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- differential low noise amplifier
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AIP Conference Proceedings [AIP Publishing SECOND INTERNATIONAL CONFERENCE ON MATERIAL SCIENCE, SMART STRUCTURES AND APPLICATIONS: ICMSS-2019 - Erode, India (21–22 November 2019)] SECOND INTERNATIONAL CONFERENCE ON MATERIAL SCIENCE, SMART STRUCTURES AND APPLICATIONS: ICMSS-2019 - Modeling of optical characteristics of near-infrared photodetectors on the basis of InAs/GaAs heterointerfaces
摘要： A mathematical model for simulation of optical and functional characteristics of InAs/GaAs heterointerfaces with one layer of InAs quantum dots has been developed. The presence of the peak of the main optical transitions in quantum dots of 1.2 eV (modeling) and 1.12 eV (experimental) is demonstrated. The experimental photoluminescence peak has a greater width (0.13 eV) at half the maximum radiation of the main transitions in quantum dots compared to the simulated one (0.06 eV). A red shift of the experimental peak by approximately 65 meV is observed, which indicates the presence of a size variance of quantum dots in the real heterointerface. The modeled distribution of the dark current-voltage characteristic at 90 K and zero shift reveals the value of the dark current density of 10-7 A/cm2, which is an order of magnitude less than the measurement results (10-6 A/cm2). The difference in the pattern of dependence distribution at negative and positive bias associated with the presence of quantum dots of larger size is observed.
关键词： quantum dots,InAs/GaAs heterointerfaces,photoluminescence,dark current-voltage characteristics
更新于2025-09-12 10:27:22
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Measurement and Analysis of Noise Spectra in Terahertz Wave Detection Utilizing Low-Temperature-Grown GaAs Photoconductive Antenna
摘要： Noise power spectral density (NPSD) in time domain terahertz (THz) wave detection systems utilizing GaAs-based photoconductive antennas (PCAs) was investigated quantitatively. The contributions of the PCA noise and the amplifier noises at the amplifier output depend strongly on the resistance of the PCA, the circuit parameters, and the frequency. The PCA has two types of noise: one can be modeled by the Johnson-Nyquist (thermal) noise for the PCA resistance, while the other has an NPSD inversely proportional to the frequency with its intensity dependent on the properties of the GaAs and the metallization. At a high frequency range ~ 100 kHz, voltage-type amplifier noise could appear if the cable capacitance between the PCA and the amplifier is large. As a result, a low-noise range tends to appear in the intermediate frequency range. In comparison with the PCAs with Ti/Au metallization, the PCAs with Pd/Ge/Ti/Au having lower contact resistance lead to lager influence of the Johnson-Nyquist noise at the output.
关键词： Thermal noise,Noise spectra,Photoconductive antenna,Low-temperature-grown GaAs,1/f noise
更新于2025-09-12 10:27:22
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Enhanced terahertz radiation of photoconductive antenna fabricated on GaAs-on-sapphire
摘要： The terahertz (THz) radiation properties of a photoconductive antenna (PCA) fabricated on a GaAs-on-sapphire (GoS) substrate are reported at sub-THz band. The GaAs layer with a thickness of approximately 1 μm was directly deposited on a sapphire wafer by means of molecular beam epitaxy. A butterfly-shaped antenna structure was then fabricated on the GoS substrate by photolithography, and the device was tested as the emitter of an in-house built THz time-domain spectrometer. The performance of this antenna was compared with a commercial one, which had an identical antenna structure but was fabricated on low-temperature-grown GaAs (LT-GaAs). The results showed that the GoS-based PCA radiated an enhanced THz field, which could be as much as 1.9 times that of the LT-GaAs-based PCA, indicating that GoS could be a promising photoconductive material. In addition, the optical transparency of the sapphire substrate allows the device to be illuminated from the backside, which is crucial for THz near-field imaging applications where the sample is usually in close proximity to the front surface of the PCA device.
关键词： photoconductive antenna,molecular beam epitaxy,THz time-domain spectrometer,terahertz,GaAs-on-sapphire
更新于2025-09-12 10:27:22
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Formation and characterization of charge coupled structure of polyoxometalate particles and a GaAs-based nanowire for readout of molecular charge states
摘要： To investigate the molecular charge dynamics of polyoxometalate (POM) molecules, we formed and characterized a charge coupled structure with POM molecular particles and a GaAs-based nanowire. In our system, the charge sensitivity was locally increased by capacitive coupling between a metal tip and the POM particle. Surface dispersion of POM particles on the GaAs nanowire was carried out in a controlled manner by choosing an appropriate solvent and POM concentration. We found that, after POM surface dispersion, the current in the GaAs nanowire remarkably increased by charging the POM particles using a conductive atomic force microscopy tip. The current change strongly depended on humidity of the measurement environment. The nanowire current under capacitive coupling between the conductive tip and the POM particle on the nanowire surface showed steps with a height of approximately 70 nA, suggesting that multiple hole charging and discharging occurred in the particle in a synchronized manner.
关键词： conductive atomic force microscopy,GaAs-based nanowire,molecular charge states,charge coupled structure,polyoxometalate
更新于2025-09-11 14:15:04
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200 mW-class LED-based optical wireless power transmission for compact IoT
摘要： For Internet of Things terminals such as many types of sensors, tags or beacons, wiring and using batteries are less effective power supplying methods due to excessive installation and maintenance costs. Wireless power transmission is a promising candidate, particularly optical wireless power transmission (OWPT), with its attractive advantages of long transmission distance, good directionality and small size. However, previous researches of OWPT are almost all focused on laser as a light source, which is difficult to use in the usual spaces due to possible safety reasons at the current stage. In this research, an LED-based OWPT system that realized large electricity power supply was designed and demonstrated. 223.9 mW of output power from 100 cm distance was achieved with a 1.7 × 1.7 cm2 size GaAs solar cell as a receiver. Around 77% of optical system efficiency was confirmed at a 2.1 × 2.3 cm2 irradiation size. The total power feeding efficiency was 6.3%.
关键词： optical wireless power transmission,IoT,LED,GaAs solar cell,wireless power transmission
更新于2025-09-11 14:15:04
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InAs on GaAs Photodetectors Using Thin InAlAs Graded Buffers and Their Application to Exceeding Short-Wave Infrared Imaging at 300?K
摘要： Short-wave infrared (SWIR) detectors and emitters have a high potential value in several fields of applications, including the internet of things (IoT) and advanced driver assistance systems (ADAS), gas sensing. Indium Gallium Arsenide (InGaAs) photodetectors are widely used in the SWIR region of 1–3 μm; however, they only capture a part of the region due to a cut-off wavelength of 1.7 μm. This study presents an InAs p-i-n photodetector grown on a GaAs substrate (001) by inserting 730-nm thick inxAl1?xAs graded and AlAs buffer layers between the InAs layer and the GaAs substrate. At room temperature, the fabricated InAs photodetector operated in an infrared range of approximately 1.5–4 μm and its detectivity (D*) was 1.65 × 108 cm · Hz1/2 · W?1 at 3.3 μm. To demonstrate performance, the Sherlock Holmes mapping images were obtained using the photodetector at room temperature.
关键词： InxAl1?xAs graded buffer,InAs p-i-n photodetector,GaAs substrate,room temperature operation,Short-wave infrared (SWIR),InGaAs photodetectors
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) - A 12.6 – 15 μm Mid-IR Source Based on Difference Frequency Generation in Orientation-Patterned GaAs
摘要： Tunable laser sources in the mid-infrared (mid-IR) spectral range have been of great interest for a variety of applications such as molecular spectroscopy and trace gas detection. Difference-frequency generation (DFG) based on nonlinear frequency conversion in nonlinear crystals has been an effective approach to realize tunable mid-IR laser sources [1]. Among nonlinear crystals, orientation-patterned (OP) GaAs has been highly attractive for mid-IR DFG laser sources due to its large nonlinear susceptibility, lack of birefringence, wide transparency range (0.9 – 17 μm), high thermal conductivity, and high laser-damage-threshold [2,3]. Here, we report the generation of broadly tunable mid-IR radiation across 12.65 – 15 μm based on the DFG approach using an OP-GaAs crystal.
关键词： mid-IR,difference-frequency generation,orientation-patterned GaAs,tunable laser sources,molecular spectroscopy,trace gas detection
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) - Strong Enhancement of Light Extraction Efficiency in Sub-Wavelength AlGaAs/GaAs Vertical-Emitting Nanopillars
摘要： Scaling down active nanophotonic devices, namely nano-lasers and nano-light-emitting diodes (nanoLEDs), to deep sub-micrometer sizes, is crucial to achieve small footprint (<1 μm2), low energy consumption (<10 fJ/bit), and efficient (>10%) light sources, as needed for future compact photonic integrated circuits for optical communications [1], and biosensing and bioimaging applications [2]. As the surface-to-volume ratio of these nanoscale sources increases substantially, among the numerous challenges, strong non-radiative processes and difficulties in extracting the light have been shown to have a detrimental effect on the external quantum efficiencies of nanoLEDs and nanolasers [3]. Although there has been intense research, particularly in light-enhancement and out-coupling methods, using for example 2D photonic crystals [4], optical nanoantennas [5], or nanowaveguides integrated with grating couplers [3], these approaches are extremely challenging to implement when the size of the light-emitting structures is drastically reduced to the deep-subwavelength (<<λ/3) scale. In this work, we report a strong enhanced signal at λ~670 nm in vertical-emitting undoped AlGaAs/GaAs/AlGaAs tapered pillars in a GaAs substrate, Fig. 1(a), when the emitting nominal area is decreased to the sub-μm scale. Vertical-emitting pillars ranging from 200 nm to 8 μm lateral width were fabricated using e-beam lithography and dry etching techniques and characterized using a micro-photoluminescence (PL) microscope with λ=561 nm laser excitation. Figure 1(b) shows examples of emission images for both optically pumped micropillars (top) and nanopillars (bottom) (the respective intensity profiles are shown inset). For the case of micropillars, clearly the light emission is reduced as the diameter decreases following a typical scaling law, d 2, of planar LEDs. However, as d is reduced from 4 μm to 0.2 μm sizes, particularly in the range of 300 nm < d < 400 nm, although the nominal emission area is reduced by a factor of more than 100, the intensity is reduced only by ~10 times. For example, the emitting intensity peaks for pillars with d=360 nm, and the integrated intensity is comparable to pillars with d~1 μm sizes. This strongly deviates from the d 2 dependence observed for micropillars, resulting in a 27-fold enhancement of emission. This striking effect is summarized in Fig. 1(c). Our FDTD simulations for a tapered d=360 nm nanopillar, Fig. 1(a)(bottom), indicate this enhancement is a result of a 3-fold effect: i) suppression of optical modes due to lateral size reduction, ii) efficient out-coupling to air, and iii) more directed emission of tapered pillars. Notably, as shown in the blue circles of Fig. 1(c), the emission can be further improved after surface passivation with (NH4)2S and dielectric capping with a ~50 nm SiO2 layer. For the case of sub-μm pillars, a 3-fold improvement of light emission is achieved as compared with unpassivated samples. In summary, a large improvement of light-extraction in sub-λ vertical-emitting nanopillars is achieved. This pronounced effect enables bright emission in nanoscale devices comparable to the performance of μm-sized devices. This result, combined with the suppression of surface recombination, is crucial for the future development of high-performance nanoscale optoelectronic devices for low-power optical interconnects, supporting the realization of room-temperature highly efficient light sources in photonic integrated circuits.
关键词： sub-wavelength,nanophotonics,vertical-emitting nanopillars,AlGaAs/GaAs,light extraction efficiency
更新于2025-09-11 14:15:04
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Terahertz emission from a weakly-coupled GaAs/AlGaAs superlattice biased into three different modes of current self-oscillations
摘要： Radio-frequency modulated terahertz (THz) emission power from weakly-coupled GaAs/AlGaAs superlattice (SL) has been increased by parallel connection of several SL mesas. Each SL mesa is a self-oscillator with its own oscillation frequency and mode. In coupled non-identical SL mesas biased at different voltages within the hysteresis loop the chaotic, quasiperiodic and frequency-locked modes of self-oscillations of current arise. THz emission was detected when three connected in parallel SL mesas were biased into the frequency-locked and quasiperiodic modes of self-oscillations of current, while in the chaotic mode of those it falls to the noise level.
关键词： current self-oscillations,quasiperiodic mode,terahertz emission,frequency-locked mode,GaAs/AlGaAs superlattice,chaotic mode
更新于2025-09-11 14:15:04
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Two-Color Photodetector for the Visible Spectral Range Based on ZnSe/ZnS/GaAs Bragg Reflector
摘要： Effect of the ZnSe/ZnS/GaAs distributed Bragg reflector (DBR) on the parameters of the spectral response of a photodiode based on rectifying contacts in the metal–semiconductor–metal (MSM) system is studied. The calculated photoreflection spectra of the ZnSe/ZnS/GaAs heterostructure are in good agreement with the experimental data. It is shown that the MSM diode provides two-color response of the photodetector at wavelengths of 420 and 472 nm, a sharp decrease in the photosensitivity in the long-wavelength part of the response signal, high quantum efficiency (53%), and low dark current (5 × 10–10 A). It is demonstrated that the narrow-band two-color response of the detector can be tuned to the desired wavelength using appropriate selection of the parameters of the heterostructure that forms that Bragg reflector.
关键词： two-color photodetector,quantum efficiency,MSM diode,distributed Bragg reflector,ZnSe/ZnS/GaAs
更新于2025-09-11 14:15:04