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Ultraefficient Green LEDs Using Quantum Dots in Liquid Matrix
摘要： Green spectral range, which has the highest human eye sensitivity, is one of the most fundamental colors in lighting and display. Quantum dots (QDs) offer exceptional optical properties including high quantum yield (QY), strong absorption, and narrow emission linewidths for efficient green-emitting diodes. In this article, we demonstrated QD-based light-emitting diodes (QD-LEDs) that operate at a luminous efficiency (LE) level of 95 lumens per electrical watt, the luminous efficacy of optical radiation of 409 lumens per optical watt, and external quantum efficiency (EQE) of 23.3% in the green spectral region. For that, we synthesized 1-octanethiol-capped CdSe/ZnS QDs with an absolute QY of 91% and integrated them in a liquid matrix that allows conservation of the QD efficiency in device architecture. Our simulations were in agreement with the performance of the fabricated QD-LEDs, and they showed that the QD-LEDs can be further improved to reach LE levels over 250 lm/W.
关键词： light-emitting diodes (LEDs),luminous efficiency (LE),liquid-state integration,quantum dots (QDs),External quantum efficiency (EQE)
更新于2025-09-12 10:27:22
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Interplay between various active regions and the interband transition for AlGaN-based deep-ultraviolet light-emitting diodes to enable a reduced TM-polarized emission
摘要： Al-rich AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) have a low light extraction efficiency, especially when the emission wavelength is shorter than 280 nm, and this is partially because of the dominant transverse-magnetic polarized light. Our results show that the transverse-electric (TE) polarized light can be obtained even if the emission wavelength becomes even shorter by reducing the quantum well thickness. The ultrathin quantum well enables the enhanced TE-polarized emission that arises from the redistributed subbands for holes. On the contrary to the common belief, we observe a blueshift for the emission wavelength when the AlN composition in the quantum barrier increases. The internal quantum efficiency (IQE) for DUV LEDs with ultrathin quantum wells is no longer determined by the quantum-confined Stark effect, while quantum barrier with high AlN composition is vitally important to improve the electron injection efficiency and thus enhance the IQE.
关键词： quantum well,AlGaN,quantum barrier,internal quantum efficiency,deep-ultraviolet,TE-polarized emission,light-emitting diodes
更新于2025-09-12 10:27:22
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Performance evaluation of composition graded layer of aSi1-xGex: H in n+aSi:H/i-aSi:H/p+aSi1-xGex:H graded band gap single junction solar cells
摘要： The work investigates the role of composition grading of amorphous silicon germanium alloy on single junction graded band gap amorphous silicon solar cells, for the first time. The fabrication and optical characterization of composition graded aSi1-xGex: H alloy by varying the gas flow rate of germane (GeH4) are presented. We propose the composition graded p+aSi1-xGex: H layer to be considered as one of the active layers in amorphous silicon based solar cells. The principle of operation of the solar cell is illustrated with the energy band diagram of proposed n+aSi:H/i-aSi:H/p+aSi1-xGex:H solar cell structure. Further, the behavior of the structure is evaluated through simulation in terms of proposed layer thickness variation and temperature variation. It is observed that the proposed structure is capable of delivering an open circuit voltage (V oc), short circuit current density (Jsc), Fill Factor (FF) and conversion efficiency (g) of 1.1 V, 15.56 mA/cm2, 0.885 and 15.19% respectively, which is at par with any other single junction amorphous silicon solar cells. The cell performance parameters were compared with related state of the art as well as our previous works. The performance parameters of proposed structure show that it is better to use a single composition graded layer instead of using a number of non-graded composition layers in photovoltaic structures, which reduces complexity and cost of fabrication.
关键词： Internal Quantum Efficiency,Optical band gap,Germane flow rate,Conversion efficiency,Composition grading,PECVD
更新于2025-09-12 10:27:22
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Photodetectors [Working Title] || Overcoming the Bandwidth-Quantum Efficiency Trade-Off in Conventional Photodetectors
摘要： Optical systems and microwave photonics applications rely heavily on high-performance photodetectors having a high bandwidth-efficiency product. The main types of photodetector structures include Schottky and PIN-photodiodes, heterojunction phototransistors, avalanche photodetectors, and metal-semiconductor-metal photodetectors. Vertically-illuminated photodetectors intrinsically present bandwidth-efficiency limitations, but these have been mitigated by new innovations over the years in quantum well photodetectors, edge-coupled photodetectors and resonant-cavity enhanced photodetectors for improved photophysical characteristics. Edge-coupled ultra-high-speed photodetectors have yielded high conversion efficiencies, and the active device structure of resonant-cavity-enhanced photodetectors allows wavelength selectivity and optical field enhancement due to resonance, enabling photodetectors to be made thinner and hence faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. Single-photon avalanche diodes have been developed, which combine an ultimate sensitivity with excellent timing accuracy. Further advances in addressing the bandwidth-quantum efficiency trade-off have incorporated photon-trapping nanostructures and plasmonic nanoparticles. Nanowire photodetectors have also demonstrated the highest photophysical performance to date.
关键词： photosensitivity,saturation current,quantum efficiency,optical absorption,drift layers,bandwidth-efficiency product
更新于2025-09-12 10:27:22
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Two-dimensional analysis of the nonuniform quantum yields of multiple quantum wells for AlGaN-based deep-ultraviolet LEDs grown on AlN templates with dense macrosteps using cathodoluminescence spectroscopy
摘要： AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) incorporating uneven multiple quantum wells (MQWs) with inclined and terrace zones, which were fabricated on an AlN template with dense macrosteps, have exhibited a high internal quantum efficiency (IQE). To investigate the microscopic structure of uneven MQWs, cathodoluminescence (CL) mapping characterization was carried out, and the maps of the CL intensity at 300 K relative to that at 38 K were obtained for uneven MQWs that targeted 265 and 285 nm LEDs. At an electron beam current of less than 1.0 nA, the signals from inclined and terrace zones of the uneven MQWs were confirmed to satisfy the non-saturated excitation condition at 300 K. Nonradiative recombination (NR) was insufficiently frozen even at 38 K, specifically on the terraces in the 265 nm MQW, suggesting high concentrations of NR centers due to point defects (PDs). In contrast, NR in the 285 nm MQW at 38 K was closer to freeze-out. The concentration of PDs in the 285 nm MQW was likely to be lower than that in the 265 nm MQW. Finally, the ratios of the CL intensity at 300 K to those at 38 K were mapped, demonstrating an approach to creating an approximate map of IQE. The values in the CL intensity ratio maps are discussed by considering the analytical error factors. The results support the model of localized current injection through Ga-rich stripe zones in the n-AlGaN cladding layer.
关键词： AlGaN,cathodoluminescence spectroscopy,internal quantum efficiency,deep-ultraviolet LEDs,multiple quantum wells
更新于2025-09-12 10:27:22
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Exploring Orbit–Orbit Interaction in Relationship to Photoluminescence Quantum Efficiency in Perovskite Quantum Dots through Rashba Effect
摘要： This study demonstrates the influence of orbit-orbit interaction on photoluminescence quantum efficiency (PLQE) of metal halide perovskite quantum dots (QDs) through Rashba effect. The orbit-orbit interaction between excitons was characterized by using the minimal excitation intensity required to generate photoluminescence difference (?PL) between linearly and circularly polarized photoexcitations. It was observed that changing the surface functionalization from PFOA-OA to PFSH-OAm and OA can largely increase the minimal excitation intensity for generating ?PL. This indicates that orbit-orbit interaction is essentially decreased in CsPbBr1I2 QDs with surface functionalization. Simultaneously, the PLQE is increased from 39 % to 59 % and 72 % in CsPbBr1I2 QDs upon surface functionalization. Furthermore, the PL lifetime is decreased with increasing the PLQE in CsPbBr1I2 QDs upon surface functionalization. This phenomenon implies that decreasing the orbit-orbit interaction can essentially weaken Rashba effect and consequently reduces the disallowed transitions, leading to an enhancement on PLQE in perovskite QDs.
关键词： Rashba effect,orbit-orbit interaction,Perovskite quantum dots,photoluminescence quantum efficiency
更新于2025-09-12 10:27:22
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Internal quantum efficiencies of AlGaN quantum dots grown by molecular beam epitaxy and emitting in the UVA to UVC ranges
摘要： AlyGa1?yN quantum dots (QDs) have been grown by molecular beam epitaxy on AlxGa1?xN (0001) using a 2-dimensional–3-dimensional growth mode transition that leads to the formation of QDs. QDs have been grown for Al compositions y varying between 10% and 40%. The influence of the active region design [composition y, QD height, and bandgap difference (ΔEg) between the AlxGa1?xN cladding layer and the AlyGa1?yN QDs] is discussed based on microscopy, continuous wave photoluminescence (PL), and time-resolved PL (TRPL) measurements. In particular, increasing y leads to a shift of the QD emission toward shorter wavelengths, allowing covering a spectral range in the UV from 332 nm (UVA) to 276 nm (UVC) at room temperature (RT). The low-temperature (LT) internal quantum efficiency of the QD ensembles was estimated from TRPL experiments at 8 K and values between 11% and 66% were deduced. The highest internal quantum efficiency (IQE)-LT is found for the QDs with higher Al content y. Then, the PL spectrally integrated intensity ratios between RT and LT were measured to estimate the IQE of the samples at RT. The PL ratio is higher for larger ΔEg, for QDs with y of 0.1 or 0.2, and high PL intensity ratios up to 30% were also measured for QDs with larger y of 0.3 and 0.4. RT IQE values between 5% and 20% are deduced for AlyGa1?yN QDs emitting in the 276–308 nm range.
关键词： AlGaN,internal quantum efficiency,UVC,quantum dots,molecular beam epitaxy,time-resolved photoluminescence,photoluminescence,UVA
更新于2025-09-12 10:27:22
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Optical Fiber Communications (Principles and Applications) || Optical Receivers
摘要： The purpose of a receiver in an electronic communication system is to extract the information sent by the corresponding transmitter with as minimum a carrier power level as possible. The primary function of an optical receiver in an optical fiber communication link is to convert the received optical signal into an equivalent electrical signal and recover the data. One of the main components of an optical receiver is a photodetector that converts incident optical signals into electric signals using photoelectric effects. High Sensitivity, dynamic range, fast response (i.e., acquisition time), high reliability, low noise, compatible size with that of fiber, and low cost are some of the important requirements of a photodetector. These requirements are best met by semiconductor photodetectors that convert an optical signal transmitted via optical fiber cables to equivalent electrical signals for further processing to achieve the desired output. The type of photodetectors suitable for three optical spectrum ranges of 800–900 nm, 900–1100 nm, and 1100–1600 nm vary in the material used for their fabrication as well as assembly techniques. A p–i–n photodiode is an ideal semiconductor photodetector device, because it can provide high quantum efficiency, fast response and capability to operate at higher modulation frequencies. The minimum received optical power that can be detected by a photodetector is limited by noise. A fully integrated single beam optical receiver comprises of a semiconductor photodiode, preamplifier in the electric domain, digital logic circuits, and an off-chip electronic driver circuit. This chapter discusses all the important aspects of photodetectors and optical receivers. The discussion begins with basic concepts behind the photo detection process, followed by description of different types of photodetectors usually used by optical receivers. Next, the components used in an optical receiver unit are explained. Finally, different types of noise sources in optical receivers that limit the signal-to-noise ratio, the receiver sensitivity parameter and its degradation are covered in sufficient detail.
关键词： Semiconductor Photodetectors,Noise Performance,Quantum Efficiency,Photodetectors,Avalanche Photodiode (APD),p–i–n Photodiode,Receiver Sensitivity,Responsivity,Optical Receivers
更新于2025-09-12 10:27:22
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High-Temperature Analysis of GaN-based Blue LEDs for Future Power Electronic Applications
摘要： Commercial gallium-nitride-based blue light-emitting diodes (LEDs), primarily fabricated for lighting applications, are evaluated at high temperatures (up to 700 K) for possible integration as an optocoupler emitter in high-density power electronic modules. The temperature- and injection-current-dependent internal quantum efficiency and current-voltage characteristics of the blue LEDs are studied. The internal quantum efficiency (IQE) is extracted integrated electroluminescence (EL) intensity at different temperatures using the ABC model. The presented method helps evaluate the optimized injection current density to achieve minimum deviation in LED IQE at a broader range of operating temperatures. As per the ABC model, the LED can operate at 700 K with an IQE of 58.50% when it operates at a current density of 2A/cm2. The results show that for a temperature range of 77 – 700 K, the minimum deviation of IQE occurs when the injected current density is between 1 to 10 A/cm2. Normalized external quantum efficiency (EQE) of the device at different temperatures were also extracted using the ABC model.
关键词： quantum efficiency,high-density power module,electroluminescence,optocoupler,high-temperature optoelectronics,galvanic isolation
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