 W/sr in the continuous mode and under 100 W/sr in the pulse mode. The radiation power of wide-angle LEDs reaches 1 W in continuous mode. The external quantum efficiency of emission IR diodes runs up to 30%. There also has been created infrared diode modules with a block of flat Fresnel lenses with radiant intensity under 70 W/sr.
Optoelectronics with electrically tunable PN diodes in a monolayer dichalcogenide  [PDF]
Britton W. H. Baugher,Hugh O. H. Churchill,Yafang Yang,Pablo Jarillo-Herrero
Physics , 2013, DOI: 10.1038/nnano.2014.25
Abstract: One of the most fundamental devices for electronics and optoelectronics is the PN junction, which provides the functional element of diodes, bipolar transistors, photodetectors, LEDs, and solar cells, among many other devices. In conventional PN junctions, the adjacent p- and n-type regions of a semiconductor are formed by chemical doping. Materials with ambipolar conductance, however, allow for PN junctions to be configured and modified by electrostatic gating. This electrical control enables a single device to have multiple functionalities. Here we report ambipolar monolayer WSe2 devices in which two local gates are used to define a PN junction exclusively within the sheet of WSe2. With these electrically tunable PN junctions, we demonstrate both PN and NP diodes with ideality factors better than 2. Under excitation with light, the diodes show photodetection responsivity of 210 mA/W and photovoltaic power generation with a peak external quantum efficiency of 0.2%, promising numbers for a nearly transparent monolayer sheet in a lateral device geometry. Finally, we demonstrate a light-emitting diode based on monolayer WSe2. These devices provide a fundamental building block for ubiquitous, ultra-thin, flexible, and nearly transparent optoelectronic and electronic applications based on ambipolar dichalcogenide materials.
Contact Injection into Polymer Light-Emitting Diodes  [PDF]
E. M. Conwell,M. W. Wu
Physics , 1997, DOI: 10.1063/1.118716
Abstract: The variation of current I with voltage V for poly(phenylene vinylene) and other polymer light-emitting diodes has been attributed to carriers tunneling into broad conduction and valence bands. In actuality the electrons and holes tunnel into polaron levels and transport is by hopping among these levels. We show that for small injection the I-V characteristic is determined mainly by the image force, for large injection by space charge effects, but in both cases the strong variation of mobility with field due to disorder plays an important role.
Near infrared polymer light-emitting diodes
Zhang Yong,Yang Jian,Hou Qiong,Mo Yueqi,Peng Junbiao,Cao Yong
Chinese Science Bulletin , 2005, DOI: 10.1360/04wb0128
Abstract: High efficiency of near infrared polymer light-emitting diodes with bilayer structure was obtained. The diode structure is ITO/PEDOT/L1/L2/Ba/Al, where L1 is phenyl-substituted poly [p-phenylphenylene vinylene] derivative (P-PPV), L2 is 9,9-dioctylfluorene (DOF) and 4,7-bis (3-hexylthiophen)-2-yl-2,l,3-naphthothiadiazole (HDNT) copolymer (PFHDNT10). The electroluminescence (EL) spectrum of diodes from PFHDNT10 is at 750 nm located in the range of near infrared. The maximum external quantum efficiency is up to 2.1% at the current density of 35 mA/cm2. The improvement of the diode’s performances was considered to be the irradiative excitons confined in the interface between L1 and L2 layers.
Near infrared polymer light-emitting diodes
Zhang Yong,Yang Jian,Hou Qiong,Mo Yueqi,Peng Junbiao,Cao Yong,
ZHANGYong
,YANGJian,HOUQiong,MOYueqi,PENGJunbiao,CAOYong

科学通报(英文版) , 2005,
Abstract: High efficiency of near infrared polymer light-emitting diodes with bilayer structure was obtained. The diode structure is ITO/PEDOT/L1/L2/Ba/Al, where L1 is phenyl-substituted poly p-phenylphenylene vinylene] derivative (P-PPV), L2 is 9,9-dioctylfluorene (DOF) and 4,7-bis (3-hexylthiophen)-2-yl-2,l,3-naphthothiadiazole (HDNT) copolymer (PFHDNT10). The electroluminescence (EL) spectrum of diodes from PFHDNT10 is at 750 nm located in the range of near infrared. The maximum external quantum efficiency is up to 2.1% at the current density of 35 mA/cm2. The improvement of the diode’s performances was considered to be the irradiative excitons confined in the interface between L1 and L2 layers.
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