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Ferroelectric Enhanced Performance of a GeSn/Ge Dual-Nanowire Photodetector
摘要： GeSn offers a reduced bandgap than Ge and has been utilized in Si-based infrared photodetectors with extended cutoff wavelength. However, traditional GeSn/Ge heterostructure usually consists defects like misfit dislocations due to the lattice mismatch issue. The defects with the large feature size of photodetector fabricated on bulk GeSn/Ge heterostructure induces considerable dark current. Here, we demonstrate a flexible GeSn/Ge dual-nanowire (NW) structure, in which the strain relaxation is achieved by the elastic deformation without introducing defects and the feature dimension is naturally at nanoscale. Photodetector with low dark current can be built on GeSn/Ge dual-NW, which exhibits an extended detection wavelength beyond 2 μm and the enhanced responsivity compared to Ge NW. Moreover, the dark current can be further suppressed by the depletion effect from ferroelectric polymer side gate. Our work suggests the flexible GeSn/Ge dual-NW may open an avenue for Si-compatible optoelectronic circuits operating in the short-wavelength infrared range.
关键词： Nanowire,Germanium-tin,Molecular beam epitaxy (MBE),Side-gated,Photodetector,Ferroelectrical polymer
更新于2025-11-21 11:01:37
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Optimised Performance of Non-Dispersive Infrared Gas Sensors Using Multilayer Thin Film Bandpass Filters
摘要： In this work, performance improvements are described for a low-power consumption non-dispersive infrared (NDIR) methane (CH4) gas sensor using customised optical thin film bandpass filters (BPFs) centered at 3300 nm. BPFs shape the spectral characteristics of the combined mid-infrared III–V based light emitting diode (LED)/photodiode (PD) light source/detector optopair, enhancing the NDIR CH4 sensor performance. The BPFs, deposited using a novel microwave plasma-assisted pulsed DC sputter deposition process, provide room temperature deposition directly onto the temperature-sensitive PD heterostructure. BPFs comprise germanium (Ge) and niobium pentoxide (Nb2O5) alternating high and low refractive index layers, respectively. Two different optical filter designs are progressed with BPF bandwidths (BWs) of 160 and 300 nm. A comparison of the modelled and measured NDIR sensor performance is described, highlighting the maximised signal-to-noise ratio (SNR) and the minimised cross-talk performance benefits. The BPF spectral stability for various environmental temperature and humidity conditions is demonstrated.
关键词： III–V,sensor,methane,thin film,MBE,NDIR,microwave,bandpass,sputter,heterostructure,infrared
更新于2025-09-23 15:23:52
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Structural and Optical Properties of AlN/GaN and AlN/AlGaN/GaN thin films on Silicon Substrate prepared by Plasma Assisted Molecular Beam Epitaxy (MBE)
摘要： In this study, the Aluminium Nitride/Gallium Nitride (AlN/GaN) layers and Aluminium Nitride/Aluminium Gallium Nitride/Gallium Nitride (AlN/AlGaN/GaN) layer heterostructures were successfully created using technique known as plasma-assisted molecular beam epitaxy (MBE) on silicon substrate. Gallium (7N) and Aluminium (6N5) of high purity were used to grow GaN, AlN and AlGaN respectively. The structural and optical properties of the prepared AlN/GaN and AlN/AlGaN/GaN layer heterostructures were investigated by means of atomic force microscope (AFM), X-ray diffraction (XRD), photoluminescence spectroscopy (PL) and Raman spectroscopy. AFM measurement demonstrated that the root mean square of surface roughness for AlN/GaN and AlN/AlGaN/GaN heterostructures are 3.677 nm and 10.333 nm respectively. XRD data indicated that the samples have typical diffraction pattern of hexagonal structure. Raman spectra revealed all four Raman-active modes present inside both samples. PL spectra data showed the yellow luminescence which corresponds to the deep energy levels due to imperfections of AlN did not appear. Thus, PL observation indicated that the thin film of AlN/GaN and AlN/AlGaN/GaN layers have good optical quality and looks promising for various target applications in optoelectronics, photovoltaic and radiofrequency applications.
关键词： silicon,thin film,MBE,Aluminium Nitride,Gallium Nitride,Aluminium Gallium Nitride
更新于2025-09-23 15:23:52
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Rare Earth Doping of Topological Insulators: A Brief Review of Thin Film and Heterostructure Systems
摘要： Magnetic topological insulators (MTIs) are a novel materials class in which a topologically nontrivial electronic band structure coexists with long-range ferromagnetic order. The ferromagnetic ground state can break time-reversal symmetry, opening a gap in the topological surface states whose size is dependent on the magnitude of the magnetic moment. Doping with rare earth ions is one way to introduce higher magnetic moments into a material, however, in Bi2Te3 bulk crystals, the solubility limit is only a few percent. Using molecular beam epitaxy for the growth of doped (Sb,Bi)2(Se,Te)3 TI thin films, high doping concentrations can be achieved while preserving their high crystalline quality. The growth, structural, electronic, and magnetic properties of Dy, Ho, and Gd doped TI thin films will be reviewed. Indeed, high magnetic moments can be introduced into the TIs, which are, however, not ferromagnetically ordered. By making use of interfacial effects, magnetic long-range order in Dy doped Bi2Te3, proximity-coupled to the MTI Cr:Sb2Te3, has been achieved. Clearly, engineered MTI heterostructures offer new possibilities that combine the advantageous properties of different layers, and thus provide an ideal materials platform enabling the observation new quantum effects at higher temperatures.
关键词： rare earth doping,MBE,topological insulators,heterostructure,bismuth telluride,antimony telluride
更新于2025-09-23 15:22:29
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Optical Band Gap, Local Work Function and Field Emission Properties of MBE Grown β-MoO3 Nanoribbons
摘要： Monoclinic molybdenum trioxide (β-MoO3) nanostructures (shaped like nanoribbons: NRs) were grown on Si(100), Si(5512) and fluorine-doped tin oxide (FTO) by molecular beam epitaxy (MBE) technique under ultra-high vacuum (UHV) conditions. The dependence of substrate conditions and the effective thickness of MoO3 films on the morphology of nanostructures and their structural aspects were reported. The electron microscopy measurements show that the length and the aspect ratio of nanostructures increased by, 260% without any significant change in the width for a change in effective thickness from 5 nm to 30 nm. NRs are grown along <011> for all the effective thickness of MoO3 films. Similarly, when we increased the film thickness from 5 nm to 30 nm, the optical band gap decreased from 3.38± 0.01eV to 3.17± 0.01eV and the local work function increased from 5.397 ± 0.025 eV to 5.757 ± 0.030 eV. Field emission turn-on field decreased from 3.58 V/μm for 10-μA/cm2 to 2.5 V/μm and field enhancement factor increased from 1.1×104 to 5.9×104 for effective thickness variation of 5 nm to 30 nm β-MoO3 structures. The β-MoO3 nanostructures found to be much better than the α-MoO3 nanostructures due to low work function, low turn on field and high field enhancement factor, and are expected to be useful applications.
关键词： β-MoO3 nanostructures,Field emission and Kelvin probe force microscopy (KPFM),Optical band gap,Molecular beam epitaxy (MBE),Electron microscopy
更新于2025-09-23 15:22:29
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Microscopy and Spectroscopy Study of Nanostructural Phase Transformation from β-MoO3 to Mo under UHV – MBE Conditions
摘要： We report a simple reduction of molybdenum oxide (β-MoO3) grown on reconstructed Si(100) by thermal annealing in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). By increasing the substrate temperature during deposition or the annealing temperature after growth, the morphologies of as-deposited structures were found to vary from nanoribbons (NRs) of β-MoO3 to nanoparticles (NPs) of Mo. The change in morphologies have been associated with a structural transition from β-MoO3 to MoO2 at 400 °C and MoO2 to Mo at 750 °C. The in-situ X-ray photoelectron spectroscopy (XPS) measurements revealed a shift of the Mo 3d peaks towards lower binding energies, representing the reduction in Mo oxidation states until a pure Mo 3d peak at 750°C was observed. The ex-situ KPFM measurements showed a decrease in the local work function (Φ) (from ≈ 5.27 ± 0.05 eV to ≈ 4.83 ± 0.05 eV) with increasing substrate temperature. A gradual reduction of the band gap from ≈ 3.32 eV for β-MoO3 NRs to zero band gap for Mo NPs is also observed during the annealing up to 750 °C.
关键词： in-situ XPS,KPFM,molecular beam epitaxy (MBE),Mo nanoparticles,β-MoO3 nanoribbons,phase transition
更新于2025-09-23 15:22:29
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<i>β</i> -Ga <sub/>2</sub> O <sub/>3</sub> thin film grown on sapphire substrate by plasma-assisted molecular beam epitaxy
摘要： Monoclinic gallium oxide (Ga2O3) has been grown on (0001) sapphire (Al2O3) substrate by plasma-assisted molecular beam epitaxy (PA-MBE). The epitaxial relationship has been confirmed to be [010](ˉ201)β-Ga2O3||[1ˉ100](0001)Al2O3 via in-situ reflection high energy electron diffraction (RHEED) monitoring and ex-situ X-ray diffraction (XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum (FWHM) of XRD ω-rocking curve of (ˉ201) plane and root mean square (RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C, respectively. Room temperature cathodoluminescence measurement shows an emission at ~417 nm, which is most likely originated from recombination of donor–acceptor pair (DAP).
关键词： CL measurement,β-Ga2O3,sapphire substrate,PA-MBE,crystalline quality
更新于2025-09-23 15:22:29
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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
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1.73 eV AlGaAs/InGaP heterojunction solar cell grown by MBE with 18.7% efficiency
摘要： We report on AlGaAs-based heterojunction solar cells grown by solid source molecular beam epitaxy (MBE). We investigate InGaP and AlGaAs material quality and we demonstrate significant efficiency improvements by combining the best of each alloy: a thick p-AlGaAs base with tunable bandgap, and a thin 50 nm n-InGaP emitter separated by a thin intrinsic AlGaAs layer. We report a certified solar cell conversion efficiency of 18.7% with a 2-μm-thick AlGaAs layer and a bandgap of 1.73 eV, suitable for high efficiency Si-based tandem devices.
关键词： AlGaAs,MBE,InGaP,III-V solar cells,heterostructure
更新于2025-09-19 17:13:59
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HgCdTe-Based 640 ?? 512 Matrix Midwave Infrared Photodetector
摘要： Matrix photosensitive elements based on a HgCdTe semiconductor solid solution on silicon substrates with 640 × 512 elements at a pitch of 25 μ m with a long-wavelength sensitivity of 5 μ m at half maximum are designed and produced. The scheme and topology are developed according to which matrix multiplexers with 640 × 512 elements at a pitch of 25 μ m, which ensure operating modes at a clock frequency up to 10 MHz, are manufactured. Using a hybrid assembly method on indium bumps, a matrix photodetector with 640 × 512 elements at a pitch of 25 μ m is produced. The best photodetector specimens are characterized by the following parameters: average NETD value <13 mK and the number of workable elements > 99.5%.
关键词： SWaP,MBE,MCT,photodetectors,FPA,NETD
更新于2025-09-19 17:13:59