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Dynamic Response-Based LEDs Health and Temperature Monitoring
摘要： this paper presents a number of novel methods to measure the junction temperature and to estimate the health of gallium nitride light-emitting diodes (LEDs). The methods are based on measurements of the dynamic impedance and optical output. Our experimental analysis reveals temperature sensitive parameters of the electrical and optical responses. Moreover, a correlation between the non-radiative current characterizing the defects in the active region and the small-signal impedance is demonstrated. The demonstrated methods can be applied to enhance existing techniques. The temperature-monitoring derived dependencies also build a foundation for advanced in-field monitoring health of the LEDs and for prediction of imminent failures using the infrastructure of visible light communication systems. Such models are valuable for predictive maintenance.
关键词： smart driver,failure modes,temperature,impedance,OWC,electrical response,optical response,defects,LED,reliability
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - On the Origin of Silicon Lifetime Degradation During Anneal in III-V Material Growth Chambers
摘要： Silicon bulk lifetime degradation in III-V material growth chambers has been a major hindrance to the development of III-V/Si tandem solar cells. While the exact mechanisms responsible for this degradation remain unknown, many researchers have attributed such degradation to extrinsic contaminants that diffuse into silicon bulk during growth. In this work, we show that thermal activation of grown-in defects in ?oat zone wafers is also a key mechanism behind such degradation. Annealing of the wafer at 1000 ?C to remove these defects, together with a SiNX diffuse barrier layer deposition are both required to preserve the silicon bulk lifetime.
关键词： grown-in defects,diffuse barrier,III-V/Si,silicon bulk lifetime degradation
更新于2025-09-23 15:19:57
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Influence of the Subcell Properties on the Fill Factor of Two-Terminal Perovskitea??Silicon Tandem Solar Cells
摘要： The performance of a tandem solar cell depends on the performance of its constituting subcells. Although this dependency is theoretically straightforward for open-circuit voltage (Voc) and short-circuit current, it is indirect for fill factor (FF) and thus for efficiency. We study here with simple simulations the effect on the tandem performance of each subcell FF by varying systematically their series resistance, parallel resistance, and local defect. We demonstrate that series resistance impacts strongly FF for single-junction devices but marginally for tandem devices, the opposite holding for parallel resistances (shunting). We show that localized defects will be most stringent to the tandem device when they occur in the current-limiting subcell. There is thus no obvious correlation between FFs of a tandem device and of its subcells. Finally, we compare two bottom-cell designs and highlight the importance of using a high-Voc bottom cell to reach high tandem efficiencies.
关键词： series resistance,tandem solar cells,parallel resistance,perovskite-silicon,local defects,fill factor
更新于2025-09-23 15:19:57
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Interplay of charge transfer and disorder in optoelectronic response in Graphene/hBN/MoS<sub>2</sub> van der Waals heterostructures
摘要： Strong optoelectronic response in the binary van der Waals heterostructures of graphene and transition metal dichalcogenides (TMDCs) is an emerging route towards high-sensitivity light sensing. While the high sensitivity is an effect of photogating of graphene due to inter-layer transfer of photo-excited carriers, the impact of intrinisic defects, such as traps and mid-gap states in the chalcogen layer remain largely unexplored. Here we employ graphene/hBN (hexagonal boron nitride)/MoS2 (molybdenum disulphide) trilayer heterostructures to explore the photogating mechanism, where the hBN layer acts as interfacial barrier to tune the charge transfer timescale. We find two new features in the photoresponse: First, an unexpected positive component in photoconductance upon illumination at short times that preceeds the conventional negative photoconductance due to charge transfer, and second, a strong negative photoresponse at infrared wavelengths (up to 1720 nm) well-below the band gap of single layer MoS2. Detailed time and gate voltage-dependence of the photoconductance indicates optically-driven charging of trap states as possible origin of these observations. The responsivity of the trilayer structure in the infrared regime was found to be extremely large (> 108 A/W at 1550 nm using 20 mV source drain bias at 180 K temperature and ≈ ?30 V back gate voltage). Our experiment demonstrates that interface engineering in the optically sensitive van der Waals heterostructures may cast crucial insight onto both inter- and intra-layer charge reorganization processes in graphene/TMDC heterostructures.
关键词： defects and disorders in TMDCs,monolayer MoS2,phototransistor,graphene,infrared photodetection,Van der Waals heterostructures
更新于2025-09-23 15:19:57
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A Study of Eu Doping in Nanolayers of CsPbBr <sub/>3</sub> using Ab Initio Calculations to Understand <i>fa??f</i> Transitions in Eu <sup>3+</sup> -Doped Nanocrystals for Light-Emitting Diodes
摘要： Recent experiments on Eu doped nanocrystals of CsPbX3 (X = Cl, Br) show that Eu exists in 3+ oxidation state even though it substitutes Pb which is in 2+ state in these perovskites. Therefore, the question arises, what is it that leads to the formation of Eu3+ in nanocrystals of these materials? In order to understand this, we have studied the doping of Eu in a slab (~1.8 nm thick) of CsPbBr3 from ab initio calculations and explored various possibilities that could lead to the formation of Eu3+ and the occurrence of f-f transitions. These include: 1) the presence of a Cs vacancy, 2) the existence of H or OH due to moisture, 3) substitution of O at a surface halogen site, and 4) the possibility of excess halogen around Eu. It is found that the presence of surface oxygen is the most likely reason for the observation of Eu3+ in these nanolayers. Our results show the presence of partially occupied spin-up f states and 6.48 μB magnetic moment on Eu that could lead to the possibility of f-f transition in these doped systems. A similar result has also been obtained for Eu doped in CsPbCl3 nanolayers. The calculated change in energy when defects/impurities are present gives favourable indication of finding H, OH, and Br as interstitials and O as substitutional entities, but Cs vacancy is unlikely. Additionally, we find that the doping of Eu in nanolayers does not affect the atomic structure and the cost of doping is also very small making these perovskites very promising materials for light emitting diodes and other solid-state lighting applications.
关键词： Two-dimensional systems,Light emitting diodes,Solid state lighting,Density functional theory,Metal-halide perovskites,Nanolayers,Defects,f-f transitions
更新于2025-09-23 15:19:57
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Formation mechanism of porous rose-like WO3 and its photoresponse and stability study
摘要： WO3 materials are widely used in photocatalysis and electrocatalysis. In this work, sodium dodecyl benzene sulfonate (SDBS) was used to control the growth of H2WO4 during chemical bath deposition fabrication process. The as-prepared H2WO4 material showed a rose-like morphology and after annealing the obtained WO3 sample was porous with oxygen defects. XRD, SEM, TEM, XPS and some other method were used to characterize the samples. A possible growth mechanism was given depending on the characterization results. The addition of SDBS resulted in a simultaneous growth of plenty H2WO4 nucleus, which caused a uniform distribution. Compared with normal WO3, the as-fabricated porous rose-like WO3 showed a higher stability to photocorrosion and a narrower band gap.
关键词： porous,photocatalysis,electrocatalysis,oxygen defects,WO3,SDBS
更新于2025-09-23 15:19:57
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Application of Infrared Digital Holography for Characterization of Inhomogeneities and Voluminous Defects of Single Crystals on the Example of ZnGeP2
摘要： In this work, the method of IR digital holography intended for detection of volumetric defects in ZnGeP2 single crystals has been tested. The holographic method is veri?ed by a comparison of the results obtained with the data obtained by other methods. The spatial resolution of the experimental setup is ~15–20 μm. The volumetric defects of the ZnGeP2 crystal structure (in samples with thickness up to 50 mm) such as growth striations, dislocation chain, and inclusions of the second phase (Zn3P2) shaped as needles up to ~100 μm long and ~10 μm wide have been visualized by the method of IR digital holography.
关键词： digital holography,single crystals,inhomogeneities,ZnGeP2,voluminous defects
更新于2025-09-23 15:19:57
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Microstructural investigation of defects in photovoltaic cells by the electron beam-induced current method
摘要： This work aims to clarify the application of electron beam-induced current (EBIC) method for the morphological analysis and detection of local defects and impurities in semiconductor structures such as solar cells. One of the advantages of this method is to observe a leakage path and microplasma sites with nanometer resolution. This technique allows to precisely locate the a?ected area and determine the type of defect that cannot be commonly characterized with su?cient accuracy. Simultaneously, a focused ion beam could be used to determine junction by milling of the samples at the area of interest. The evaluation results of experimental measurement using these techniques on photovoltaic cells illustrates the applicability and importance of the EBIC method.
关键词： defects,solar cells,ebic,structural analysis
更新于2025-09-23 15:19:57
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Defect mediated transport in self-powered, broadband and ultrafast photoresponse of MoS <sub/>2</sub> /AlN/Si based photodetector
摘要： By combining unique properties of ultrathin 2D materials with conventional 3D semiconductors, devices with enhanced functionalities can be realized. Here we report a self-powered and ultrafast photodetector based on hybrid MoS2/AlN/Si heterostructure. The heterojunction is formed by depositing MoS2 thin film by pulsed laser deposition on AlN/Si(111) template. The vertical transport properties of the device under dark and light illumination conditions, exhibit an excellent photoresponse in a broad range of wavelengths (300–1100 nm) at 0 V. The maximum responsivity of this photodetector is found to be 9.93 A/W at wavelength of 900 nm. The device shows an ultrafast temporal response with response/recovery times of 12.5/14.9 μs. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy reveal presence of native oxygen impurities in AlN, throughout the bulk of the film. These oxygen defects form a deep donor level in AlN and play a crucial role in the transport of the photogenerated carriers, resulting in enhanced device performance.
关键词： broadband and ultrafast photoresponse,deep defects,MoS2,AlN,pulsed laser deposition
更新于2025-09-23 15:19:57
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Laser Powder Bed Fusion of Precipitation-Hardened Martensitic Stainless Steels: A Review
摘要： Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.
关键词： 17–4 stainless steel,heat treatment,microstructure,precipitation-hardened stainless steels,ferrite,selective laser melting,building atmosphere,defects,laser powder bed fusion
更新于2025-09-23 15:19:57