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- 2018
- differential low noise amplifier
- GaAs pHEMT
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- National Taiwan University
- Academia Sinica
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Single-photon emission from single-electron transport in a SAW-driven lateral light-emitting diode
摘要： The long-distance quantum transfer between electron-spin qubits in semiconductors is important for realising large-scale quantum computing circuits. Electron-spin to photon-polarisation conversion is a promising technology for achieving free-space or fibre-coupled quantum transfer. In this work, using only regular lithography techniques on a conventional 15 nm GaAs quantum well, we demonstrate acoustically-driven generation of single photons from single electrons, without the need for a self-assembled quantum dot. In this device, a single electron is carried in a potential minimum of a surface acoustic wave (SAW) and is transported to a region of holes to form an exciton. The exciton then decays and creates a single optical photon within 100 ps. This SAW-driven electroluminescence, without optimisation, yields photon antibunching with g(2)(0) = 0.39 ± 0.05 in the single-electron limit (g(2)(0) = 0.63 ± 0.03 in the raw histogram). Our work marks the first step towards electron-to-photon (spin-to-polarisation) qubit conversion for scaleable quantum computing architectures.
关键词： quantum computing,GaAs quantum well,electron-spin qubits,surface acoustic wave,single-photon emission
更新于2025-09-23 15:19:57
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Effects of post bonding annealing on GaAs//Si bonding interfaces and its application for sacrificial-layer-etching based multijunction solar cells
摘要： By using the sacrificial layer (SL) etching, GaAs substrates are separated from III–V epi substrate//Si substrate junctions that are made by surface activated bonding (SAB) technologies. The post-bonding low-temperature (300-?C) annealing plays an essential role in achieving a promising (～90%) bonding yield. The effects of the post-bonding annealing are investigated by hard X-ray photoemission spectroscopy and current–voltage measurements of GaAs//Si bonding interfaces. It is found that the concentration of oxygen atoms at interfaces is reduced and the resistance decreases to 1.6–2.1 m??cm2 by the low-temperature annealing. Aluminum fluoride complexes are not observed by X-ray photoelectron spectroscopy on the exposed surfaces of separated GaAs substrates. The roughness average of the surfaces is ≈0.25–0.30 nm. The characteristics of double junction cells fabricated on the GaAs//Si junctions prepared by the SL etching are almost the same as those of cells fabricated by dissolving GaAs substrates after bonding. These results indicate that multijunction cells could be fabricated in a process sequence compatible with reuse of GaAs substrates by combining the SL etching and SAB.
关键词： Sacrificial layer etching,GaAs//Si double junction cells,Surface activated bonding,Low temperature annealing,Epitaxial lift-off
更新于2025-09-23 15:19:57
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Numerical optimisation and recombination effects on the vertical-tunnel-junction (VTJ) GaAs solar cell up to 10,000 suns
摘要： Ultra-high concentrator photovoltaic systems (UHCPV), usually referred to CPV systems exceeding 1000 suns, are signalled as one of the most promising research avenues to produce a new generation of high-efficiency and low-cost CPV systems. However, the structure of current concentrator solar cells prevents their development due to the unavoidable series resistance losses at such elevated concentration ratios. In this work, we investigate the performance of the so-called vertical-tunnel-junction (VTJ), recently introduced by the authors, by using advance TCAD. In particular, we carry out an optimisation procedure of the key parameters that affect its performance and conduct a deep investigation of the impact of the main recombination mechanisms and of sun concentration up to 10,000 suns. The results indicate that the performance of the novel structure is not significantly affected by these two factors. A record efficiency of 32.2% at 10,000 suns has been found. This represents a promising way to obtain state-of-the-art efficiencies above 30% for single-band-gap cells, and offers a new route towards the development of competitive CPV systems operating at ultra-high concentration fluxes.
关键词： Tunnel diode,Concentrator photovoltaics,Vertical solar cells,Series resistance,Gallium arsenide (GaAs)
更新于2025-09-23 15:19:57
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - A GaAs Integrated Power Divider Based on Microstrip and LC Structure with Optimized Capacitance
摘要： In this paper, a microstrip LC two-section Wilkinson power divider based on GaAs IPD process is proposed. A method on adjusting circuit parameters is demonstrated, which can compensate the parasitic e?ects of frequency-dependent passive components. One of the sections is a lumped LC network and the other section consists of microstrip lines. This design can reduce the size of the power divider and avoid a high loss. The inductance and capacitance of this power divider are calculated to ensure that the LC network is equivalent to a microstrip line. However, the capacitances and inductances are all sensitive to frequency so there is a signi?cant variation among calculation with ideal components and simulation with practical models. To solve this problem, even-mode input admittance is studied. By plotting a polar diagram of ideal and simulated even-mode input admittances, it is clear that a di?erence exists among simulation and ideal target, which causes the performance degeneration. This polar diagram also indicates a method on optimizing the admittance by increasing capacitance in the LC network. Increased capacitances are utilized in power divider simulation. Simulated results are compared and an optimized capacitance, which guides our ?nal design, is obtained. This power divider is fabricated using GaAs IPD process and measured on wafer. Measurement agrees well with simulation: operation band is 2.850 GHz to 4.832 GHz. A 1.982 GHz bandwidth is achieved. The insertion loss of port 2, 3 is less than 1.30 dB in this frequency range, and the isolation is higher than 18.5 dB.
关键词： frequency-dependent passive components,Wilkinson power divider,GaAs IPD process,microstrip LC,even-mode input admittance
更新于2025-09-23 15:19:57
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Giant Stark effect in coupled quantum wells: Analytical model
摘要： Coupled quantum wells have been proposed as candidates for highly polarizable structures due to their near-degenerate and dipole-coupled electronic states. Hence, many interesting applications in linear and nonlinear optics can be envisioned. We analyze this proposal considering a simple structure with a delta-function barrier separating the wells. While very substantial Stark shifts are certainly predicted for this geometry, perturbative estimates based on polarizabilities (and hyperpolarizabilities) fail beyond a critical ?eld strength that depends inversely on the barrier. Hence, a giant Stark effect due to near-degenerate states is invariably limited by a small critical ?eld. Our analytical (hyper) polarizability expressions are applied to ?nd quantitative Stark shifts for GaAs quantum wells and transition-metal dichalcogenide bilayers. The predicted Stark shifts and critical ?elds agree with the ?eld dependence observed in a range of available experiments.
关键词： Stark effect,hyperpolarizability,GaAs,transition-metal dichalcogenide bilayers,polarizability,coupled quantum wells
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) - Wet-Chemically Textured Ultra-Thin GaAs Solar Cells with Dielectric/Metal Rear Mirrors
摘要： The rear-side contact layer of ultra-thin GaAs solar cells was textured using a simple, one-step wet chemical approach. A ZnS/Ag double layer was conformally deposited to function as a diffusive rear mirror. Local Ohmic contact points provided electrical contact directly to the Ag. The textured solar cells were compared with planar reference cells fabricated on the same wafer and a clear enhancement of long-wavelength quantum efficiency and short-circuit current was observed in the textured cells. Both architectures showed FF > 80% and VOC > 1 V. Additionally, the rear-side texture increases the external luminescent efficiency by enhancing outcoupling of luminescence.
关键词： light trapping,ultra-thin GaAs solar cells,dielectric mirror,wet etching
更新于2025-09-23 15:19:57
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Effect of tunnel junction grown at different growth rates on the optical properties and improved efficiency of InGaP/GaAs double-junction solar cells
摘要： The optical properties of InGaP/GaAs double-junction solar cells (DJSCs) grown by metalorganic chemical vapor deposition were investigated using temperature- and excitation power-dependent photoluminescence (PL) measurements. The InGaP/GaAs DJSC samples studied were the same structures; however, the corresponding tunnel junctions were grown at different growth rates (1.0 and 1.5 ?/s). The PL spectrum measured at 10 K for both samples exhibited a strong main peak at ~1.97 eV with a weak shoulder peak at ~1.94 eV, which could be attributed to the emissions of disordered and ordered InGaP, respectively. A PL peak located at ~1.91 eV was observed under a low excitation power, originating from the donoreacceptor pair (DAP) transition. With the increase in the temperature, the emission related to the DAP of the sample grown at a growth rate of 1.0 ?/s was found to be less dominant compared with the sample grown at a growth rate of 1.5 ?/s. The power-conversion ef?ciency of the sample grown at a growth rate of 1.0 ?/s was improved compared to that of the sample grown at a growth rate of 1.5 ?/s, owing to fewer defect states. Our results help understand the luminescence properties of InGaP/GaAs DJSCs, which could be a crucial factor in fabricating high-ef?ciency solar cells.
关键词： InGaP/GaAs,Growth rate,Photoluminescence,Double-junction solar cell
更新于2025-09-23 15:19:57
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1200nma??Band InAs/GaAs Quantum Dot Intermixing by Dry Etching and Ion Implantation
摘要： In this paper, the quantum dot intermixing (QDI) technique previously developed for 1550nm-band InAs/InAlGaAs quantum dot (QD) was applied to 1200nm-band InAs/GaAs QD. Three methods of defect introduction for triggering the QDI were employed such as ICP-RIE (Ar+) and ion implantation (Ar+ and B+). As a result, about 80nm PL peak wavelength shift was obtained for ICP-RIE when annealing was performed at 575 °C, after etching down to 450 nm to the QD layer. On the other hand, about 110nm PL peak wavelength shift was obtained for B+ ion implantation at an acceleration energy of 120 keV and a dose of 1.0×1014 /cm2 and subsequent annealing. Cross sectional image analyses by Scanning Transmission Electron Microscope (STEM) and Energy-Dispersive X-ray Spectroscopy (EDX) clarified the modification of InAs QD structures by the QDI process.
关键词： intermixing,InAs/GaAs quantum dot,ICP-RIE,rapid thermal annealing,ion implantation
更新于2025-09-23 15:19:57
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Photonic Crystal Circular Nanobeam Cavity Laser with Type-II GaSb/GaAs Quantum Rings as Gain Material
摘要： The optical emission from type-II semiconductor nanostructures is influenced by the long carrier lifetime and can exhibit remarkable thermal stability. in this study, utilizing a high quality photonic crystal circular nanobeam cavity with a high quality factor and a sub-micrometer mode volume, we demonstrated an ultra-compact semiconductor laser with type-ii gallium antimonide/gallium arsenide quantum rings (GaSb/GaAs QRs) as the gain medium. the lasing mode localized around the defect region of the nanobeam had a small modal volume and significant coupling with the photons emitted by QRs. it leads the remarkable shortening of carrier lifetime observed from the time-resolved photoluminescence (tRpL) and a high purcell factor. furthermore, a high characteristic temperature of 114 K was observed from the device. The lasing performances indicated the type-II QRs laser is suitable for applications of photonic integrated circuit and bio-detection applications.
关键词： gain material,laser,nanobeam cavity,type-II GaSb/GaAs Quantum Rings,photonic crystal
更新于2025-09-23 15:19:57
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A high throughput, linear molecular beam epitaxy system for reduced cost manufacturing of GaAs photovoltaic cells: will GaAs ever be inexpensive enough?
摘要： Solar cells based on GaAs and related compounds provide the highest reported efficiency single junction and multijunction solar cells. However, the cost of the cells is prohibitive when compared with Si and other thin film solar technologies. One significant differentiator is the high cost required to grow the epitaxial layers. Here, we propose a molecular beam epitaxy (MBE) system design that has the potential to increase the epitaxial layer growth throughput, thereby significantly reducing production costs. A rack-and-pinion based linear transfer system sequentially transfers multiple substrate platens between interconnected growth positions within the chamber, thereby synchronously growing layers on many wafers in the desired order and at the required thicknesses. The proposed linear MBE platform is the basis for a realistic analysis of GaAs single junction photovoltaic cell production cost. Our model projects a nearly 55% cost reduction in epitaxial growth via linear MBE when compared to conventional MBE, and a 85% reduction when further process optimization is assumed and combined with non-destructive lift off. Even when considering all of these factors in an optimistic light, the cost of epitaxial unconcentrated GaAs solar cells using any existing growth process is unlikely to drop below $3 per Wp in the foreseeable future.
关键词： photovoltaic cells,GaAs,molecular beam epitaxy,linear MBE,cost reduction
更新于2025-09-23 15:19:57