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- 2018
- differential low noise amplifier
- GaAs pHEMT
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Spectral response measurements of each subcell in monolithic triple-junction GaAs photovoltaic devices
摘要： Multijunction photovoltaic devices have gained attention for both solar cells and wireless power transmission. Herein, we present the spectral response of each subcell in a monolithic triple-junction photovoltaic device composed of only GaAs subcells with different thicknesses, which clarifies current matching among the GaAs subcells under simulated solar illumination conditions. In addition, the spectral response curves of each subcell show that the power-dependent spectral responses under laser illumination with wavelengths of 405, 660, and 785 nm are explained by the top GaAs subcell, which has a slightly lower shunt resistance and experiences the effects of luminescent coupling.
关键词： luminescent coupling,photovoltaic devices,spectral response,multijunction,GaAs
更新于2025-09-11 14:15:04
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Monitoring subwavelength grating structures for vertical-cavity surface-emitting laser applications by spectroscopic ellipsometry
摘要： GaAs based vertical cavity surface emitting lasers (VCSELs) have one of the fastest growing markets due to their numerous applications in imaging technology, optical sensors, and interconnects. Stable, single-mode operation of these laser diodes is often achieved by forming subwavelength structures on the surface of the GaAs semiconductor. Quick and preferably noncontact inspection of the formed nanostructures is desired during the fabrication process. Nanostructure characterization by spectral ellipsometry-based metrologies has become an indispensable tool in the semiconductor industry. An advanced method of ellipsometry is the application of Mueller-matrix ellipsometry, which enables the characterization of structure details difficult to measure or not reachable by using standard ellipsometry measurements. In this paper, the authors present the results of nanostructure characterization by model-based dimension metrology using spectral ellipsometry and Mueller-matrix spectral ellipsometry of substrates during the process of VCSEL fabrication.
关键词： Mueller-matrix ellipsometry,VCSELs,spectroscopic ellipsometry,nanostructure characterization,GaAs
更新于2025-09-11 14:15:04
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Microwave Linear Characterization Procedures of On-Wafer Scaled GaAs pHEMTs for Low-Noise Applications
摘要： This contribution deals with the microwave linear characterization and noise figure measurement of four on-wafer GaAs pseudomorphic high-electron mobility transistors having scaled gate widths. The proposed measurement campaign has been fulfilled in two different laboratories: The University of Messina, Italy and US Naval Research Laboratory, Washington, DC, USA. Two equivalent approaches have been straightforwardly employed: a standard tuner-based technique and a novel tuner-less technique. The effectiveness of the novel technique has been confirmed as carried out independently by the two laboratories, evidencing the benefits of both techniques. The proposed experimental activity highlights the applicability of the tunerless technique for the noise characterization of advanced on-wafer devices without the constraint imposed by the addition of a source tuner to the standard measurement setup.
关键词： on-wafer GaAs pHEMT,noise figure,microwave,low-noise characterization
更新于2025-09-11 14:15:04
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Efficient fluorescence quenching of CdSe quantum dots on epitaxial GaAs nanostructures
摘要： Interaction of CdSe quantum dots (QDs) with epitaxially grown GaAs nanostructures has been studied using photoluminescence (PL) technique. Highly fluorescent CdSe QDs of size 3.9 nm were synthesized by colloidal method and coated over GaAs nanostructures grown on GaAs (111)B substrate by metal organic vapor phase epitaxy (MOVPE) using self-assembled Ga droplets as catalyst. Effect of conditions like catalyst growth time and temperature on the growth of GaAs nanostructures has also been studied. Highly uniform tapered hexagonal nanostructures of height around 500 nm were obtained in nearly 100% yield at 420 °C using Ga droplets grown for 10 s. The fluorescence emission of the CdSe QDs on sample bearing the GaAs nanostructures was measured by steady state and time-resolved photoluminescence (TRPL) techniques and compared with the one obtained on bare substrate. Enhanced quenching of the fluorescence of QDs has been witnessed on the sample in which GaAs nanostructures were present. It has been attributed to more efficient defect-related non-radiative relaxation of excited QDs on the surface of six {110} side facets of the GaAs nanostructures that were not present in the bare substrate. The detailed analysis of the TRPL characteristics of the samples has suggested F?rster-like resonance energy transfer (FRET)-based relaxation of CdSe QDs on GaAs nanostructures through shallow traps with significantly reduced average lifetime and the high quenching efficiency.
关键词： Nanostructures,MOVPE,GaAs,CdSe,Time-resolved photoluminescence,Quantum dots
更新于2025-09-11 14:15:04
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An advanced approach to control the electro-optical properties of LT-GaAs-based terahertz photoconductive antenna
摘要： This work reports on an advanced approach to the design of THz photoconductive antenna (PCA). The LT-GaAs thin films used for the PCA fabrication were synthesized by MBE method on GaAs (100) substrate by adjusting the As pressure, As/Ga fluxes ratio, growth/annealing temperatures and annealing time. These parameters crucially affect electro-optical properties of the PCA samples as evidenced by the THz radiation power and time-domain spectroscopy measurements. The annealing temperature of 670 °C was found to be optimal for constructing a PCA possessing high amplitude of the THz radiation over the spectral range up to 1 THz at the resonance of 0.1 THz. The comparison of this PCA with the reference ZnTe crystal reveals a 2-fold increase in THz power. Furthermore, this antenna attains a 1.5-, 3-, and 2-fold increase in THz power, photocurrent efficiency, and actuating dc BV, as compared with the commercial ZOMEGA antenna. These results pave the way towards the creation of highly efficient LT-GaAs-based PCAs.
关键词： THz-antenna,Terahertz (THz) radiation,Photoconductive antenna (PCA),Low temperature-grown gallium arsenide (LT-GaAs),THz-spectroscopy
更新于2025-09-11 14:15:04
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Correlations between optical properties and Voronoi-cell area of quantum dots
摘要： A semiconductor quantum dot (QD) can generate highly indistinguishable single photons at a high rate. For application in quantum communication and integration in hybrid systems, control of the QD optical properties is essential. Understanding the connection between the optical properties of a QD and the growth process is therefore important. Here, we show for GaAs QDs, grown by infilling droplet-etched nanoholes, that the emission wavelength, the neutral-to-charged exciton splitting, and the diamagnetic shift are strongly correlated with the capture-zone area, an important concept from nucleation theory. We show that the capture-zone model applies to the growth of this system even in the limit of a low QD density in which atoms diffuse over μm distances. The strong correlations between the various QD parameters facilitate preselection of QDs for applications with specific requirements on the QD properties; they also suggest that a spectrally narrowed QD distribution will result if QD growth on a regular lattice can be achieved.
关键词： capture-zone model,optical properties,Voronoi-cell area,GaAs QDs,quantum dots
更新于2025-09-11 14:15:04
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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) - Suspended Epoxy Polymer Inverted Tapers for Scalable Fibre-Coupled Single-Photon Devices
摘要： The combination of integrated nanophotonic circuits and single quantum emitters holds great promise for scalable quantum information processing (QIP) and for the realization of photonic quantum networks. Efficient and deterministic sources of highly-pure and indistinguishable single photons have been demonstrated using quantum dots (QDs) in GaAs nanostructures [1], enabling the integration with planar circuitry. However, the efficient out-coupling of light from the chip into optical fibres, required for communication with distant quantum nodes and photon storage, remains a challenging task. Here, we report a spot-size converter for the end-fire coupling between suspended GaAs waveguides with embedded QDs and lensed fibres.
关键词： spot-size converter,single-photon sources,photonic quantum networks,quantum dots,GaAs nanostructures
更新于2025-09-11 14:15:04
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Quantum Dots - Theory and Applications || Quantum Dots Prepared by Droplet Epitaxial Method
摘要： In this work, we are dealing with the droplet epitaxially prepared quantum dots. This technology is not only an alternative way of the strain induced technique to prepare quantum dots, but it allows us to make various shaped nano structures from various material. The present paper deals not only with the so called conventional shaped quantum dot but also with the ring shaped dot, with the inverted dot and with dot molecules as well. Their thechnology, opto-electronical and the structural properties are also discussed.
关键词： MBE,QD,AlGaAs,droplet epitaxy,AlAs,GaAs
更新于2025-09-11 14:15:04
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Photoluminescence characteristics of InGaP/GaAs dual-junction solar cells under current mismatch conditions
摘要： Current mismatch is a critical factor for impairing the conversion efficiency of multi-junction solar cells. Herein, we find a visual phenomenon to distinguish whether the InGaP/GaAs dual-junction solar cell is undergoing current mismatch. It is found that the device at short circuit emits red light under the multiple-source solar simulator when the incident power of the first light source is high. Furthermore, the similar photoluminescence characteristic is also observed when two different lasers are used. These results exhibit that the photoluminescence phenomenon is a facile method to identify the current mismatch of multi-junction solar cells.
关键词： dual-junction solar cells,photoluminescence,current mismatch,InGaP/GaAs
更新于2025-09-11 14:15:04
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Photoluminescence properties as a function of growth mechanism for GaSb/GaAs quantum dots grown on Ge substrates
摘要： In this work, we use photoluminescence (PL) spectroscopy to investigate how self-assembled GaSb/GaAs quantum dots (QDs) depend on their growth mechanism. Carrier transfer (i.e., carrier recombination in QDs and escape through the barrier layer) is investigated as a function of excitation-power- and temperature-dependent PL measurements. A drastic blueshift of the QD peak energy from 1.23 to 1.30 eV and a further shift to 1.33 eV reveal the influence of the GaSb growth rate and the growth temperature on the optical properties of these QDs. The thermal activation energy is extracted from the temperature-dependent PL by fitting the integrated PL intensity of the QD peaks to the Arrhenius relation. The QDs grown at the growth rate of 0.1 monolayers/s at 450 °C have higher thermal activation energy (109 meV) than those grown at a lower growth rate and higher QD growth temperature. The observed PL characteristics are discussed in terms of QD size, uniformity of QDs, and material intermixing occurring during QD growth on the buffer layer and capping layer.
关键词： Ge substrates,quantum dots,photoluminescence,GaSb/GaAs,growth mechanism
更新于2025-09-11 14:15:04