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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Excitation and amplification of the unidirectionally propagating terahertz plasmon in a periodical graphene structure
摘要： The amplification of unidirectionally propagating plasmon modes excited by the incident terahertz wave in a periodical structure with an active graphene is studied theoretically. The amplification of propagating plasmon modes is due to radiative recombination in inverted graphene.
关键词： plasmon,radiative recombination,amplification,terahertz,graphene
更新于2025-09-16 10:30:52
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Model for electroluminescence in single-walled carbon nanotube field effect transistor under transverse magnetic field
摘要： Electroluminescence spectrum and radiative recombination rate of short channel single-walled carbon nanotube field effect transistor in presence of transverse magnetic field is calculated by using non-equilibrium Green’s function method. Significant enhancement in radiative recombination rate and red shift in electroluminescence spectrum are observed with increase in the strength of magnetic field. The band gap suppression estimated from energy position resolved local density of states calculation plays a dominant role in transport mechanism under the influence of external magnetic field. The tuning of electroluminescence spectrum of single-walled carbon nanotube by transverse magnetic field can be employed as nanoscale optical source in next generation optoelectronic and photonic devices.
关键词： electroluminescence,single-walled carbon nanotube,optoelectronics,radiative recombination rate,plasmonics,field effect transistor
更新于2025-09-16 10:30:52
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Investigation on voltage loss in organic triplet photovoltaic devices based on Ir complexes
摘要： Voltage losses in singlet material-based organic photovoltaic devices (OPVs) have been intensively studied, whereas, only a few investigations on triplet material-based OPVs (T-OPVs) are reported. To investigate the voltage loss in T-OPVs, two homoleptic iridium(III) complexes based on extended p-conjugated benzo[g]phthalazine ligands, Ir(Ftbpa)3 and Ir(FOtbpa)3, are synthesized as sole electron donors. T-OPVs are fabricated by mixing two donors with phenyl-C71-butyric acid methyl ester (PC71BM) as an electron acceptor. Insertion of oxygen-bridges as flexible inert d-spacers in Ir(FOtbpa)3 has slightly elevated both the lowest unoccupied molecular orbital and the highest occupied molecular orbital levels compared to those of Ir(Ftbpa)3, which results in a lower charge transfer (CT) state energy (ECT) for Ir(FOtbpa)3-based devices. However, a higher Voc (0.88 V) is observed for Ir(FOtbpa)3-based devices than those of Ir(Ftbpa)3 (0.80 V). To understand the above result, the morphologies of the two blend films are studied, which excludes the influence of morphology. Furthermore, radiative and non-radiative recombination in two devices is quantitatively investigated, which suggests that a higher Voc can be attributed to reduced radiative and non-radiative recombination loss for the Ir(FOtbpa)3-based devices.
关键词： charge transfer state energy,organic photovoltaic devices,triplet material-based OPVs,radiative and non-radiative recombination,iridium(III) complexes,voltage loss
更新于2025-09-12 10:27:22
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Efficient sky-blue perovskite light-emitting diodes via photoluminescence enhancement
摘要： The efficiencies of green and red perovskite light-emitting diodes (PeLEDs) have been increased close to their theoretical upper limit, while the efficiency of blue PeLEDs is lagging far behind. Here we report enhancing the efficiency of sky-blue PeLEDs by overcoming a major hurdle of low photoluminescence quantum efficiency in wide-bandgap perovskites. Blending phenylethylammonium chloride into cesium lead halide perovskites yields a mixture of two-dimensional and three-dimensional perovskites, which enhances photoluminescence quantum efficiency from 1.1% to 19.8%. Adding yttrium (III) chloride into the mixture further enhances photoluminescence quantum efficiency to 49.7%. Yttrium is found to incorporate into the three-dimensional perovskite grain, while it is still rich at grain boundaries and surfaces. The yttrium on grain surface increases the bandgap of grain shell, which confines the charge carriers inside grains for efficient radiative recombination. Record efficiencies of 11.0% and 4.8% were obtained in sky-blue and blue PeLEDs, respectively.
关键词： radiative recombination,perovskite light-emitting diodes,yttrium (III) chloride,photoluminescence quantum efficiency,wide-bandgap perovskites
更新于2025-09-12 10:27:22
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Voltage dependent photoluminescence and how it correlates to the fill factor and open-circuit voltage in perovskite solar cells
摘要： Optimizing the photoluminescence (PL) yield of a solar cell has long been recognized as a key principle to maximize the power conversion efficiency. While PL measurements are routinely applied to perovskite films and solar cells under open-circuit conditions (VOC), it remains unclear how the emission depends on the applied voltage. Here, we performed PL(V) measurements on perovskite cells with different hole transport layer thicknesses and doping concentrations resulting in remarkably different fill factors (FFs). The results reveal that PL(V) mirrors the current-voltage (JV) characteristics in the power-generating regime, which highlights an interesting correlation between radiative and non-radiative recombination losses. In particular, high FF devices show a rapid quenching of PL(V) from open-circuit to the maximum power point. We conclude that while the PL has to be maximized at VOC, at lower biases <VOC, the PL must be rapidly quenched as charges need to be extracted prior to recombination.
关键词： perovskite solar cells,radiative recombination,photoluminescence,open-circuit voltage,fill factor,non-radiative recombination
更新于2025-09-11 14:15:04
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Role of the relative phase and intensity ratio in electron-ion recombination assisted by a bicircular laser field
摘要： S-matrix theory is used in order to analyze the energy spectra of electron-ion radiative recombination assisted by a bicircular (two-component circularly polarized) laser field. The analysis includes the cases of corotating and counterrotating laser-field components. The scattering effects are also included by applying the second Born approximation in the expansion of the S-matrix element. We have investigated the sensitivity of the emitted photon energy spectra to the relative phase and intensity ratio of the laser-field components. The obtained energy spectra show the plateau-like oscillatory structures with abrupt cutoffs. Positions of these cutoffs in the energy spectra are confirmed by a classical analysis. Scattering effects may be observed in the calculated energy spectra not only in the case of counterrotating, but also in the case of corotating laser-field components. This is different from the process of above-threshold ionization/detachment by a bicircular laser field, where the scattering effects in the photoelectron energy spectra may be observed only in the case of counterrotating laser-field components.
关键词： scattering effects,intensity ratio,electron-ion radiative recombination,bicircular laser field,relative phase,S-matrix theory
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE 2nd International Conference on Electronics Technology (ICET) - Chengdu, China (2019.5.10-2019.5.13)] 2019 IEEE 2nd International Conference on Electronics Technology (ICET) - Increased Radiative Recombination in Nitride Laser Diodes with Inverse Tapered Electron Blocking Layer
摘要： A deep ultraviolet laser structure was proposed, which can lase at 261 nm band. In this simulation, the width of this laser diode was set to 4 μm and the cavity length was set to 530 μm. The mirror reflective index and the background loss were set to 0.05 and 2400, respectively. All the characteristics of the deep-UV laser diode were simulated under room temperature. The tapered EBL (electron bl1ocking layer), the inverse tapered EBL and the reference EBL were applied to this laser. When the tapered EBL is replaced by the inverse tapered EBL, the effective potential height of the EBL increased from 532 meV to 610 meV. This improvement means higher electronic blocking ability. More electrons will be confined to the active layer. Compared with the reference EBL, the electron leakage of inverse reduced about 22.7%. The concentration of carriers in the active layer is simulated. The radiative concentration increased by 1.48% for the inverse tapered EBL. The promotion of the radiative concentration indicated higher laser’s output power. The inverse tapered EBL is a far-reaching structure for laser diodes.
关键词： electron leakage,radiative recombination,laser diodes,the inverse tapered EBL
更新于2025-09-11 14:15:04
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Minimizing non-radiative recombination losses in perovskite solar cells
摘要： Photovoltaic solar cells based on metal-halide perovskites have gained considerable attention over the past decade because of their potentially low production cost, earth-abundant raw materials, ease of fabrication and ever-increasing power-conversion efficiencies of up to 25.2%. This type of solar cells offers the promise of generating electricity at a more competitive unit price than traditional fossil fuels by 2035. Nevertheless, the best research-cell efficiencies are still below the theoretical limit defined by the Shockley–Queisser theory, owing to the presence of non-radiative recombination losses. In this Review, we analyse the predominant pathways that contribute to non-radiative recombination losses in perovskite solar cells and evaluate their impact on device performance. We then discuss how non-radiative recombination losses can be estimated through reliable characterization techniques and highlight some notable advances in mitigating these losses, which hint at pathways towards defect-free perovskite solar cells. Finally, we outline directions for future work that will push the efficiency of perovskite solar cells towards the radiative limit.
关键词： defect passivation,photovoltaic,perovskite solar cells,Shockley–Queisser theory,non-radiative recombination losses
更新于2025-09-11 14:15:04
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Metamorphic InAs(Sb)/InGaAs/InAlAs nanoheterostructures grown on GaAs for efficient mid-IR emitters
摘要： High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5 μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1 ? are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ～8 μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic InxAl1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded InxAl1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6 μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T = 10–300 K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As4/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3 × 107 cm?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300 nm, the extremely low surface roughness with the RMS value of 1.6–2.4 nm, measured by AFM, as well as rather high 3.5 μm-PL intensity at temperatures up to 300 K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.
关键词： Buffer layer,Non-radiative recombination,Mid-infrared emitters,Photoluminescence,Metamorphic heterostructures,InSb,InAs,Structural properties,Molecular beam epitaxy,Nanostructures,In(Ga,Al)As ternary alloys,Threading dislocations,Quantum well
更新于2025-09-04 15:30:14