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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - High Dynamic Range Infrared Sensors for Remote Sensing Applications
摘要： In this presentation, we will report our recent efforts in achieving high performance in Antimonides type-II superlattice (T2SL) based infrared photodetectors using the barrier infrared detector (BIRD) architecture. The recent emergence of barrier infrared detectors such as the nBn [1] and the XBn [2] have resulted in mid-wave infrared (MWIR) and long-wave infrared (LWIR) detectors with substantially higher operating temperatures than previously available in III-V semiconductor based MWIR and LWIR detectors. The initial nBn devices used either InAs absorber grown on InAs substrate, or lattice-matched InAsSb alloy grown on GaSb substrate, with cutoff wavelengths of ~3.2 μm and ~4 μm, respectively. While these detectors could operate at much higher temperatures than existing MWIR detectors based on InSb, their spectral responses do not cover the full (3 – 5.5 μm) MWIR atmospheric transmission window. There also have been nBn detectors based on the InAs/GaSb T2SL absorber [3,4].
关键词： infrared detector,focal plane array,type-II superlattice,high dynamic range,high quantum efficiency
更新于2025-09-10 09:29:36
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Charge and thermal modeling of a semiconductor-based optical refrigerator
摘要： Despite multiple attempts to achieve optical refrigeration in very high (99.5%) external quantum efficiency (EQE) GaAs, no cooling has been observed to date. In this study, we investigate optical refrigeration in GaAs by numerically solving the transient drift-diffusion equation coupled to Poisson’s equation. The charge carrier distributions we obtain, together with the heat diffusion equation, allow us to observe the spatial and temporal evolution of cooling/heating within GaAs. Our results indicate that maximum cooling occurs at a laser intensity different from that which maximizes EQE. An 11-fold difference in intensity exists with a corresponding 6-fold difference in cooling power. We ultimately find that samples suspended in vacuum using a 250 lm SiO2 fiber cool to 88 K, starting from room temperature. These results emphasize the critical importance of choosing an appropriate laser excitation intensity to achieve optical refrigeration along with minimizing the conductive heat load on the refrigerator. Furthermore, results of this study are applicable towards analyzing the optical response of other optoelectronic systems where accurate charge and/or heat diffusion modeling is critical.
关键词： drift-diffusion equation,external quantum efficiency,Poisson’s equation,cooling power,optical refrigeration,heat diffusion equation,GaAs
更新于2025-09-10 09:29:36
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Lead-Free Direct Bandgap Double Perovskite Nanocrystals with Bright Dual-Color Emission
摘要： Lead-free double perovskite nanocrystals (NCs), i.e. Cs2AgInxBi1?xCl6 (x = 0, 0.25, 0.5 0.75 and 0.9), that can be tuned from the indirect bandgap (x = 0, 0.25 and 0.5) to the direct bandgap (x = 0.75 and 0.9) are designed. Direct-bandgap NCs exhibit 3 times greater absorption cross-section, lower sub-bandgap trap states, and >5 times photoluminescence quantum efficiency (PLQE) compared with those observed for indirect bandgap NCs (Cs2AgBiCl6). A PLQE of 36.6% for direct bandgap NCs is comparable to those observed for lead-perovskite NCs in the violet region. Besides the band edge violet emission, the direct bandgap NCs exhibit bright orange (570 nm) emission. Density functional theory calculations suggesting forbidden transition is responsible for the orange emission, which is supported by time resolved PL and PL excitation spectra. The successful design of lead-free direct bandgap perovskite NCs with superior optical properties opens the door for high performance lead-free perovskite optoelectronic devices.
关键词： dual-color emission,direct bandgap,Lead-free,photoluminescence quantum efficiency,double perovskite nanocrystals
更新于2025-09-09 09:28:46
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[IEEE 2018 15th International Conference on Smart Cities: Improving Quality of Life Using ICT & IoT (HONET-ICT) - Islamabad, Pakistan (2018.10.8-2018.10.10)] 2018 15th International Conference on Smart Cities: Improving Quality of Life Using ICT & IoT (HONET-ICT) - Two Dimensional Materials based Heterostructures for Photosensing Applications
摘要： Graphene (Gr) and transition metal dichalcogenides (TMDC) have wide scope in electronic and optoelectronic incredible optical and electrical properties. The study investigates the utilization of molybdenum disulfide-graphene (MoS2-Gr) hybrid field effect transistor (FET) as photosensor. The photo-current response of hybrid FET was studied for source-drain voltages(Vds) range from 1 to 5 V. The important optical figure of merits such as photoresponsivity (R(cid:2)) and external quantum efficiency (EQE) are calculated to evaluate the performance of FET. Enhancement in the optical performance of FET is observed. MoS2-Gr divulges high R(cid:2) (3.34×103 AW-1) while the EQE of hybrid FET (1.8×104) is higher than that of individual structures. This methodology of fabricating TMDCs-Gr based hybrid devices opens new doors for advances in highly efficient photosensor for sensing and optoelectronic applications.
关键词： external quantum efficiency,photoresponsivity,Gaphene,hybrid structure,molybednum disulfide
更新于2025-09-09 09:28:46
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Excitation power dependence of Eu3+ photoluminescence in barium borate glass
摘要： Eu3+-doped barium borate glasses are analysed for their optical and excitation power dependent luminescence properties. The glasses, doped with different concentrations of the lanthanide ion Eu3+, provide photoluminescence quantum efficiencies higher than 80% and, show a bright luminescence in the red spectral range, making them attractive for lighting applications.
关键词： Eu3+,lighting applications,barium borate glass,photoluminescence,quantum efficiency
更新于2025-09-09 09:28:46
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[Papers] Quantum Efficiency Simulation and Electrical Cross-talk Index Development with Monte-Carlo Simulation Based on Boltzmann Transport Equation
摘要： This paper explains a new method to model a photodiode for accurate quantum efficiency simulation. Individual photo-generated particles are modeled by Boltzmann transport equation, and simulated by Monte-Carlo method. Good accuracy is confirmed in terms of similarities of quantum efficiency curves, as well as color correction matrices and SNR10s. Three attributes - "initial energy of the electron", "recombination of electrons at the silicon surface" and "impurity scattering" - are tested to examine their effectiveness in the new model. The theoretical difference to the conventional method with drift-diffusion equation is discussed as well. Using the simulation result, the relationship among the cross-talk, potential barrier, and distance from the boundary has been studied to develop a guideline for cross-talk suppression. It is found that a product of the normal distance from the pixel boundary and the electric field perpendicular to the Z-axis needs to be more than 0.02V to suppress the probability of electron leakage to the adjacent pixel to less than 10%.
关键词： cross-talk,quantum efficiency,simulation,image sensor,BTE,Boltzmann transport equation
更新于2025-09-09 09:28:46
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The Quantum Efficiency of Charge Transfer Competing Against Non-Exponential Processes: The Case of Electron Transfer from CdS Nanorods to Hydrogenase
摘要： Photoexcited charge transfer from semiconductor nanocrystals to charge acceptors is a key step for photon energy conversion in semiconductor nanocrystal-based light-harvesting systems. Charge transfer competes against relaxation processes within the nanocrystals, and this competition determines the quantum efficiency of charge transfer. The quantum efficiency is a critical design element in photochemistry, but in nanocrystal–acceptor systems its extraction from experimental data is complicated by sample heterogeneity and intrinsically non-exponential excited-state decay pathways. In this manuscript, we systematically explore these complexities using TA spectroscopy over a broad range of timescales to probe electron transfer from CdS nanorods to the redox enzyme hydrogenase. To analyze the experimental data, we build a model that quantifies the quantum efficiency of charge transfer in the face of competing, potentially non-exponential, relaxation processes. Our approach can be applied to calculate the efficiency of charge or energy transfer in any donor–acceptor system that exhibits non-exponential donor decay and any ensemble distribution in the number of acceptors provided that donor relaxation and charge transfer can be described as independent, parallel decay pathways. We apply this analysis to our experimental system and unveil the connections between particle morphology and quantum efficiency. Our model predicts a finite quantum efficiency even when the mean recombination time diverges, as it does in CdS nanostructures with spatially separated electron–hole pairs that recombine with power-law dynamics. We contrast our approach to the widely-used expressions for the quantum efficiency based on average lifetimes, which for our system overestimate the quantum efficiency. The approach developed here is straightforward to implement and should be applicable to a wide range of systems.
关键词： electron transfer,quantum efficiency,semiconductor nanocrystals,non-exponential processes,charge transfer,hydrogenase,CdS nanorods
更新于2025-09-04 15:30:14
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The study of quantum efficiency in PIN photodiodes in terms of temperature and capacitive effects under non-uniform illumination conditions
摘要： In this article the impacts of quantum efficiency and bandwidth of PIN photodiodes under non-uniform illumination conditions are investigated. An absorption region is divided into the number of arbitrary layers and the continuity equations for each layer are solved with assuming that the carrier’s drift velocity is constant in each layer. Also the impact of transit time and capacitive effects of bandwidth were studied with considering the bias voltage, width of absorption region and temperature. The results show that with considering the capacitive effects, the bandwidth is increased by increase in temperature and bias voltage. We observe the effect of incident optical radiation from two n and p sides and also its impact on bandwidth and quantum efficiency. The results show more impact of radiation from n region compared to p region.
关键词： Temperature,Capacitive effect,PIN photodiode,Quantum efficiency,Bandwidth
更新于2025-09-04 15:30:14
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Multi-Color Luminescent m-LaPO <sub/>4</sub> :Ce/Tb Monospheres of High Efficiency via Topotactic Phase Transition and Elucidation of Energy Interaction
摘要： Monoclinic (m-) structured (La0.96?xCe0.04Tbx)PO4 phosphor monospheres (x = 0?0.12) of excellent dispersion and morphology uniformity were calcined (≥600 °C) from their precipitated precursor spheres (～2.0 μm) of a hexagonal (h-) structure for efficient and multicolor luminescence. The h → m phase transition, driven by dehydration, was originally proposed to proceed in a topotactic manner, which involves displacement of the RE-O polyhedra (RE: rare-earth) along the a/b axis and slight expansion of the {010} and {100} interplanar spacings of the hydrated h-phase to form the {120} and {100} planes of the anhydrous m-phase, respectively. Analysis of the energy process involving the optically active Ce3+ and Tb3+ ions found efficient Ce3+ → Tb3+ energy transfer occurring via electric dipole?quadrupole interaction, whose efficiency reached the highest value of ～44.48% at x = 0.10. The Tb3+ codoped phosphors simultaneously displayed the characteristic emissions of Ce3+ (～313 nm) and Tb3+ (～545 nm) upon exciting the Ce3+ ions with 275 nm UV light, with which the emission color was finely tuned from dark blue to green by increasing the Tb3+ content. Fluorescence decay analysis found decreasing and almost constant lifetime values for the Ce3+ and Tb3+ emissions at a higher Tb3+ content, respectively, and the phosphor presented the highest external quantum efficiency of ～84.67% at x = 0.10. The excellent luminescent performance and morphology uniformity may allow the monospheres to find application in lighting and display technologies.
关键词： LaPO4,Ce/Tb,energy transfer,multicolor luminescence,quantum efficiency,Monoclinic
更新于2025-09-04 15:30:14
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-related Materials
摘要： Dominant recombination paths in AlN and AlxGa1?xN-related structures are investigated using cathodoluminescence (CL) mapping measurements and photoluminescence (PL) spectroscopy. The dark spot contrasts originating from nonradiative recombination at threading dislocations (TDs), which are observed in CL intensity maps, drastically decrease upon elevating the temperature. This is because carriers can reach TDs at low temperatures (9–60 K), but are captured by point defects (PDs) even in the vicinity of TDs near RT. Calculations based on the experimental results indicate that in the current AlN and Al-rich AlxGa1?xN crystals, TDs scarcely affect the internal quantum efficiency (IQE) at RT as long as the TD density is less than 2.6 × 1010 cm?2. Because a TD density less than 2.6 × 1010 cm?2 has already been achieved even for heteroepitaxially grown AlN films on sapphire substrates, it is evident that the most effective method to further improve the IQE of AlxGa1?xN-related materials is to reduce PDs not TDs. Moreover, we clarify the existence of two types of PD states, which mainly degrade the emission efficiency, using temperature-dependent PL measurements. Combining the CL and PL results allows the activation energies of these PDs and TDs to be evaluated. Furthermore, we highlight the probability that PDs, which predominantly act as nonradiative recombination centers at room temperature, are complexes formed by Al vacancies and oxygen impurities that enhance the deep-level emissions at 3.2 and 3.5–3.7 eV near room temperature. Such a large impact of PDs on the efficiency degradation may be attributed to the high density of Al-vacancy–related PDs in AlN and Al-rich AlxGa1?xN compared with that of Ga-vacancy–related PDs in GaN due to the small formation energy.
关键词： AlxGa1?xN,cathodoluminescence,internal quantum efficiency,point defects,photoluminescence,nonradiative recombination,AlN,threading dislocations
更新于2025-09-04 15:30:14