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Full Activation of Boron in Silicon Doped by Self-assembled Molecular Monolayers
摘要： The self-assembled molecular monolayer (SAMM) doping has great potential in state-of-the-art nanoelectronics with unique features of atomically precision and non-destructive doping on complex 3D surfaces. However, it was recently found that carbon impurities introduced by the SAMM significantly reduced the activation rate of phosphorus dopants by forming majority carrier traps. Developing a defect-free SAMM doping technique with a high activation rate for dopants becomes critical for reliable applications. Considering that susbstitutional boron does not interact with carbon in silicon, herein we employ Hall measurements and secondary ion mass spectrometry (SIMS) to investigate boron activation rate, and then deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) to analyze defects in boron-doped silicon by the SAMM technique. Unlike the phosphorus dopants, the activation rate of boron dopants is close to 100%, which is consistent with the defect measurement results (DLTS and MCTS). Only less than 1% boron dopants bind with oxygen impurities, forming majority hole traps. Interestingly carbon-related defects in form of CsH and CsOH act as minority trap states in boron-doped silicon which will only capture electrons. As a result, the high concentration of carbon impurities have no impact on the activation rate of boron dopants.
关键词： boron-doped silicon,Full activation,molecular monolayer doping,carbon-related defects,minority carrier trap
更新于2025-09-12 10:27:22
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Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current
摘要： Organic photodetectors (OPDs) have gained increasing interest as they offer cost-effective fabrication methods using low temperature processes, making them particularly attractive for large area image detectors on lightweight flexible plastic substrates. Moreover, their photophysical and optoelectronic properties can be tuned both at a material and device level. Visible-light OPDs are proposed for use in indirect-conversion X-ray detectors, fingerprint scanners, and intelligent surfaces for gesture recognition. Near-infrared OPDs find applications in biomedical imaging and optical communications. For most applications, minimizing the OPD dark current density (Jd) is crucial to improve important figures of merits such as the signal-to-noise ratio, the linear dynamic range, and the specific detectivity (D*). Here, a quantitative analysis of the intrinsic dark current processes shows that charge injection from the electrodes is the dominant contribution to Jd in OPDs. Jd reduction is typically addressed by fine-tuning the active layer energetics and stratification or by using charge blocking layers. Yet, most experimental Jd values are higher than the calculated intrinsic limit. Possible reasons for this deviation are discussed, including extrinsic defects in the photoactive layer and the presence of trap states. This provides the reader with guidelines to improve the OPD performances in view of imaging applications.
关键词： large area image sensors,charge injection,trap states,dark current,flexible image sensors,organic photodetectors
更新于2025-09-12 10:27:22
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Sensitivity of Sub-bandgap External Quantum Efficiency Measurements of Solar Cells under Electrical and Light Bias
摘要： The measurement of the external quantum efficiency (EQE) for photo-current generation at photon energies below the bandgap of semiconductors has always been an important tool for understanding phenomena such as Urbach tail and trap state dynamics. The shape of the sub-gap EQE can also reveal the subtle but important physics of inter-and-intramolecular states that lay at the heart of charge photogeneration in molecular systems such as organic semiconductors. In this work, we examine the influence of optical and electrical noise on the sensitivity of EQE measurements under different electrical and optical bias conditions and demonstrate how to enhance the dynamic range to an unprecedented >100 dB. We identify and study several apparatus-and-device-related factors limiting the sensitivity including: the electrical noise floor of measurement system; flicker and pick-up noise; illumination source stray light; the photon noise of the light bias source; the electrical noise of the voltage bias source; and shunt-resistance-limited thermal and electrical shot noise of the device. By understanding and minimizing the influence of these factors we are able to detect EQE signals derived from weak sub-gap absorption features in both organic and inorganic solar cell systems at photon energies well below their bandgaps. We area also able to observe sub-gap low finesse cavity interference effects which are sometimes confused with, for example, directly stimulated charge transfer state photo-current.
关键词： Photocurrent spectroscopy,Sub-bandgap absorption,Sensitive external quantum efficiency,Trap states,Solar cells,Charge transfer states
更新于2025-09-12 10:27:22
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Laser drilling of micro-holes in single crystal silicon, indium phosphide and indium antimonide using a continuous wave (CW) 1070 nm fibre laser with millisecond pulse widths
摘要： The laser micro-drilling of “thru” holes, also known as via holes, in Si, InP and InSb semiconductor wafers was studied using millisecond pulse lengths from an IPG Laser Model YLR-2000 CW multimode 2 kW Ytterbium Fibre Laser and a JK400 (400 W) fibre laser, both with 1070 nm wavelength. The flexibility of this laser wavelength and simple pulsing scheme were demonstrated for semiconductor substrates of narrow (InSb Eg 0.17 eV) and wide (InP Eg 1.35 eV)) room-temperature bandgap, Eg, with respect to the photon energy of 1.1 eV. Optical microscopy and cross-sectional analysis were used to quantify hole dimensions and the distribution of recast material for all wafers and, for silicon, any microcracking for both (100) and (111) single crystal surface Si wafer orientations. It was found that the thermal diffusivity was not a sufficient parameter for predicting the relative hole sizes for the Si, InP and InSb single crystal semiconductors studied. Detailed observations for Si showed that, between the threshold energies for surface melting and the irradiance for drilling a “thru” hole from the front surface to rear surface, there was a range of irradiances for which micro-cracking occurred near the hole circumference. The directionality and lengths of these microcracks were studied for the (100) and (111) orientations and possible mechanisms for formation were discussed, including the Griffith criterion for microcracks and the failure mechanism of fatigue usually applied to welding of metals. For Si, above the irradiance for formation of a thru-hole, few cracks were observed. Future work will compare similar observations and measurements in other narrow- and wide-bandgap semiconductor wafer substrates. We demonstrated one application of this laser micro-drilling process for the micro-fabrication of a thru hole precisely-located in the centre of a silicon-based atom chip which had been patterned using semiconductor lithographic techniques. The end-user application was a source of magneto-optically trapped (MOT) cold atoms of Rubidium (87Rb) for portable quantum sensing.
关键词： microcrack,InP,Si,Griffith criterion,pulse,atom chip,Ytterbium fibre laser,semiconductor material,Fibre laser,semiconductor wafer,laser drilling,silicon,magneto-optical trap,MOT,via hole,laser micro-drilling,cold atoms,InSb,thru hole
更新于2025-09-12 10:27:22
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A Heat Pipe Cooler for High Power LED’s Cooling in Harsh Conditions
摘要： The paper presents an innovative method for High Power LEDs cooling in harsh conditions. To take full advantage of the benefits of LEDs, proper thermal management must be realized. This paper describes the limits of the cooling solution based on heat pipe, to maintain the junction temperature close to the nominal value, to avoid the color shift, recoverable light output reduction, voltage decreases. The most important, the reliability of any LED is a direct function of junction temperature, knowing that the higher the junction temperature, the shorter the lifetime of the LED.
关键词： LED Cooling,Energy Efficiency.,Heat-Trap,Heat Pipe
更新于2025-09-12 10:27:22
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Tuning methylammonium iodide amount in organolead halide perovskite materials by post-treatment for high-efficiency solar cells
摘要： In this study, the composition of organic-inorganic perovskite materials is tuned by methylammonium iodide (MAI) post-treatment for high photovoltaic performance. By spin-coating MAI solutions of different concentrations, the amounts of PbI2 and MAI in perovskite layers are tuned. In perovskites, the removal of PbI2 through a reaction with MAI decreases the hysteresis in photocurrent density-voltage curves. Further, by treating perovskites with a high-concentration MAI solution, the excess MAI is incorporated into the perovskites. These perovskites with excess MAI show better power conversion efficiencies (of up to 20.7%) than perovskites with excess PbI2, because of the decrease in trap density. Since the present post-treatment can control perovskite composition without affecting the morphology and crystallinity of the perovskite crystals, this technique would be a useful tool to improve the photovoltaic performance of perovskite solar cells.
关键词： ion composition,performance enhancement,perovskite solar cells,trap density,surface treatment
更新于2025-09-12 10:27:22
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Evidence of trap-assisted Auger recombination in low radiative efficiency MBE-grown III-nitride LEDs
摘要： By studying low radiative e?ciency blue III-nitride light emitting diodes (LEDs), we ?nd that the ABC model of recombination commonly used for understanding e?ciency behavior in LEDs is insu?cient and that additional e?ects should be taken into account. We propose a modi?cation to the standard recombination model by incorporating a bimolecular nonradiative term. The modi?ed model is shown to be in much better agreement with the radiative e?ciency data and to be more consistent than the conventional model with very short carrier lifetimes measured by time-resolved photoluminescence in similar, low radiative e?ciency material. We present experimental evidence that a hot carrier-generating process is occurring within these devices, in the form of measurements of forward photocurrent under forward bias. The forward photocurrent, due to hot carrier generation in the active region, is present despite the lack of any “e?ciency droop”—the usual signature of band-to-band Auger recombination in high-quality III-nitride LEDs. Hot carrier generation in the absence of band-to-band Auger recombination implies that some other source of hot carriers exists within these low radiative e?ciency devices, such as trap-assisted Auger recombination.
关键词： hot carrier generation,III-nitride LEDs,ABC model,trap-assisted Auger recombination,radiative efficiency
更新于2025-09-12 10:27:22
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Production of highly charged ions of rare species by laser-induced desorption inside an electron beam ion trap
摘要： This paper reports on the development and testing of a novel, highly efficient technique for the injection of very rare species into electron beam ion traps (EBITs) for the production of highly charged ions (HCI). It relies on in-trap laser-induced desorption of atoms from a sample brought very close to the electron beam resulting in a very high capture efficiency in the EBIT. We have demonstrated a steady production of HCI of the stable isotope 165Ho from samples of only 1012 atoms (～300 pg) in charge states up to 45+. HCI of these species can be subsequently extracted for use in other experiments or stored in the trapping volume of the EBIT for spectroscopic measurements. The high efficiency of this technique extends the range of rare isotope HCIs available for high-precision atomic mass and spectroscopic measurements. A first application of this technique is the production of HCI of the synthetic radioisotope 163Ho for a high-precision measurement of the QEC-value of the electron capture in 163Ho within the “Electron Capture in Holmium” experiment [L. Gastaldo et al., J. Low Temp. Phys. 176, 876–884 (2014); L. Gastaldo et al., Eur. Phys. J.: Spec. Top. 226, 1623–1694 (2017)] (ECHo collaboration) ultimately leading to a measurement of the electron neutrino mass with an uncertainty on the sub electronvolt level.
关键词： high-precision atomic mass measurements,highly charged ions,spectroscopic measurements,rare isotopes,electron beam ion trap,laser-induced desorption
更新于2025-09-12 10:27:22
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Simulating nanocrystal-based solar cells: A lead sulfide case study
摘要： Nanocrystal-based solar cells are promising candidates for next generation photovoltaic applications; however, the most recent improvements to the device chemistry and architecture have been mostly trial-and-error based advancements. Due to complex interdependencies among parameters, determining factors that limit overall solar cell efficiency are not trivial. Furthermore, many of the underlying chemical and physical parameters of nanocrystal-based solar cells have only recently been understood and quantified. Here, we show that this new understanding of interfaces, transport, and origin of trap states in nanocrystal-based semiconductors can be integrated into simulation tools, based on 1D drift-diffusion models. Using input parameters measured in independent experiments, we find excellent agreement between experimentally measured and simulated PbS nanocrystal solar cell behavior without having to fit any parameters. We then use this simulation to understand the impact of interfaces, charge carrier mobility, and trap-assisted recombination on nanocrystal performance. We find that careful engineering of the interface between the nanocrystals and the current collector is crucial for an optimal open-circuit voltage. We also show that in the regime of trap-state densities found in PbS nanocrystal solar cells (～1017 cm?3), device performance exhibits strong dependence on the trap state density, explaining the sensitivity of power conversion efficiency to small changes in nanocrystal synthesis and nanocrystal thin-film deposition that has been reported in the literature. Based on these findings, we propose a systematic approach to nanocrystal solar cell optimization. Our method for incorporating parameters into simulations presented and validated here can be adopted to speed up the understanding and development of all types of nanocrystal-based solar cells.
关键词： nanocrystal-based solar cells,simulation,charge carrier mobility,lead sulfide,drift-diffusion models,trap states
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Viscoelasticity Measurements by an Optofluidic Micro-Rheometer
摘要： During the last decades, microrheology attracted a significant attention thanks to the possibility of investigating the viscoelastic properties of complex systems (e.g. cells and soft materials) at micrometer scale. The inherent low-consumption of sample offered by microrheology makes it the ideal candidate to study the rheological properties of precious/limited materials. In active microrheology, optical or magnetic forces enable trapping and manipulation of micro-probes in the fluid under test. The probe’s response to external stimuli is used to derive the rheological properties of the surrounding medium. While this approach has been already reported in the scientific literature mainly using optical tweezers [1], in this document we propose a different system configuration based on a dual beam laser trap, previously exploited to realize a simple viscometer [2,3]. The here proposed device has all the features of a rheometer, also allowing to measure the elastic properties, and has the advantage of requiring a lower beam intensity while being able to apply larger forces with respect to standard optical tweezers. Additionally the system can be easily integrated in a glass substrate, requiring just an external connection to a CW-laser source and a low-magnification objective for sample observation.
关键词： optical tweezers,dual beam laser trap,microrheology,viscoelastic properties,rheometer
更新于2025-09-12 10:27:22