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Buried defects induced by plasma assisted molecular beam epitaxy of AlN and GaN on Silicon
摘要： The present work is dedicated to the study of peculiar defects observed in GaN/AlN structures grown on Silicon substrate using the plasma assisted Molecular Beam Epitaxy under metal-rich conditions. Optical microscopy shows that these defects have unde?ned shape when AlN is grown on Silicon. On the contrary such defects are not observed with AlN ?lms grown under nitrogen-rich plasma assisted or ammonia source Molecular Beam Epitaxy, but triangular shape defects appear in case of GaN regrowth on the latter. As scanning electron microscopy is not able to evidence these defects but only protuberances connected with them, we deduce that they are located in the Silicon substrate. Complementary analysis with atomic force microscopy and energy dispersive X-ray analysis lead us to propose a scenario involving the etching of the Silicon substrate with Ga or Al di?using through weak points in the nucleation layer.
关键词： A1. Defects,B1. Nitrides on Silicon,A3. Molecular beam epitaxy,B2. Semiconducting materials
更新于2025-09-23 15:21:21
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Graphene-assisted molecular beam epitaxy of AlN for AlGaN deep-ultraviolet light-emitting diodes
摘要： We report on the van der Waals epitaxy of high-quality single-crystalline AlN and the demonstration of AlGaN tunnel junction deep-ultraviolet light-emitting diodes directly on graphene, which were achieved by using plasma-assisted molecular beam epitaxy. It is observed that the substrate/template beneath graphene plays a critical role in governing the initial AlN nucleation. In situ reflection high energy electron diffraction and detailed scanning transmission electron microscopy studies confirm the epitaxial registry of the AlN epilayer with the underlying template. Detailed studies further suggest that the large-scale parallel epitaxial relationship for the AlN epilayer grown on graphene with the underlying template is driven by the strong surface electrostatic potential of AlN. The realization of high-quality AlN by van der Waals epitaxy is further confirmed through the demonstration of AlGaN deep-ultraviolet light-emitting diodes operating at 260 nm, which exhibit a maximum external quantum efficiency of 4% for an unpackaged device. This work provides a viable path for the van der Waals epitaxy of ultra-wide bandgap semiconductors, providing a path to achieve high performance deep-ultraviolet photonic and optoelectronic devices that were previously difficult.
关键词： AlGaN,AlN,molecular beam epitaxy,deep-ultraviolet,light-emitting diodes,van der Waals epitaxy
更新于2025-09-23 15:21:01
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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) - Narrow Bandgap Dilute Nitride Materials for 6-junction Space Solar Cells
摘要： Narrow bandgap p-i-n dilute nitride GaInNAsSb junctions, for use as bottom cell in 6-junction solar cells, are reported. In particular, we demonstrate a high optical quality for GaInNAsSb junction with a bandgap ~0.78 eV, corresponding to a N content of 6.2%. Under AM0 illumination, such cell exhibits a photocurrent of 36.6 mA/cm2. By extracting the parameters of the experimental cell, we estimate the the AM0 efficiency of a 6-junction multijunction solar cell employing the GaInNAsSb junction, to attain a value of 33%. Further improvements are discussed towards achieving the full potential of the 6-junction design.
关键词： GaInNAsSb,dilute nitride,molecular beam epitaxy,multijunction solar cell
更新于2025-09-23 15:21:01
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Molecular beam homoepitaxy on bulk AlN enabled by aluminum-assisted surface cleaning
摘要： We compare the effectiveness of in situ thermal cleaning with that of Al-assisted cleaning of native surface oxides of bulk AlN for homoepitaxial growth by molecular beam epitaxy. Thermal deoxidation performed at 1450 (cid:2)C in vacuum results in voids in the AlN substrate. On the other hand, Al-assisted deoxidation at (cid:3)900(cid:2)C results in high-quality AlN homoepitaxy, evidenced by clean and wide atomic terraces on the surface and no extended defects at the growth interface. This study shows that Al-assisted in situ deoxidation is effective in removing native oxides on AlN, providing a clean surface to enable homoepitaxial growth of AlN and its heterostructures; furthermore, it is more attractive over thermal deoxidation, which needs to be conducted at much higher temperatures due to the strong bonding strength of native oxides on AlN.
关键词： surface cleaning,homoepitaxy,molecular beam epitaxy,aluminum-assisted cleaning,AlN
更新于2025-09-23 15:21:01
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Development and Study of the pa??ia??n GaAs/AlGaAs Tunnel Diodes for Multijunction Converters of High-Power Laser Radiation
摘要： The creation of connecting tunnel diodes with a peak tunneling-current density higher than the density of the short-circuit current of photoactive p–n junctions is an important task in the development of multijunction photoconverters (III–V) of high-power optical radiation. Basing on numerical simulation of the J–U characteristics of tunnel diodes, a method is proposed for increasing the peak tunneling-current density by including a thin undoped i-type layer with a thickness of several nanometers between degenerate layers of the tunnel diode. The p–i–n-GaAs/Al0.2Ga0.8As structures of the connecting tunnel diodes with a peak tunneling-current density of up to 200 A/cm2 are grown by molecular-beam epitaxy.
关键词： quantum tunneling,molecular-beam epitaxy,tunnel diode,multijunction photoconverter,current–voltage characteristic
更新于2025-09-23 15:21:01
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AlInSb/InSb Heterostructures for IR Photodetectors Grown by Molecular-Beam Epitaxy
摘要： A photodetector heterostructure based on AlInSb/InSb was grown by molecular-beam epitaxy. Mesostructures of different diameters were fabricated. The temperature dependence of the dark current was measured. It was demonstrated that the built-in barrier blocks the flow of majority charge carriers, thus reducing the dark-current density (relative to that for a pin structure based on InSb). The measured dependence of the dark current on the mesostructure size revealed that the bulk current component prevails over the surface one.
关键词： nBn detector,molecular-beam epitaxy,dark current,InSb,IR photodetector
更新于2025-09-23 15:21:01
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Epitaxial growth of ultraflat stanene with topological band inversion
摘要： Two-dimensional (2D) topological materials, including quantum spin/anomalous Hall insulators, have attracted intense research efforts owing to their promise for applications ranging from low-power electronics and high-performance thermoelectrics to fault-tolerant quantum computation. One key challenge is to fabricate topological materials with a large energy gap for room-temperature use. Stanene—the tin counterpart of graphene—is a promising material candidate distinguished by its tunable topological states and sizeable bandgap. Recent experiments have successfully fabricated stanene, but none of them have yet observed topological states. Here we demonstrate the growth of high-quality stanene on Cu(111) by low-temperature molecular beam epitaxy. Importantly, we discovered an unusually ultraflat stanene showing an in-plane s–p band inversion together with a spin–orbit-coupling-induced topological gap (~0.3 eV) at the Γ point, which represents a foremost group-IV ultraflat graphene-like material displaying topological features in experiment. The finding of ultraflat stanene opens opportunities for exploring two-dimensional topological physics and device applications.
关键词： topological band inversion,two-dimensional topological materials,molecular beam epitaxy,ultraflat structure,stanene
更新于2025-09-23 15:21:01
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Hybrid P3HT: PCBM/GaN nanowire/Si cascade heterojunction for photovoltaic application
摘要： Poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are commonly used for the fabrication of organic photovoltaics (OPV). Efficiency limitations of OPVs could be circumvented by incorporation of inorganic nanostructures into organic blends. Again, integration of organic solar cells with well-developed silicon photovoltaic technology is ultimately desirable. In the present work, GaN nanowires with diameters of 25–50 nm and two lengths (200 and 500 nm) have been grown using molecular beam epitaxy technique. Solar-grade monocrystalline silicon wafers were used as substrates for nanowire synthesis. GaN nanostructures were incorporated into P3HT:PCBM photoactive layer in order to facilitate charge transfer between P3HT:PCBM and Si. Samples with and without nanowires were compared. Addition of nanowires led to the improvement in photovoltaic performance. Open circuit voltage has risen by 72% and short circuit current density by 200%. Series resistance has decreased 50 times, and power conversion efficiency has risen 20.7 times. Additional maxima are found in photocurrent spectrum corresponding to carriers being generated near GaN absorption edge. Moreover, external quantum efficiency peaks near GaN absorption edge, indicating transfer channel via the formation of current P3HT/GaN/Si cascade heterojunction. Mechanism explaining source of abovementioned improvement is proposed.
关键词： Molecular beam epitaxy,Energy conversion,P3HT,Solar cells,PCBM,GaN nanowires
更新于2025-09-23 15:21:01
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Ultrathin films of L1 <sub/>0</sub> -MnAl on GaAs (001): A hard magnetic MnAl layer onto a soft Mn-Ga-As-Al interface
摘要： Ferromagnetic MnAl (L10-MnAl phase) ultrathin films with thickness varying from 1 to 5 nm have been epitaxially grown on a GaAs (001) substrate. A coercivity above 8 kOe has been obtained with no need of a buffer layer by tuning the sample preparation and the growth parameters. Surface and interface analysis carried out by in situ characterization techniques (x-ray photoelectron spectroscopy and low energy electron diffraction), available in the molecular beam epitaxy chamber, has shown the formation of a ferromagnetic interface consisting of Mn-Ga-As-Al, which contribution competes with the MnAl alloyed film. The appearance of this interface provides important information to understand the growth mechanism of MnAl-based films reported in the literature.
关键词： x-ray photoelectron spectroscopy,ferromagnetic,GaAs,molecular beam epitaxy,low energy electron diffraction,ultrathin films,L10-MnAl
更新于2025-09-23 15:21:01
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Extreme asymmetry of Néel domain walls in multilayered films of the dilute magnetic semiconductor (Ga,Mn)(As,P)
摘要： We report on unconventional perfectly shaped, fully asymmetric ～90? Néel domain walls in multilayered ?lms of the diluted ferromagnetic semiconductor (Ga,Mn)(As,P) with a stepwise variation of P doping. Our results contradict micromagnetic calculations, which favor symmetric domain walls due to crystallographic anisotropy and stray ?eld energy. We demonstrate that both the puzzling uniaxial in-plane anisotropy in the tetragonal multilayered ?lm and the asymmetry of the domain walls could result from Dzyaloshinskii-Moriya interactions that are enhanced by the multiple sharp interfaces between the layers and from anisotropic nonrelativistic exchange coupling. Our ?nding shows that digital variations of composition during the molecular beam epitaxy can be used to tune the anisotropy and chirality of magnetic multilayers.
关键词： diluted magnetic semiconductor,Dzyaloshinskii-Moriya interactions,magnetic anisotropy,Néel domain walls,molecular beam epitaxy
更新于2025-09-23 15:21:01