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High germanium doping of GaN films by ammonia molecular beam epitaxy
摘要： Doping Gallium nitride (GaN) with elemental Germanium (Ge) grown by ammonia molecular beam epitaxy is presented. Growth studies varying the GaN growth rate, substrate growth temperature and the elemental Ge flux reveal several incorporation dependencies. Ge incorporation increases with flux, as expected, and a doping range from ~1017 cm-3 to 1020 cm-3 was readily achieved. A strong substrate temperature dependence on the electrical properties of films grown is observed, with an optimal growth temperature of 740 °C, lower than standard GaN growth conditions for the ammonia molecular beam epitaxy. Compensation effects at higher growth temperatures are suspected, as observed with other techniques. Crystallographic defects are apparent at the highest doping concentrations from electrical and optical measurements, however thin layers of such highly doped films are of great interest for contact layers and tunnel junctions in devices.
关键词： Ammonia Molecular Beam Epitaxy,Molecular Beam Epitaxy,Tunnel Junctions,Germanium Doping,Gallium Nitride
更新于2025-09-04 15:30:14
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High-efficiency electron-beam-pumped sub-240-nm ultraviolet emitters based on ultra-thin GaN/AlN multiple quantum wells grown by plasma-assisted molecular-beam epitaxy on <i>c</i> -Al <sub/>2</sub> O <sub/>3</sub>
摘要： We report the internal structures and emission properties of GaN/AlN single- and multiple-quantum-well (QW) heterostructures with well widths of dw = 1–4 monolayers (MLs), grown by plasma-assisted molecular-beam epitaxy on c-sapphire at metal-rich conditions and low temperatures (>700 °C). The formation of plane QWs with abrupt symmetrical interfaces is con?rmed by both scanning transmission electron microscopy and X-ray di?raction analysis. Pulse-scanning and continuous-wave output powers of 150 and 28 mW, respectively, at a peak emission wavelength of 235 nm were achieved at 300 K in an electron-beam-pumped deep-ultraviolet (1.5 ML-GaN/5.5 nm-AlN)360 multiple-QW emitter with a maximum e?ciency of 0.75%.
关键词： plasma-assisted molecular-beam epitaxy,electron-beam-pumped,deep-ultraviolet emitters,GaN/AlN,quantum wells
更新于2025-09-04 15:30:14
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Suppression of segregation of the phosphorus δ-doping layer in germanium by incorporation of carbon
摘要： The successful formation of abrupt phosphorus (P) δ-doping profiles in germanium (Ge) is reported. When the P δ-doping layers were grown by molecular beam epitaxy (MBE) directly on Ge wafers whose surfaces had residual carbon impurities, more than a half the phosphorus atoms were confined successfully within a few nm of the initial doping position even after the growth of Ge capping layers on the top. On the other hand, the same P layers grown on Ge buffer layers that had much less carbon showed significantly broadened P concentration profiles. Current–voltage characteristics of Au/Ti/Ge capping/P δ-doping/n-Ge structures having the abrupt P δ-doping layers with carbon assistance showed excellent ohmic behaviors when P doses were higher than 1 × 1014 cm?2 and the capping layer thickness was as thin as 5 nm. Therefore, the insertion of carbon around the P doping layer is a useful way of realizing ultrashallow junctions in Ge.
关键词： germanium,carbon incorporation,molecular beam epitaxy,ohmic contacts,phosphorus δ-doping
更新于2025-09-04 15:30:14
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Spin splitting in EuO(111)/Si(111) spin-filter tunnel junctions with atomically sharp interface
摘要： We demonstrate the tunneling in spin-split barriers made of ferromagnetic EuO grown on Si(111) substrates by molecular beam epitaxy. For 6 nm thick EuO films with high crystal quality and atomically sharp interfaces, we find a barrier height lowering driven by the spin splitting below the Curie temperature of 35 K. We determined the splitting energy to be 0.56 + 0.03 eV at 20 K which results in a spin polarization above 90%.
关键词： molecular beam epitaxy,atomically sharp interface,EuO(111)/Si(111),spin splitting,spin-filter tunnel junctions
更新于2025-09-04 15:30:14
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Molecular beam epitaxy growth of Mn4?Ni N thin films on MgO(0?0?1) substrates and their magnetic properties
摘要： We grew Mn4?xNixN epitaxial thin ?lms on MgO(0 0 1) by molecular beam epitaxy, as well as studied their crystalline qualities and magnetic properties. The ?lms were decomposed into Ni8N or Mn-Ni alloys when x ≥ 2, as con?rmed by X-ray di?raction and re?ection high-energy electron di?raction, but this decomposition was mitigated by reducing the substrate growth temperature. The lattice constants decreased with increased Ni substitution except when the Mn ratio was high, while the crystal orientation tended to degrade. The magnetic properties were measured via vibrating sample magnetometer, and it was found that the saturation magneti- zation (MS) and perpendicular magnetic anisotropy (PMA) diminished with a small amount of Ni substitution. Speci?cally, the MS value was remarkably decreased from 86.3 ± 1.1 emu/cm3 (Mn4N) to 19.0 ± 0.5 emu/cm3 (Mn3.85Ni0.25N), and the magnetic anisotropy constant was decreased from approximately 0.94–0.027 Merg/ cm3, respectively. The PMA vanished with further Ni substitution. Ultimately, a small MS and a PMA were simultaneously achieved with a small amount of Ni substitution. These properties support spin transfer torque, which can be applied to the emerging non-volatile memory devices using domain wall motion.
关键词： A3. Molecular beam epitaxy,A1. Crystal structure,B1. Mn4N,B2. Magnetic materials,B1. MgO,B1. Ni4N
更新于2025-09-04 15:30:14
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Advantage of heteroepitaxial GaSb thin-film buffer and GaSb dot nucleation layer for GaSb/AlGaSb multiple quantum well structure grown on Si(1?0?0) substrate by molecular beam epitaxy
摘要： We grew a GaSb/Al0.3Ga0.7Sb multiple-quantum-well (MQW) structure on a two-inch Si(1 0 0) substrate using a 100-nm-thick heteroepitaxial GaSb thin-film buffer with a nucleation layer of GaSb dots by molecular beam epitaxy (MBE) and evaluated the surface morphology and the photoluminescence (PL) and X-ray diffraction spectra of the MQW structure. The full width at half maximum of the PL spectrum of the GaSb/Al0.3Ga0.7Sb MQW structure was very narrow, although the buffer thickness was much lower than those for previously reported GaSb-based QW structures on Si(1 0 0) substrates. This indicated that the surface of the 100-nm-thick GaSb thin-film buffer was sufficiently flat to form heterostructures and MQWs. The surface roughness and crystalline quality of the GaSb buffer and MQW structure were strongly dependent on the growth temperature; high-performance devices were realized by optimizing the growth temperature. These results showed the advantage and potential applicability of the GaSb/Al0.3Ga0.7Sb MQW structure and the GaSb thin-film buffer with GaSb dots as a nucleation layer grown on Si(1 0 0) substrates.
关键词： A1. Nucleation layer,B1. Gallium antimonide,A3. Quantum wells,B2. Semiconducting III–V materials,A3. Molecular beam epitaxy (MBE),B1. Silicon substrate
更新于2025-09-04 15:30:14
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The Effect of Charge Transport Mechanisms on the Efficiency of AlxGa1 – xAs/GaAs Photodiodes
摘要： Photovoltaic characteristics of heterostructure AlxGa1 – xAs/GaAs p–i–n photodiodes fabricated by molecular-beam epitaxy have been studied. Efficiencies of 50% were reached in conversion of monochromatic light in the photovoltaic mode at power density of up to 200 W/cm2 at a wavelength λ = 830 nm. A relationship was demonstrated between the “saturation currents” for the diffusion-related charge-transport mechanism (Shockley) in p–i–n photodiodes, calculated from dark current–voltage characteristics, and the experimental values of efficiency. As the “saturation current” of the diffusion-related charge-transport mechanism increases by an order of magnitude, a relative decrease in the efficiency from the maximum value by more than 10% is observed under excitation by constant or pulsed monochromatic light.
关键词： efficiency,charge transport mechanisms,molecular-beam epitaxy,photodiodes,AlxGa1 – xAs/GaAs
更新于2025-09-04 15:30:14
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Metamorphic InAs(Sb)/InGaAs/InAlAs nanoheterostructures grown on GaAs for efficient mid-IR emitters
摘要： High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5 μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1 ? are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ～8 μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic InxAl1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded InxAl1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6 μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T = 10–300 K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As4/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3 × 107 cm?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300 nm, the extremely low surface roughness with the RMS value of 1.6–2.4 nm, measured by AFM, as well as rather high 3.5 μm-PL intensity at temperatures up to 300 K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.
关键词： Buffer layer,Non-radiative recombination,Mid-infrared emitters,Photoluminescence,Metamorphic heterostructures,InSb,InAs,Structural properties,Molecular beam epitaxy,Nanostructures,In(Ga,Al)As ternary alloys,Threading dislocations,Quantum well
更新于2025-09-04 15:30:14
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MBE Growth and Optical Properties of Isotopically Purified ZnSe Heterostructures
摘要： Wide-gap II/VI heterostructures (HS) and quantum wells (QW) composed of ZnSe, CdSe, MgSe and their ternary and quaternary compounds are attractive candidates for modern quantum optical devices such as single photon sources and optically controlled spin qubits in the visible spectral range. In contrast to similar III/V semiconductor based devices, generally, most of the II/VI compounds allow for isotope purification towards zero nuclear spin species in the semiconductor environment. Using the same molecular beam epitaxy (MBE) system for natural and isotopically purified materials opposes the challenge to achieve superior isotope purity for example of Zn and Se species on the background of operation of the other effusion cells filled with natural isotopes. Here we report on the crystallographic and optical properties of ZnMgSe/ZnSe heterostructures and quantum wells grown by using 64Zn and 80Se isotopes and Mg with natural isotope distribution. We present a detailed quantitative secondary ion mass spectrometry (SIMS) analysis, which confirms that an extremely high grade of isotope purification of the ZnSe can be maintained although naturally and enriched Zn and Se elements are used in the same MBE system. This pioneering growth study forms a solid base to generate a spin vacuum ZnSe host crystal that is particularly suited for future studies on the dynamics of localized spins in II/VI heterostructures on a strongly extended coherence time scale.
关键词： Heterostructures,Molecular beam epitaxy,Optical properties,Crystal structure,X-ray diffraction,Isotope purification,Elementary analysis
更新于2025-09-04 15:30:14
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Structural and optical properties of sulfur passivated epitaxial step-graded GaAs <sub/>1-y</sub> Sb <sub/>y</sub> materials
摘要： The impact of bulk and surface defect states on the vibrational and optical properties of step-graded epitaxial GaAs1-ySby (0 ≤ y ≤ 1) materials with and without chemical surface treatment by (NH4)2S was investigated. Tunable antimony (Sb) composition GaAs1-ySby epitaxial layers, grown by solid source molecular beam epitaxy (MBE), were realized on GaAs and Si substrates by varying key growth parameters (e.g., Sb/Ga ?ux ratio, growth temperature). Raman and photoluminescence (PL) spectroscopic analysis of (NH4)2S-treated GaAs1-ySby epitaxial layers revealed composition-independent Raman spectral widths and enhanced PL intensity (1.3×) following (NH4)2S surface treatment, indicating bulk defect-minimal epitaxy and a reduction in the surface recombination velocity corresponding to reduced surface defect sites, respectively. Moreover, quanti?cation of the luminescence recombination mechanisms across a range of measurement temperatures and excitation intensities (i.e., varying laser power) indicate the presence of free-electron to neutral acceptor pair or Sb-defect-related recombination pathways, with detectable bulk defect recombination discernible only in binary GaSb PL spectra. In addition, PL analysis of the short- and long-term thermodynamic stability of sulfur-treated GaAs1-ySby/Al2O3 heterointerfaces revealed an absence of quanti?able atomic interdiffusion or native oxide formation. Leveraging the combined Raman and PL analysis herein, the quality of the heteroepitaxial step-graded epitaxial GaAs1-ySby materials can be optimized for optical devices.
关键词： molecular beam epitaxy,optical properties,structural properties,sulfur passivation,Raman spectroscopy,surface treatment,photoluminescence spectroscopy,GaAs1-ySby
更新于2025-09-04 15:30:14