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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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Internal quantum efficiencies of AlGaN quantum dots grown by molecular beam epitaxy and emitting in the UVA to UVC ranges
摘要： AlyGa1?yN quantum dots (QDs) have been grown by molecular beam epitaxy on AlxGa1?xN (0001) using a 2-dimensional–3-dimensional growth mode transition that leads to the formation of QDs. QDs have been grown for Al compositions y varying between 10% and 40%. The influence of the active region design [composition y, QD height, and bandgap difference (ΔEg) between the AlxGa1?xN cladding layer and the AlyGa1?yN QDs] is discussed based on microscopy, continuous wave photoluminescence (PL), and time-resolved PL (TRPL) measurements. In particular, increasing y leads to a shift of the QD emission toward shorter wavelengths, allowing covering a spectral range in the UV from 332 nm (UVA) to 276 nm (UVC) at room temperature (RT). The low-temperature (LT) internal quantum efficiency of the QD ensembles was estimated from TRPL experiments at 8 K and values between 11% and 66% were deduced. The highest internal quantum efficiency (IQE)-LT is found for the QDs with higher Al content y. Then, the PL spectrally integrated intensity ratios between RT and LT were measured to estimate the IQE of the samples at RT. The PL ratio is higher for larger ΔEg, for QDs with y of 0.1 or 0.2, and high PL intensity ratios up to 30% were also measured for QDs with larger y of 0.3 and 0.4. RT IQE values between 5% and 20% are deduced for AlyGa1?yN QDs emitting in the 276–308 nm range.
关键词： AlGaN,internal quantum efficiency,UVC,quantum dots,molecular beam epitaxy,time-resolved photoluminescence,photoluminescence,UVA
更新于2025-09-12 10:27:22
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Growth Habits of Bismuth Selenide (Bi2Se3) layers and nanowires over Stranski–Krastanov Indium Arsenide Quantum Dots
摘要： Bismuth selenide layers and nanowires have been grown by molecular beam epitaxy on self-assembled Stranski–Krastanov InAs quantum dots of different sizes and densities on GaAs substrates. The size and density of the InAs quantum dots were modified by changes in the growth rate and composition. The structure and growth habits of the Bi2Se3 layers were studied by high-resolution x-ray diffraction, scanning probe microscopy, energy-dispersive x-ray spectroscopy and high-resolution electron microscopy. The epitaxial growth of continuous layers of (0001) Bi2Se3 was observed over flat InAs surfaces. In contrast, the presence of InAs quantum dots induced the growth of 100 nm-long and 20 nm-wide Bi2Se3 nanowires primarily oriented along [01-1] and [0-1-1] directions. The nanowires coalesced into full layers when the growth proceeded further. Better understanding and control of the Bi2Se3 growth habits over these surfaces should lead to novel nanostructures with enhanced physical properties.
关键词： InAs quantum dots,Bi2Se3,nanowires,topological insulator,Bismuth selenide,molecular beam epitaxy
更新于2025-09-12 10:27:22
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High‐Purity Triggered Single‐Photon Emission from Symmetric Single InAs/InP Quantum Dots around the Telecom C‐Band Window
摘要： The authors demonstrate pure triggered single-photon emission from quantum dots (QDs) around the telecommunication C-band window, with characteristics preserved under non-resonant excitation at saturation, that is, the highest possible, lifetime-limited emission rates. The direct measurement of emission dynamics reveals photoluminescence decay times in the range of (1.7–1.8) ns corresponding to maximal photon generation rates exceeding 0.5 GHz. The measurements of the second-order correlation function exhibit, for the best case, a lack of coincidences at zero time delay—no multiple photon events are registered within the experimental accuracy. This is achieved by exploiting a new class of low-density and in-plane symmetric InAs/InP QDs grown by molecular beam epitaxy on a distributed Bragg reflector, perfectly suitable for non-classical light generation for quantum optics experiments and quantum-secured fiber-based optical communication schemes.
关键词： spectroscopy,single-photon emission,telecom-wavelength,quantum dots,molecular beam epitaxy
更新于2025-09-12 10:27:22
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[IEEE 2019 European Space Power Conference (ESPC) - Juan-les-Pins, France (2019.9.30-2019.10.4)] 2019 European Space Power Conference (ESPC) - High Efficiency Lattice-Matched 4J Space Solar Cells on GaAs
摘要： A lattice-matched four-junction solar cell on a GaAs substrate, for space applications, is demonstrated. The solar cell incorporates MBE grown GaInP, GaAs, GaInNAsSb and GaInNAsSb junctions with band-gaps of 1.9 eV, 1.4 eV, 1.2 eV and 0.9 eV, respectively. For AM0 illumination, the cell exhibited a maximum efficiency of 27%. For this performance, a high collection efficiency for the bottom cell is required. The high efficiency and current generation for the four-junction solar cell is primarily enabled by achieving a very low background doping level (~5×1014 cm-3) and high charge carrier lifetimes (2-4 ns) for the GaInNAsSb bottom junction. Achieving an efficiency of 33% is deemed possible by further reduction of reflection, shadowing and transmission losses.
关键词： four-junction solar cell,dilute nitrides,molecular beam epitaxy
更新于2025-09-12 10:27:22
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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) - Optoelectronic Devices Based on ZnO/ZnMgO
摘要： The terahertz (THz, 30 μm – 300 μm) spectral region covers various relevant and significant real-world applications like spectral imaging [1], medical diagnostics [2] and trace gas spectroscopy [3]. But due to the lack of high-performance laser sources, it is also referred to as the “THz-gap” in the electromagnetic spectrum. To close this gap, room temperature THz emitting laser sources are needed. Up to now, GaAs-based quantum cascade lasers (QCLs) [4] are the most promising candidates to fulfil this task but they lack significant improvements within recent years concerning their maximum operating temperature and are still limited to operation at cryogenic temperatures around 200K. They are fundamentally limited by the parasitic, non-optical LO-phonon transitions (36meV in GaAs), being on the same order as the thermal energy at room temperature (kT = 26meV). Therefore, other semiconductor materials might solve this problem, including new material systems like ZnO or GaN with their larger LO-phonon energy (ELO,ZnO = 72meV, ELO,GaN = 91meV). While GaN has recently already been investigated in detail without final breakthrough concerning GaN-based QC devices, ZnO is new to this field of application. Consequently, the design and fabrication of ZnO-based QC structures has to be mastered, including a high quality epitaxial growth and well-controlled fabrication processing.
关键词： ZnMgO,quantum cascade lasers,ZnO,molecular beam epitaxy,terahertz
更新于2025-09-12 10:27:22
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Influence of MBE growth parameters on GaSb/GaAs quantum dot morphology
摘要： In this paper, growth of self-assembled type-II GaSb/GaAs quantum dots by molecular beam epitaxy technique is presented. The effect of various growth parameters such as substrate temperature, Sb/Ga beam equivalent pressure ratio, growth rate and total mono-layer coverage on surface morphology is analyzed. The GaSb quantum dots exhibit high anisotropy along <110> and <1-10> directions under specific growth conditions. The anisotropy is discussed on the basis of incorporation of background Arsenic and anisotropic diffusion of Gallium adatoms on the GaSb surface. The low temperature photoluminescence measurements in GaAs capped samples show recombination in the type-II quantum dots and the wetting layer.
关键词： Self assembled process,Anisotropy,Molecular beam epitaxy,Type-II quantum dots,Stranski-Krastanov growth
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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Magnetization reversal in NiFe <sub/>2</sub> O4/SrTiO <sub/>3</sub> nanoheterostructures grown by laser molecular beam epitaxy
摘要： NiFe2O4/SrTiO3(001) nanoheterostructures have been fabricated by laser molecular beam epitaxy method. Surface morphology and crystal structure of Ni-ferrite films were analysed by atomic force microscopy (AFM), reflection of high energy electron diffraction (RHEED), X-ray diffraction (XRD). X-ray methods prove the presence of inverse spinel crystal structure of films that was confirmed by measurements of spectral dependence of optical polar Kerr (PMOKE) effect. Study of magnetization reversal for different orientations of magnetic field carried out by vibration sample magnetometry (VSM) and longitudinal magneto-optical Kerr effect (LMOKE) are presented. In-plane magnetization loops exhibit 90 period indicating presence of biaxial magnetic anisotropy. Asymmetry of LMOKE hysteresis loops is related to manifestation of quadratic in magnetization effects in reflection of light.
关键词： nanoheterostructures,NiFe2O4/SrTiO3,biaxial magnetic anisotropy,laser molecular beam epitaxy,magnetization reversal
更新于2025-09-12 10:27:22
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Emission at 1.6?μm from InAs Quantum Dots in Metamorphic InGaAs Matrix
摘要： Growth of InAs quantum dots (QDs) in metamorphic InGaAs matrix for long-wavelength laser applications on GaAs substrates by molecular beam epitaxy (MBE) is demonstrated. Metamorphic InGaAs matrix is based on a five-step graded InGaAs metamorphic buffer layer (MBL) with a final indium composition of about 40%. Reciprocal space mapping for the asymmetrical ((cid:1)2 2 4) and (2 2 4) reflections along the [(cid:1)1 1 0] and [1 1 0] directions shows anisotropic relaxation along these two directions. The metamorphic InGaAs matrix is more relaxed along [(cid:1)1 1 0] direction but nearly fully strained along [1 1 0] direction. InAs QDs are embedded in two InGaAs confining layers with the same indium composition. Emission at 1.6 μm from metamorphic InAs QDs and 1.42 μm emission from metamorphic InGaAs matrix at room temperature (RT) are observed, respectively. The activation energy of (cid:3)94.6 meV is obtained.
关键词： InAs,metamorphic InGaAs matrix,quantum dots,molecular beam epitaxy,reciprocal space mapping
更新于2025-09-11 14:15:04