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Electrical and optical properties of heavily Ge-Doped AlGaN
摘要： We report the effect of germanium as n-type dopant on the electrical and optical properties of AlxGa1-xN layers grown by plasma-assisted molecular-beam epitaxy. The Al content has been varied from x = 0 to 0.66, confirmed by Rutherford backscattering spectrometry, and the Ge concentration was increased up to [Ge] = 1×1021 cm?3. Even at these high doping levels (> 1% atomic fraction) Ge does not induce any structural degradation in AlGaN layers with x < 0.15. However, for higher Al compositions, clustering of Ge forming crystallites were observed. Hall effect measurements show a gradual decrease of the carrier concentration when increasing the Al mole fraction, which is already noticeable in samples with x = 0.24. Samples with x = 0.64-0.66 remain conductive (σ = 0.8-0.3 Ω?1cm?1), but the donor activation rate drops to around 0.1% (carrier concentration around 1×1018 cm?3 for [Ge] ≈ 1×1021 cm?3). From the optical point of view, the low temperature photoluminescence is dominated by the band-to-band emission, which show only spectral shift and broadening associated to the Burstein-Moss effect. The evolution of the photoluminescence peak position with temperature shows that the free carriers due to Ge doping can efficiently screen the potential fluctuations induced by alloy disorder.
关键词： germanium doping,molecular-beam epitaxy,optical properties,AlGaN,electrical properties
更新于2025-09-19 17:15:36
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Molecular beam epitaxy of superconducting PdTe2 films on topological insulator Bi2Te3
摘要： Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insulators. In this study, high-quality superconducting PdTe2 films are deposited on the topological insulator Bi2Te3 surface using molecular beam epitaxy. The surface topography and electronic properties of PdTe2/Bi2Te3 heterostructures are investigated via in situ scanning tunneling microscopy/spectroscopy. Under Te-rich conditions, the Pd atoms presumably form PdTe2 film on Bi2Te3 surface rather than diffuse into Bi2Te3. The superconductivity of the PdTe2/Bi2Te3 heterostructure is detected at a transition temperature of ~1.4 K using the two-coil mutual inductance technique. This study proposes a method for fabricating superconducting materials on topological insulator surfaces at low doping levels, paving ways for designing nanodevices that can manipulate Majorana fermions.
关键词： superconductor,heterostructure,molecular beam epitaxy,topological insulator
更新于2025-09-19 17:15:36
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van der Waals Epitaxy of Earth-Abundant Zn <sub/>3</sub> P <sub/>2</sub> on Graphene for Photovoltaics
摘要： Earth-abundant semiconducting materials are a potential solution for large-scale deployment of solar cells at a lower cost. Zinc phosphide (Zn3P2) is one such earth-abundant material with optoelectronic properties suitable for photovoltaics. Herein, we report the van der Waals epitaxy of tetragonal Zn3P2 (α-Zn3P2) on graphene using molecular beam epitaxy (MBE). The growth on graphene progresses by the formation of Zn3P2 triangular flakes, which merge to form a thin film with a strong (101) crystallographic texture. Photoluminescence (PL) from the Zn3P2 thin films is consistent with previously reported Zn3P2. This work demonstrates that the need of a lattice-matched substrate can be circumvented by the use of graphene as a substrate. Moreover, the synthesis of high-quality Zn3P2 flakes and films on graphene brings new material choices for low-cost photovoltaic applications.
关键词： Zn3P2,graphene,molecular beam epitaxy,photovoltaics,Van der Waals epitaxy
更新于2025-09-19 17:13:59
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Ge <sub/>x</sub> Si <sub/>1-x</sub> Virtual-Layer Enhanced Ferromagnetism in Self-assembled Mn <sub/>0.06</sub> Ge <sub/>0.94</sub> Quantum Dots Grown on Si Wafers by Molecular Beam Epitaxy
摘要： The self-assembled Mn0.06Ge0.94 quantum dots (QDs) on Si substrate or GexSi1-x virtual substrate (VS) were grown by molecular beam epitaxy. The GexSi1-x VS of different thicknesses and Ge compositions x were utilized to modulate the ferromagnetic properties of the above QDs. The MnGe QDs on GexSi1-x VS show a significant enhanced-ferromagnetism with a Curie temperature above 220 K. On the basis of the microstructural and magnetization results, the ferromagnetic properties of the QDs on GexSi1-x VS are believed to come from the intrinsic MnGe ferromagnetic phase rather than any intermetallic ferromagnetic compounds of Mn and Ge. At the same time, we found that by increasing Ge composition x of GexSi1-x VS, the ferromagnetism of QDs grown on VS will markedly increase due to the improvements of hole concentration and Ge composition inside the QDs. These results are fundamentally important in the understanding and especially to the realization of high Curie temperature MnGe diluted magnetic semiconductors.
关键词： ferromagnetism,molecular beam epitaxy,diluted magnetic semiconductors,GexSi1-x virtual substrate,MnGe quantum dots
更新于2025-09-19 17:13:59
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Epitaxial growth and determination of the band alignment for NixMg1-xO/MgO interface by laser molecular beam epitaxy
摘要： By laser molecular beam epitaxy, single crystalline NixMg1-xO films have been successfully synthesized on MgO(100) surface. The in situ reflection high-energy electron diffraction patterns show that the induced O2 background gas with at least 1.0 × 10?3 Pa is necessary to the epitaxial growth of NixMg1-xO films. The X-ray diffraction patterns reveal the single-phase growth along (200) direction. The energy band alignment at the interface is investigated by employing in situ X-ray photoelectron spectroscopy. The valence band offsets are determined to be from 1.47 eV to 1.50 eV with the decrease of Ni content (0.39 / 0.35). Furthermore, the work function is evaluated by using in situ ultraviolet photoemission spectroscopy, indicating the values from 4.33 eV to 4.64 eV. This study provides a promising guidance for the solar-blind device design and fabrication.
关键词： Work function,X-ray photoelectron spectroscopy,Band alignment,Ultraviolet photoemission spectroscopy,Laser molecular beam epitaxy
更新于2025-09-19 17:13:59
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Intrinsically p-type cuprous iodide semiconductor for hybrid light-emitting diodes
摘要： Cuprous halides, characterized by a direct wide band-gap and a good lattice matching with Si, is an intrinsic p-type I-VII compound semiconductor. It shows remarkable optoelectronic properties, including a large exciton binding energy at room temperature and a very small piezoelectric coefficient. The major obstacle to its application is the difficulty in growing a single-crystal epitaxial film of cuprous halides. We first demonstrate the single crystal epitaxy of high quality cuprous iodide (CuI) film grown on Si and sapphire substrates by molecular beam epitaxy. enhanced photoluminescence on the order of magnitude larger than that of GaN and continuous-wave optically pumped lasing were found in MBE grown CuI film. The intrinsic p-type characteristics of CuI were confirmed using an n-AlGaN/p-CuI junction that emits blue light. The discovery will provide an alternative way towards highly efficient optoelectronic devices compatible with both Si and III-nitride technologies.
关键词： molecular beam epitaxy,p-type semiconductor,light-emitting diodes,optoelectronic devices,cuprous iodide
更新于2025-09-19 17:13:59
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Spin excitations in laser-molecular-beam epitaxy grown nanosized YIG films: towards low relaxation and desirable magnetization profile
摘要： We describe synthesis of nanosized Y3Fe5O12 (YIG) films grown by laser-molecular-beam epitaxy on Gd3Ga5O12 (GGG) and Nd3Ga5O12 (NdGG) substrates with (111) orientation and present results of ferromagnetic resonance (FMR) and spin wave propagation studies in these heterostructures. It is found that magnetic parameters of YIG films grown on NdGG and GGG substrates are considerably different. FMR spectra of YIG/NdGG structures are characterized by a large number of narrow peaks, while FMR spectra of YIG/GGG structures consist of a small number of peaks or one peak. The effective magnetization of YIG films grown on NdGG substrates is less than that of YIG films grown on GGG and is more sensitive to the growth conditions. A lateral inhomogeneity of YIG/NdGG structures is observed in spin wave propagation experiments. For YIG/NdGG and YIG/GGG structures the FMR linewidth ?H of a single peak sharply increases with temperature decrease from 298 to 67 K. The observed increase of ?H is explained by typical relaxation processes caused by the presence of Fe2+ ions. From the spin-wave propagation study it is also found that relaxation of spin-waves explains only a minor part of the FMR single peak linewidth in YIG/NdGG structures. On the basis of obtained results, YIG/GGG/semiconductor- and YIG/NdGG/semiconductor-heterostructures with expected low spin-wave relaxation and desirable effective magnetization profile are proposed.
关键词： magnetization profile,ferromagnetic resonance,spin wave propagation,laser-molecular-beam epitaxy,YIG films
更新于2025-09-19 17:13:59
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Photodetectors with 384 × 288 Matrix Elements for the Infrared Range of 8–10 Microns
摘要： Design and fabrication of photosensitive array elements in the 384 × 288 element format with a step of 25 μ m with a long wavelength limit of sensitivity at 0.5 to approximately 9.5 μ m were performed. The circuit and topology were developed, according to which matrix high-speed multiplexers are manufactured in the form of 384 × 288 elements with a step of 25 microns, which provide operating modes at a clock frequency of up to 20 MHz. The 384 × 288 element hybrid photodetector (PD) format in 25 μ m increments has an average Noise Equivalent Temperature Difference (NETD) of less than 30 mK, while the number of working elements was more than 97%. Examples are given of using the microscanning system to reduce defective pixels in an image frame and/or increase the frame format to 768 × 576. It is shown that as a result of the use of microscans in a thermal imaging channel based on the developed PD during the transition to the 768 × 576 format, an improvement in spatial resolution of 1.4 times was obtained for the same minimum resolved temperature difference (MRTD), while the MRTD at a frequency of 0.44 mrad-1 decreased from 1.6 to 0.9 K compared to the original 384 × 288 format.
关键词： MRTD,topology,microscanning,CMT,frame rate,spatial resolution,molecular beam epitaxy,format,PD,NETD,PHE
更新于2025-09-19 17:13:59
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Quantum Dot
摘要： Valley splitting is a key feature of silicon-based spin qubits. Quantum dots in Si/SixGe1?x heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. Here, we demonstrate a robust and large valley splitting exceeding 200 μeV in a gate-defined single quantum dot, hosted in molecular-beam-epitaxy-grown 28Si/SixGe1?x. The valley splitting is monotonically and reproducibly tunable up to 15% by gate voltages, originating from a 6-nm lateral displacement of the quantum dot. We observe static spin relaxation times T1 > 1 s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, T1 is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking.
关键词： valley splitting,spin relaxation,spin qubits,molecular-beam-epitaxy,silicon,quantum dot
更新于2025-09-19 17:13:59
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Growth of InGaAs Solar Cells on InP(001) Miscut Substrates Using Solid‐Source Molecular Beam Epitaxy
摘要： Herein, the effects of both the growth temperature and the substrate miscut on the properties of lattice-matched InGaAs solar cells grown on InP substrates via solid-source molecular beam epitaxy are investigated. The growth temperature is varied from 420 to 490 (cid:1)C. InP(001) miscut by 2(cid:1) toward (111)A and (111)B denoted by 2(cid:1)A and 2(cid:1)B, respectively, and exactly-cut substrates are used. Material quality is evaluated by photoluminescence (PL) and atomic force microscopy (AFM) measurements. At room temperature, the PL emissions become more intense at higher growth temperatures and with miscut substrates, indicating less nonradiative recombination. AFM results show a streaky surface with step structures along the ?1ˉ10(cid:4) direction for cell grown at 490 (cid:1)C on 2(cid:1)A, suggesting that the substrate promotes step-?ow growth. Consequently, the highest conversion ef?ciency (12.3%) for the cell grown at 490 (cid:1)C on 2(cid:1)A is obtained. Especially, the open-circuit voltage (VOC) increases from the baseline of 0.350 V (for the cell grown at 420 (cid:1)C on an exact substrate) to 0.374 V. The Eg(cid:3)VOC de?cit, where W oc, of 369 mV is obtained, which is a standard benchmark for high-material-quality solar cells.
关键词： III–V semiconductors,molecular beam epitaxy,solar cells
更新于2025-09-19 17:13:59