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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) - Improved Photoabsorption in Thin Gallium Arsenide Solar Cells using Light Trapping Techniques
摘要： Thin absorbers for space photovoltaics can achieve higher radiation tolerance, however, they suffer from reduced photoabsorption as the active region is thinned. In this work, increasing the photoabsorption in thin single junction n-i-p GaAs solar cells have been investigated by applying different light trapping structures at the rear of the cell. The main focus has been to develop a random surface texture that varies in three dimensions to increase light scattering and the effective optical path length. From the EQE, the random back surface reflector was successfully applied to a 1.1 μm thick GaAs solar cell which resulted in a notable 38% increase in current output, when compared to the GaAs baseline cell on its substrate without a BSR. The random texture has shown the capability to maintain the current output in the 1.1 μm thick GaAs absorber and shows promise for enhancing the photoabsorption in thin GaAs absorbers that approach the sub-μm thickness regime.
关键词： photoabsorption,thin GaAs solar cells,light trapping,random maskless texture,radiation tolerance
更新于2025-09-16 10:30:52
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Interfacea??Induced High Responsivity in Hybrid Graphene/GaAs Photodetector
摘要： Photodetectors based on two-dimensional (2D)/ three-dimensional (3D) semiconductor heterojunction structures are emerging as appealing candidates for high-sensitivity applications. The performances of these hybrid photodetectors are closely correlated with their current gain mechanism. Carrier recirculation is the most commonly reported mechanism. Recently, a Fermi level alignment mechanism was proposed for 2D graphene/0-dimensional (0D) quantum dot heterostructures because of the easy Fermi level tunability of the quantum dot. In this article, an interface-induced gain mechanism using this Fermi level alignment process is proposed and identified based on a 2D graphene/3D GaAs hybrid structure with comparative measurement configurations. Because of the high surface state density of GaAs, the photo-excited holes tend to become trapped at the graphene/GaAs interface, which can easily lower the interface Fermi level and the Fermi level in graphene via an alignment process. When combined with the high carrier mobility characteristics of graphene, a maximum current gain of 2520 and responsivity of 1321 A W?1 are achieved in the devices. This study clarifies the role of the interface states in the gain characteristics of some 2D/3D hybrid devices, with results that are instructive for optimal device design.
关键词： interface-induced gain,GaAs,responsivity,photodetectors,graphene
更新于2025-09-16 10:30:52
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Numerical Simulation of GaAs Solar Cell Aging Under Electron and Proton Irradiation
摘要： Though gallium arsenide (GaAs) solar cells are proven to be relatively stable in space working conditions, they are prone to the effects of aging, which deteriorate their characteristics. The lifetime of solar cells is restricted by the degree of radiation damage that they receive. This important factor affects the performance of solar cells in practical applications. The aim of this article is to investigate by numerical simulation on the influence of aging on the main characteristics of GaAs solar cells in the space. Degradations of the electrical characteristics are simulated for over a period of 15 years. The atmosphere (AM0) conversion efficiency decreases with time from 19.08% for the unirradiated cells to 10.38% in 15 years of the mission in space. Even with low doses of particle irradiation, the performance is significantly reduced subsequent to usage over the period of 15 years of the mission in space. Numerical simulation results also reveal that the short-circuit current, the open-circuit voltage, and the conversion efficiency decline gradually with time. Moreover, the calculated evolutions are in good agreement with the measured behaviors of GaAs-based solar cells embedded in geostationary satellites during the Navigation Technology Satellite 2 (NTS-2), the Engineering Test Satellite V (ETS-V), and the NAVigation Satellite Timing And Ranging (NAVSTAR) missions, which substantiate the introduced aging law accounting for both the cumulated doses of particles and the different electron and hole traps in the structure.
关键词： space application,model,Degradation,gallium arsenide (GaAs) solar cell
更新于2025-09-12 10:27:22
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Solution Processed MoS<sub>2</sub> Quantum Dots/GaAs Vertical Heterostructures based Self-powered Photodetectors with Superior Detectivity
摘要： The characteristics of a novel 0D/3D heterojunction photodetector fabricated using solution processed colloidal MoS2 quantum dots (QDs) on GaAs is being presented. MoS2 QDs with a dimension of ~2 nm, synthesized by standard sono-chemical exfoliation process of 2D layers have been used for the purpose. The microscopic and spectroscopic studies confirmed the formation of semiconducting (2H phase) MoS2 QDs. The photodetectors were fabricated using n-GaAs substrates with two different doping concentrations resulting in n-n heterojunctions between n-type 0D MoS2 QDs and bulk n-GaAs. The devices fabricated using GaAs having higher doping concentration, upon illumination, showed an increase of reverse current of the order of ~102, while the same with lower doping concentration showed an increase of the order of ~103. All the heterojunction photodetector devices show a broadband operation over the visible wavelength range of 400 – 950 nm, with a peak responsivity of the devices being observed at 500 nm. The peak responsivity and detectivity are found to be ~400 mA/W and ~4 × 1012 Jones, respectively even without any external applied bias, which are useful for self-powered photodetection. Results indicate that colloidal MoS2/GaAs based hybrid heterostructures provide a platform for fabricating broadband photodetectors by using highly absorbing MoS2 QDs, which may show the pathway towards next-generation optoelectronic devices with superior detection properties.
关键词： MoS2,detectivity,quantum dots,photodetectors,vertical heterostructure,GaAs
更新于2025-09-12 10:27:22
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Nitrogen oxides sensing performance of thiols and dithiols self-assembled monolayer functionalized Au/GaAs-based Schottky diodes
摘要： In this work, GaAs-based Schottky diodes, functionalized by alkanethiolates, were used to fabricate NOx gas sensors with high-selectivity and low-power. Alkanethiolates were employed to form a self-assembled monolayer (SAM) on the surface of the Au (111) Schottky contacts of the n-GaAs substrate using immersion method. The adsorption behaviors between SAM and Au (111) with different terminal (functional) groups, carbon numbers (CN), immersion times (tim), and alkanedithiol concentrations were characterized by cyclic voltammetry (CV) measurement. The interaction between NOx molecules and SAM was determined by an ultraviolet/visible (UV-Vis) spectrophotometer. The NOx sensing performance of the studied device under proper conditions was investigated at different temperatures and NOx gas concentrations. Experimentally, at 25℃, good sensing responses of 49.6 and 35.5 in 100 ppm NO2 and NO ambiences were obtained, respectively. Furthermore, similar sensing properties of the studied device were found in air and in N2 ambience. Therefore, the studied device can be considered a promising candidate for NOx sensing applications.
关键词： Alkanedithiol,Nitrogen oxides,Gas sensors,Schottky diode,GaAs,Self-assembled monolayers (SAM)
更新于2025-09-12 10:27:22
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Two-frequency laser with distributed feedback formed by a space charge wave
摘要： The regimes of amplification and generation of optical TE waves arising on a grating formed by a space charge wave (SCW) in a plane optical waveguide based on an n-GaAs semiconductor are considered. For the perturbed n-GaAs waveguide, the reflectance and transmittance of TE modes with the same indices (m = n = 0) are calculated depending on the pump level and length of interaction between the optical and SCWs. It is shown that even with a relatively small depth of modulation of the dielectric constant (Δ?? ≈ 10?5) under conditions of high optical pumping (with an amplification factor ?? ≈ 150 cm?1) and corresponding SCW-optical interaction length, there is a possibility of not only amplification, but also generation of forward and backward optical modes at a wavelength of 10.6?μm. The results can be used to create tunable semiconductor laser generators based on the SCW-optical interaction and operating in the near and mid-IR range.
关键词： Semiconductor waveguide,GaAs,Space charge wave,Laser generation
更新于2025-09-12 10:27:22
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Monolithic integration of visible GaAs and near-infrared InGaAs for multicolor photodetectors by using high-throughput epitaxial lift-off toward high-resolution imaging systems
摘要： In this study, multicolor photodetectors (PDs) fabricated by using bulk p-i-n-based visible GaAs and near-infrared inGaAs structures were monolithically integrated through a high-throughput epitaxial lift-off (ELO) process. To perform multicolor detection in integrated structures, GaAs PDs were transferred onto inGaAs pDs by using a Y2o3 bonding layer to simultaneously detect visible and near-infrared photons and minimize the optical loss. As a result, it was found that the GaAs top PD and InGaAs bottom PD were vertically aligned without tilting in x-ray diffraction (XRD) measurement. A negligible change in the dark currents for each PD was observed in comparison with reference PDs through electrical characterization. Furthermore, through optical measurements and simulation, photoresponses were clearly revealed in the visible and near-infrared band for the material’s absorption region, respectively. Finally, we demonstrated the simultaneous multicolor detection of the visible and near-infrared region,which implies individual access to each PD without mutual interference. These results are a significant improvement for the fabrication of multicolor PDs that enables the formation of bulk-based multicolor PDs on a single substrate with a high pixel density and nearly perfect vertical alignment for high-resolution multicolor imaging.
关键词： high-resolution imaging,multicolor photodetectors,InGaAs,epitaxial lift-off,GaAs
更新于2025-09-12 10:27:22
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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) - Efficient Terahertz Detection with Perfectly-Absorbing Metasurface
摘要： We demonstrate a unique photoconductive design for terahertz (THz) detection based on a perfectly absorbing, all-dielectric metasurface. Our design exploits Mie resonances in electrically connected cubic resonators fabricated in low-temperature grown (LT) GaAs. Experimentally, the detector achieves very high contrast between ON/OFF conductivity states (107) whilst also requiring extremely low optical power for optimal operation (100 μW). We find that the Mie resonances dissipate sufficiently fast and maintain the detection bandwidth up to 3 THz.
关键词： photoconductive,terahertz detection,Mie resonances,LT-GaAs,metasurface
更新于2025-09-12 10:27:22
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High-detectivity infrared photodetector based on InAs submonolayer quantum dots grown on GaAs(001) with a 2?×?4 surface reconstruction
摘要： The submonolayer quantum dots of an infrared photodetector were grown by molecular beam epitaxy in the presence of a very low As ?ux and a 2 × 4 surface reconstruction in order to e?ectively nucleate small two-dimensional InAs islands that are required to form such nano-structures. A speci?c detectivity of 9.2 × 1010 cm Hz1/2 W?1 was obtained at 10 K with a bias of 1.0 V.
关键词： InAs submonolayer quantum dots,2 × 4 surface reconstruction,molecular beam epitaxy,infrared photodetector,GaAs(001)
更新于2025-09-12 10:27:22
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Planar‐type concentrating photovoltaics with cylindrical lenses directly integrated with thin flexible GaAs solar cells
摘要： Concentrated photovoltaics allow a reduction of expensive semiconductor materials by collecting incident light through optical elements such as lenses and/or mirrors, which usually require bulky or heavy dual‐axis solar trackers, requiring dedicated installation sites. In this paper, we report a planar‐type concentrating photovoltaics with cylindrical lenses on which flexible GaAs solar cells are directly integrated on the curvilinear surfaces. The planar‐type concentrating system maintains both a focused beam width and angle invariably onto its integrated solar cells throughout the day. Computational and experimental studies at various incident angles prove the benefits of the design. Demonstrations of a custom‐built cylindrical lens solar tracker installed on a rooftop or sidewall of a building prove the feasibility of the proposed concept.
关键词： solar tracker,flexible solar cell,cylindrical lens,concentrator photovoltaics (CPV),GaAs
更新于2025-09-12 10:27:22