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The contribution of AsH3: Pre-flow and V/III ratio effects on heteroepitaxially grown GaAs/Ge
摘要： We report the effects of AsH3 (arsine) on morphological, structural, optical and crystalline quality of MOVPE (metal organic vapor phase epitaxy) grown GaAs/Ge heterostructures. AsH3 pre-flow supplied on Ge substrate to have As atoms as a first atomic layer on the surface of Ge substrate. Additionally, the V/III ratio effects of LT-GaAs buffer layer, grown on arsenized Ge substrate, have been analyzed to have reduced APBs (anti-phase boundaries) in the interface between epilayer and Ge substrate. It has been considered that the optimal AsH3 pre-flow duration and V/III ratio of GaAs buffer layer extremely influence the effects of APBs even we have used miss-cut Ge substrate and grown by two-step growth technique to obtain double atomic step. It is shown that without AsH3 pre-flow the surface of GaAs epilayer becomes rougher while it is optically smooth under the longer AsH3 pre-flow. On the other hand, even the surface situation does not change with longer AsH3 pre-flow the structural, optical and crystalline qualities become worse because of the possible presence vacancies of created during the growth. Similar behavior has been observed for the V/III effects of GaAs buffer layer and it has resulted in low full width at half maximum of high-resolution X-ray diffraction and high photoluminescence peak intensity for the optimal V/III ratio.
关键词： Ge,Buffer layer,Arsine,MOVPE,GaAs
更新于2025-09-23 15:23:52
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3D GaN Fins as a Versatile Platform for a-Plane-Based Devices
摘要： GaN fins on GaN-on-sapphire templates are fabricated by continuous mode selective area metalorganic vapor phase epitaxy. The fins exhibit high aspect ratios and smooth nonpolar a-plane sidewalls with an ultra-low threading dislocation density of a few 105 cm?2 making them ideally suited for optoelectronic to electronic applications. A detailed analysis of the inner structure of GaN fins is provided by the help of marker layer experiments and correlation of results from fins fabricated under different growth conditions, leading to the development of a growth model to explain the final geometry and optical as well as electrical properties of these high aspect ratio fins. Distinctly different material properties for the central and outer parts of the fins are detected. Whereas the outer sidewalls represent high quality GaN surfaces with very low defect densities, a strong quenching of near band edge emission (NBE) in the central part of the fins is accompanied by heavy compensation of free electrons. A possible explanation is the incorporation of excessive point defects, like intrinsic defects or carbon impurity. The sidewall regions, however, prove to be highly suitable for device applications due to their strong NBE emission, low dislocation density, and high free carrier concentration.
关键词： marker layers,threading dislocation density,GaN fins,selective-area MOVPE,a-plane sidewalls
更新于2025-09-23 15:22:29
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Interface intermixing and interdiffusion characteristics in MOVPE grown spontaneous AlxGa1-xAs/GaAs (100) superlattice structures using high resolution X-ray diffraction
摘要： Thermal diffusion characteristics in naturally grown ultra-nanoscale superlattice structures have been studied. In absence of any suitable direct experimental tool due to the physical resolution limit, here we rely on the theoretical analysis of x-ray rocking curve simulations coupled with the diffusion equation to arrive at the diffusion characteristics across the interfaces of spontaneously grown AlGaAs/AlGaAs superlattice structures. The simulation approach presented here is a combination of a virtual interdiffusion code and a code on x-ray diffraction. We have obtained the variation in the actual diffusion coefficient as a function of time at different temperatures from the decay rates of the integrated satellite peak intensities. We have also found the diffusion coefficient to be highly nonlinear across the interface with time. The satellite decay equation could fit the experimental data taking the maximum Al composition alone at each time step. The pre exponential factor and the activation enthalpy values for interdiffusion are found out to be 0.17-0.25 cm2 /s and 0.5-0.6 eV for Al diffusion whereas 0.01-0.11 cm2/s and 3.45-3.5 eV for Ga diffusion, respectively in the studied temperature range of 500 oC to 700 oC. The interdiffusivity increases with temperature from 500 oC to 625 oC and decreases for further rise in temperature as the compositional contrast between the two layers decreases significantly at higher temperatures.
关键词： MOVPE,Interdiffusion,HTXRD,AlxGa1-xAs,Spontaneous superlattice
更新于2025-09-23 15:22:29
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[IEEE 2019 Device Research Conference (DRC) - Ann Arbor, MI, USA (2019.6.23-2019.6.26)] 2019 Device Research Conference (DRC) - High-Responsivity Flexible Photodetectors based on MOVPE-MoS <sub/>2</sub>
摘要： We have presented flexible MSM photodetectors based on MOVPE-MoS2. These photosensing devices with high dynamic ranges up to 83dB and high responsivities of up to 550 A/W at low bias make this scalable approach a perfect candidate for future optical sensors in the medical field in which bendable electronics is highly desired. The MOVPE-MoS2 on wafer scale is also interesting for MoS2 FETs with high current on/off ratios of six orders of magnitude, fabricated with standard contact lithography enabling large-scale flexible electronic circuits.
关键词： 2D materials,MoS2,MOVPE,photodetectors,flexible electronics
更新于2025-09-23 15:21:01
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Suppression of dislocation-induced spiral hillocks in MOVPE-grown AlGaN on face-to-face annealed sputter-deposited AlN template
摘要： AlGaN films were grown on face-to-face annealed sputter-deposited AlN/sapphire (FFA Sp-AlN) templates via metalorganic vapor phase epitaxy (MOVPE), and the growth behavior of the AlGaN films was investigated. The sapphire substrates with small off-cut exhibited poor surface flatness of AlGaN grown on the FFA Sp-AlN templates owing to the formation of large hillock structures. To understand the origin of these hillock structures, the crystallinity and surface morphology of conventional fully MOVPE-grown AlN/sapphire (MOVPE-AlN) templates and the FFA Sp-AlN template were comprehensively studied. The screw- and mixed-type threading dislocation density of the FFA Sp-AlN template was estimated to be approximately 1.8 × 106 cm?2, which was two orders of magnitude lower than that of the MOVPE-AlN template. Consequently, the uniquely observed growth of the hillock structures in the FFA Sp-AlN templates was attributed to their low density of screw- and mixed-type threading dislocations. The large surface off-cut sapphire substrates suppressed the hillock structures on the FFA Sp-AlN templates. The improvement in surface flatness resulted in better optical properties of multiple quantum wells grown on the AlGaN layer. These results demonstrate a promising method for achieving highly efficient and cost effective AlGaN based deep ultraviolet light-emitting diodes.
关键词： AlGaN,MOVPE,deep ultraviolet light-emitting diodes,hillock structures,FFA Sp-AlN
更新于2025-09-23 15:19:57
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MOVPE of Large-Scale MoS <sub/>2</sub> /WS <sub/>2</sub> , WS <sub/>2</sub> /MoS <sub/>2</sub> , WS <sub/>2</sub> /Graphene and MoS <sub/>2</sub> /Graphene 2D-2D Heterostructures for Optoelectronic Applications
摘要： Most publications on (opto)electronic devices based on 2D materials rely on single monolayers embedded in classical 3D semiconductors, dielectrics and metals. However, heterostructures of different 2D materials can be employed to tailor the performance of the 2D components by reduced defect densities, carrier or exciton transfer processes and improved stability. This translates to additional and unique degrees of freedom for novel device design. The nearly infinite number of potential combinations of 2D layers allows for many fascinating applications. Unlike mechanical stacking, metal-organic vapour phase epitaxy (MOVPE) can potentially provide large-scale highly homogeneous 2D layer stacks with clean and sharp interfaces. Here, we demonstrate the direct successive MOVPE of MoS2/WS2 and WS2/MoS2 heterostructures on 2” sapphire (0001) substrates. Furthermore, the first deposition of large-scale MoS2/graphene and WS2/graphene heterostructures using only MOVPE is presented and the influence of growth time on nucleation of WS2 on graphene is analysed.
关键词： MOVPE,WS2,MoS2,heterostructures,2D materials,graphene,optoelectronic applications
更新于2025-09-23 15:19:57
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[IEEE 2019 FISE-IEEE/CIGRE Conference - Living the energy Transition (FISE/CIGRE) - Medellin, Colombia (2019.12.4-2019.12.6)] 2019 FISE-IEEE/CIGRE Conference - Living the energy Transition (FISE/CIGRE) - Abating carbon emissions by means of utility-scale photovoltaics and storage: the Duke Energy Progress/Carolinas case study
摘要： A Sn-doped (100) β-Ga2O3 epitaxial layer was grown via metal–organic vapor phase epitaxy onto a single-crystal, Mg-doped semi-insulating (100) β-Ga2O3 substrate. Ga2O3-based metal–oxide–semiconductor field-effect transistors with a 2-μm gate length (L G), 3.4-μm source–drain spacing (LSD), and 0.6-μm gate–drain spacing (LGD) were fabricated and characterized. Devices were observed to hold a gate-to-drain voltage of 230 V in the OFF-state. The gate-to-drain electric field corresponds to 3.8 MV/cm, which is the highest reported for any transistor and surpassing bulk GaN and SiC theoretical limits. Further performance projections are made based on layout, process, and material optimizations to be considered in future iterations.
关键词： MOVPE,β-Ga2O3,MOSFETs,power semiconductor devices
更新于2025-09-23 15:19:57
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Radiation hardness and post irradiation regeneration behavior of GaInAsP solar cells
摘要： Recent developments have renewed the demand for solar cells with increased tolerance to radiation damage. To investigate the specific irradiation damage of 1 MeV electron irradiation in GaInAsP lattice matched to InP for varying In and P contents, a simulation based analysis is employed: by fitting the quantum efficiency and open-circuit voltage simultaneously before and after irradiation, the induced changes in lifetime are detected. Furthermore, the reduction of irradiation damage during regeneration under typical satellite operating conditions for GEO missions (60°C and AM0 illumination) is investigated. A clear decrease of the radiation damage is observed after post irradiation regeneration. This regeneration effect is stronger for increasing InP-fraction. It is demonstrated that the irradiation induced defect recombination coefficient for irradiation with 1 MeV electrons after regeneration for 216 h can be described with a linear function of InP-fraction between 1?10?5 cm2/s for GaAs and 7?10?7 cm2/s for InP. The results show that GaInAsP is a promising material for radiation hard space solar cells.
关键词： Radiation hardness,Annealing,MOVPE,GaInAsP,Space solar cells,Irradiation
更新于2025-09-19 17:13:59
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Effect of dislocation density on optical gain and internal loss of AlGaN-based ultraviolet-B band lasers
摘要： We investigated the dependence of the lasing threshold power density, optical gain, and internal loss on the dislocation density of an optically pumped AlGaN-based ultraviolet-B band laser. Reducing the dislocation density was found to not only increase the optical gain by reducing the non-radiative recombination centers but also reduce the internal loss. Furthermore, this reduction in internal loss was appropriately explained using an increased scattering model based on an increase in the refractive index fluctuations formed by the dislocations.
关键词： MOVPE,lasers,AlGaN,optical properties,UV-B band
更新于2025-09-19 17:13:59
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Metalorganic Vapor Phase Epitaxy (MOVPE) (Growth, Materials Properties, and Applications) || Quantum Dots
摘要： This chapter focuses only on quantum dots (QDs) embedded inside a semiconductor structure, like quantum wells (QWs) or partly quantum wires (QWrs). Freestanding QDs with a much larger application field, which can be prepared from the same material, are not covered in this chapter. The reason for this is that we will write about MOVPE QD preparation only (not, for example, about colloidal, metal, or other freestanding QDs). A research report about the market for the whole family of QDs can be found in [1]. QDs are small pieces of semiconductor nanocrystals (mainly) with sizes in the range from a few to tens of nanometers. The first idea of QDs having properties different from those of the bulk material was published by Ekimov and Onushchenko in 1981 [2]. Their QDs were prepared in colloidal solution, not yet QDs embedded in the heterostructure: “The exciton absorption spectrum of microscopic CuCl crystals grown in a transparent dielectric matrix has been studied. The size of the microscopic crystals was varied in a controlled manner from several tens of angstroms to hundreds of angstroms. There is a short‐wave shift (of up to 0.1 eV) of the exciton absorption lines, caused by a quantum size effect” [2]. During the early 1990s, embedded QDs were prepared by molecular beam epitaxy (MBE) [3–7] in several laboratories, as described in [8]. MOVPE‐grown QDs were reported in 1991 [9, 10], but with little response (12 and 0 citations, respectively). MBE seems to be more suitable for attaining an exact layer thickness down to fractions of a monolayer. QD MOVPE papers published later [11–14] attracted much more interest. An attempt to realize industrial MOVPE‐prepared QD‐based semiconductor lasers for fiber optic telecommunications appeared during the first years of this century (EU project DOTCOM 2002–05), but without a real impact on industrial production.
关键词： quantum dots,semiconductor lasers,optical properties,growth procedures,MOVPE
更新于2025-09-19 17:13:59