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Remote epitaxy has drawn attention as it offers epitaxy of functional materials that can be released from the substrates with atomic precision, thus enabling production and heterointegration of flexible, transferrable, and stackable freestanding single-crystalline membranes. In addition, the remote interaction of atoms and adatoms through two-dimensional (2D) materials in remote epitaxy allows investigation and utilization of electrical/chemical/physical coupling of bulk (3D) materials via 2D materials (3D-2D-3D coupling). Here, we unveil the respective roles and impacts of the substrate material, graphene, substrate-graphene interface, and epitaxial material for electrostatic coupling of these materials, which governs cohesive ordering and can lead to single-crystal epitaxy in the overlying film. We show that simply coating a graphene layer on wafers does not guarantee successful implementation of remote epitaxy, since atomically precise control of the graphene-coated interface is required, and provides key considerations for maximizing the remote electrostatic interaction between the substrate and adatoms. This was enabled by exploring various material systems and processing conditions, and we demonstrate that the rules of remote epitaxy vary significantly depending on the ionicity of material systems as well as the graphene-substrate interface and the epitaxy environment. The general rule of thumb discovered here enables expanding 3D material libraries that can be stacked in freestanding form.

Although conventional homoepitaxy forms high-quality epitaxial layers1-5, the limited set of material systems for commercially available wafers restricts the range of materials that can be grown homoepitaxially. At the same time, conventional heteroepitaxy of lattice-mismatched systems produces dislocations above a critical strain energy to release the accumulated strain energy as the film thickness increases. The formation of dislocations, which severely degrade electronic/photonic device performances6-8, is fundamentally unavoidable in highly lattice-mismatched epitaxy9-11. Here, we introduce a unique mechanism of relaxing misfit strain in heteroepitaxial films that can enable effective lattice engineering. We have observed that heteroepitaxy on graphene-coated substrates allows for spontaneous relaxation of misfit strain owing to the slippery graphene surface while achieving single-crystalline films by reading the atomic potential from the substrate. This spontaneous relaxation technique could transform the monolithic integration of largely lattice-mismatched systems by covering a wide range of the misfit spectrum to enhance and broaden the functionality of semiconductor devices for advanced electronics and photonics.

Complex-oxide materials exhibit a vast range of functional properties desirable for next-generation electronic, spintronic, magnetoelectric, neuromorphic, and energy conversion storage devices1-4. Their physical functionalities can be coupled by stacking layers of such materials to create heterostructures and can be further boosted by applying strain5-7. The predominant method for heterogeneous integration and application of strain has been through heteroepitaxy, which drastically limits the possible material combinations and the ability to integrate complex oxides with mature semiconductor technologies. Moreover, key physical properties of complex-oxide thin films, such as piezoelectricity and magnetostriction, are severely reduced by the substrate clamping effect. Here we demonstrate a universal mechanical exfoliation method of producing freestanding single-crystalline membranes made from a wide range of complex-oxide materials including perovskite, spinel and garnet crystal structures with varying crystallographic orientations. In addition, we create artificial heterostructures and hybridize their physical properties by directly stacking such freestanding membranes with different crystal structures and orientations, which is not possible using conventional methods. Our results establish a platform for stacking and coupling three-dimensional structures, akin to two-dimensional material-based heterostructures, for enhancing device functionalities8,9.

The demand for improved electronic and optoelectronic devices has fuelled the development of epitaxial growth techniques for single-crystalline semiconductors. However, lattice and thermal expansion coefficient mismatch problems limit the options for growth and integration of high-efficiency electronic and photonic devices on dissimilar materials. Accordingly, advanced epitaxial growth and layer lift-off techniques have been developed to address issues relating to lattice mismatch. Here, we review epitaxial growth and layer-transfer techniques for monolithic integration of dissimilar single-crystalline materials for application in advanced electronic and photonic devices. We also examine emerging epitaxial growth techniques that involve two-dimensional materials as an epitaxial release layer and explore future integrated computing systems that could harness both advanced epitaxial growth and lift-off approaches. This Review Article examines the development of epitaxial growth and layer transfer techniques for monolithic integration of dissimilar single-crystalline materials for application in advanced electronic and photonic devices.

The ground-breaking demonstration of the electric field effect in graphene reported more than a decade ago prompted the strong push towards the commercialization of graphene as evidenced by a wealth of graphene research, patents and applications. Graphene flake production capability has reached thousands of tonnes per year, while continuous graphene sheets of tens of metres in length have become available. Various graphene technologies developed in laboratories have now transformed into commercial products, with the very first demonstrations in sports goods, automotive coatings, conductive inks and touch screens, to name a few. Although challenges related to quality control in graphene materials remain to be addressed, the advancement in the understandings of graphene will propel the commercial success of graphene as a compelling technology. This Review discusses the progress towards commercialization of graphene for the past decade and future perspectives. This Review reflects on the 15 years of advances in the field of 2D materials towards commercialization of graphene and its future perspectives.

Heterogeneous self-assembly of III–V nanostructures on inert two-dimensional monolayer materials enables novel hybrid nanosystems with unique properties that can be exploited for low-cost and low-weight flexible optoelectronic and nanoelectronic device applications. Here, the pseudo-van der Waals epitaxy (vdWE) growth parameter space for heterogeneous integration of InAs nanowires (NWs) with continuous films of single layer graphene (SLG) via metalorganic chemical vapor deposition (MOCVD) is investigated. The length, diameter, and number density of NWs, as well as areal coverage of parasitic islands, are quantified as functions of key growth variables including growth temperature, V/III ratio, and total flow rate of metalorganic and hydride precursors. A compromise between self-assembly of high aspect ratio NWs comprising high number density arrays and simultaneous minimization of parasitic growth coverage is reached under a selected set of optimal growth conditions. Exploration of NW crystal structures formed under various growth conditions reveals that a characteristic polytypic and disordered lattice is invariant within the explored parameter space. A growth evolution study reveals a gradual reduction in both axial and radial growth rates within the explored timeframe for the optimal growth conditions, which is attributed to a supply-limited competitive growth regime. Two strategies are introduced for further growth optimization. Firstly, it is shown that the absence of a pre-growth in situ arsine surface treatment results in a reduction of parasitic island coverage by factor of ∼0.62, while NW aspect ratio and number densities are simultaneously enhanced. Secondly, the use of a two-step flow-modulated growth procedure allows for realization of dense fields of high aspect ratio InAs NWs. As a result of the applied studies and optimization of the growth parameter space, the highest reported axial growth rate of 840 nm min−1 and NW number density of ∼8.3 × 108 cm−2 for vdWE of high aspect ratio (>80) InAs NW arrays on graphitic surfaces are achieved. This work is intended to serve as a guide for vdWE of self-assembled III–V semiconductor NWs such as In-based ternary and quaternary alloys on functional two-dimensional monolayer materials, toward device applications in flexible optoelectronics and tandem-junction photovoltaics.

Artificial auxetic sweat ducts enable electronic skin sensors to perform reliable and noninvasive health monitoring over a week., Electronic skins (e-skins)—electronic sensors mechanically compliant to human skin—have long been developed as an ideal electronic platform for noninvasive human health monitoring. For reliable physical health monitoring, the interface between the e-skin and human skin must be conformal and intact consistently. However, conventional e-skins cannot perfectly permeate sweat in normal day-to-day activities, resulting in degradation of the intimate interface over time and impeding stable physical sensing. Here, we present a sweat pore–inspired perforated e-skin that can effectively suppress sweat accumulation and allow inorganic sensors to obtain physical health information without malfunctioning. The auxetic dumbbell through-hole patterns in perforated e-skins lead to synergistic effects on physical properties including mechanical reliability, conformability, areal mass density, and adhesion to the skin. The perforated e-skin allows one to laminate onto the skin with consistent homeostasis, enabling multiple inorganic sensors on the skin to reliably monitor the wearer’s health over a period of weeks.

We report the first demonstration of MOVPE-grown inverted metamorphic (IMM) cells with QDs embedded in the middle GaAs sub-cell. The IMM cells were fabricated on full 4″ wafer using Epitaxial Lift off (ELO) technology. GaAs sub-cell embedded with 10 and 20 periods of InAs/GaP strain compensated QDs showed increase in current with number of QD periods. The single junction GaAs sub cell embedded with 20 periods of InAs/GaP strain compensated QDs showed 3.2% relative increase in JSC in comparison with control sample without QDs. Integrated short circuit (JSC) from measurements of external quantum efficiency (EQE) of currents showed a 65% increase in sub-band collection in the GaAs sub-cell when the number of QD layers increased from 10 to 20. IMM cells with QD's embedded in the middle cell showed minimal loss in open circuit voltage (VOC) in comparison to control sample without QDs. An efficiency of 30% under 1-sun AM0 spectrum was obtained for IMM cells with 10 xs of InAs/GaP QDs in GaAs sub-cell. Quantum efficiency remaining factor of > 95% in the QD absorption region (940 nm) was measured for IMM devices with InAs/GaAs QD enhanced GaAs sub-cells irradiated with 1 MeV electrons under 2E15 /cm2 fluence.

The rediscovery of graphene in 2004 triggered an explosive expansion of research on various van der Waals (vdW) materials. The atomic layers of these vdW materials do not have surface crystal defects and are bonded by weak vdW interactions, thus the vdW materials can be stacked onto each other to form vdW heterojunction structures without needing to consider the lattice mismatch issue. In addition, the broad library of vdW materials makes it possible to design diverse types of heterojunctions with a wide range of band alignments, bandgaps, and electron affinities. Vertical vdW heterostructures especially offer numerous possibilities for the realization of high-performance electronic and optoelectronic devices. Therefore, these vdW heterostructures have received significant attention, and extensive relevant experimental results have been reported in the past few years. In this review, we first introduce the transfer techniques to form vdW heterojunction structures. Next, we discuss recent progress in vdW heterostructure-based electronic and optoelectronic devices, including vertical field effect transistors, negative differential resistance devices, memories, photodetectors, photovoltaic devices, and light-emitting diodes. Finally, we conclude this review by discussing the current challenges facing vdW heterojunction structure-based devices and our perspective on future research directions.

Nonlinear oxides such as LiNbO3 have found many applications in both conventional electro-optics and quantum optics. In this work, we demonstrate the van der Waals and remote epitaxy of LiNbO3 films on muscovite mica and graphene-buffered sapphire, respectively, by pulsed laser deposition. Structural analysis shows that the epitaxial relation in van der Waals epitaxy is LiNbO3 (0001) || mica (001) and LiNbO3 [ 01 1 ¯ 0] || mica [010] with LiNbO3 [ 10 1 ¯ 0] || mica [010], a 60°-rotated twin structure. The relation in remote epitaxy is LiNbO3 (0001) || sapphire (0001) and LiNbO3 [ 01 1 ¯ 0] || sapphire [ 01 1 ¯ 0] with twin structure LiNbO3 [ 1 ¯ 010] || sapphire [ 01 1 ¯ 0]. Furthermore, in remote epitaxy, Raman scattering analysis confirms the existence of graphene after deposition. Finally, we find that the oxygen partial pressure influences the presence of impurity phases significantly. The successful demonstration of van der Waals and remote epitaxy promises the feasibility of developing thin film LiNbO3 on demanded substrates toward scalable electro-optics.

No claim to original U.S. Government Works. Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple monolayers of wafer-scale (5-centimeter diameter) 2D materials by splitting single stacks of thick 2D materials grown on a single wafer. Wafer-scale uniformity of hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, and molybdenum diselenide monolayers was verified by photoluminescence response and by substantial retention of electronic conductivity. We fabricated wafer-scale van der Waals heterostructures, including field-effect transistors, with single-atom thickness resolution., National Science Foundation (U.S.) (Grant CMMI-1825731), National Science Foundation (U.S.) (Grant CMMI-1825256), National Science Foundation (U.S.) (Grant DMR-1700137), United States. Office of Naval Research (Grant N00014-16-1-2657)

Hybrid heterostructures are essential for functional device systems. The advent of 2D materials has broadened the material set beyond conventional 3D material-based heterostructures. It has triggered the fundamental investigation and use in applications of new coupling phenomena between 3D bulk materials and 2D atomic layers that have unique van der Waals features. Here we review the state-of-the-art fabrication of 2D and 3D heterostructures, present a critical survey of unique phenomena arising from forming 3D/2D interfaces, and introduce their applications. We also discuss potential directions for research based on these new coupled architectures. Integrating 3D bulk materials with 2D layered materials can harness promising properties and unique functions. This Review discusses the progress in the fabrication, physical coupling and potential applications of 3D/2D hybrid heterostructures.

Band alignment transition from type-I to type-II of InP/In 0.48 Ga 0.52 P quantum dots (QDs) is observed by modifying the geometrical factors of the dome-shaped QDs. Strain distribution in InP/In 0.48 Ga 0.52 P QD is calculated using a valence force field (VFF) model. With the strain Hamiltonian from the VFF model, electrical structures of the QDs are obtained using 8-band k•p model. The results from this theoretical study show that the band alignment of the InP/In 0.48 Ga 0.52 P QDs can be tailored from type-I to type-II by controlling the size of the QDs, and flat valence band can be achieved at certain values of height and width of the QDs. In addition, InP/In 0.48 Ga 0.52 QDs of various sizes with the same effective bandgap but different band alignment is observed.

Growth of type-II InP quantum dots in wide bandgap InGaP $(\mathrm{E}_{G}=\mathrm{1.85} \ \mathrm{eV})$ for intermediate band solar cell applications is studied, grown via Aixtron close-coupled showerhead metal-organic chemical vapor deposition system. Theoretical calculation and optical characterizations verify type-II band alignment, showing approximately 300 meV electron confinement in the conduction band and around 5 meV potential barrier for holes in the valence band. AFM measurements predominantly show type-II dots (dot height greater than 15 nm), which is further verified by a single QD peak with narrow full width at half maximum obtained by photoluminescence measurements. Dot density of $0.7 \ \mathrm{x}10^{10}\ \mathrm{cm}^{-2}$ is measured with diameter and height of $-56\pm 10 \ \mathrm{nm}$ and $18 \ \pm \ 2.8 \ \mathrm{nm}$, respectively. This quantum dot system promises a more ideal band alignment for intermediate band assisted photon absorption and higher two-step photon absorption (TSPA) temperatures. Here, we observe TSPA response up to 200 K for a solar cell with 5x layers of InP QDs in the intrinsic region.

The fabricated single junction InGaP photovoltaic devices show an overall 30% conversion efficiency under 1.27 uW/cm2 illumination. The development not only enables long lifetime radio-isotope based batteries but also, more important for the daily life, has the potential to promote the concept of the internet of things by efficiently powering indoor wireless sensors. To reduce the dark current and increase the absorption at longer wavelengths ( $> 550\ \mathbf{nm}$ ), several parameters including doping and thickness are optimized for the device design. Additional current-voltage characteristics under dark conditions and external quantum efficiency were also performed in order to evaluate the performance of the InGaP photovoltaic cells.

The realization of the concept of the intermediate band solar cell (IBSC) requires that two-step photon absorption dominates at room temperature. To increase two step photon absorption (TSPA), an InAs/GaAs/Alo.3GaAs quantum dot in a well (Dwell) structure is used to reduce thermal escape of carriers. The Dwell structure shows decreased TSPA with increasing temperature because of faster thermal escape. With an increased electron ground state barrier height relative to Al 0.3 GaAs, the observable TSPA occurs up to 80K. The extracted thermal activation energy from temperature dependent TSPA is between 80−95 me V, which is associated with holes escape processes. Charge separation along the growth direction reduces the recombination rate in the IB. The stable TSPA observed at −2V reverse bias may be a balance between the reduced recombination rate and increased tunneling rate.

In this work, a Sentaurus TCAD model of inverted metamorphic triple junction solar cells is demonstrated along with experimental 3J current-voltage and external quantum efficiency measurements for the purpose of predicting end-of-life efficiency improvement from incorporating quantum wells or quantum dots into a metamorphic In 0.3 Ga 0.7 As sub cell in a 3J solar cell. A radiation-hard “end-of-life optimized” design is presented and end-of life efficiency enhancement is predicted from calculated QD and QW absorption coefficients. The resulting QW enhanced solar cell design is predicted to have a 6% relative efficiency enhancement over the optimized baseline design.

We present a method of epitaxially growing thermodynamically stable gallium nitride (GaN) nanorods via metal-organic chemical vapor deposition (MOCVD) by invoking a two-step self-limited growth (TSSLG) mechanism. This allows for growth of nanorods with excellent geometrical uniformity with no visible extended defects over a 100 mm sapphire (Al2O3) wafer. An ex-situ study of the growth morphology as a function of growth time for the two self-limiting steps elucidate the growth dynamics, which show that formation of an Ehrlich-Schwoebel barrier and preferential growth in the c-plane direction governs the growth process. This process allows monolithic formation of dimensionally uniform nanowires on templates with varying filling matrix patterns for a variety of novel electronic and optoelectronic applications. A color tunable phosphor-free white light LED with a coaxial architecture is fabricated as a demonstration of the applicability of these nanorods grown by TSSLG.

This paper presents a dynamic modeling, simulation, and analysis of a Battery Electric Vehicle (BEV) according to vehicle dynamic characteristics. Mathematical model variants for the components of BEVs can be modeled and investigated using the Matlab/Simulink software. In order to compare the dynamic performance of BEVs under inverter fault and normal conditions, the CarSim co-simulation platform is configured with real vehicle calibration data. Using this approach, it was possible to quickly check for dynamic performance issues of an electric vehicle without incurring the time delay and cost. The simulation results such as motor output, vehicle speed/acceleration, and propulsion forces are discussed and compared for each drive mode.

Intermediate band solar cells promise improved efficiencies beyond the Shockley-Queisser limit by utilizing an intermediate band formed within the bandgap of a single junction solar cell. InP quantum dots (QDs) in an In0.49Ga0.51P host are a promising material system for this application, but two-step photon absorption has not yet been demonstrated. InP QDs were grown via metalorganic chemical vapor deposition, and a density, a diameter, and a height of 0.7 × 1010 cm−2, 56 ± 10 nm, and 18 ± 2.8 nm, respectively, were achieved. Time-resolved photoluminescence measurements show a long carrier lifetime of 240 ns, indicating a type-II band alignment of these InP quantum dots. Several n-i-p In0.49Ga0.51P solar cells were grown with both 3 and 5 layers of InP QDs in the i-region. While the solar cells showed an overall loss in short circuit current compared to reference cells due to emitter degradation, a sub-bandgap enhancement of 0.11 mA/cm2 was clearly observed, due to absorption and collection from the InP QDs. Finally, two-step photon absorption experiments have shown unambiguous photocurrent generation involving an intermediate band within the bandgap at temperatures up to 250 K.Intermediate band solar cells promise improved efficiencies beyond the Shockley-Queisser limit by utilizing an intermediate band formed within the bandgap of a single junction solar cell. InP quantum dots (QDs) in an In0.49Ga0.51P host are a promising material system for this application, but two-step photon absorption has not yet been demonstrated. InP QDs were grown via metalorganic chemical vapor deposition, and a density, a diameter, and a height of 0.7 × 1010 cm−2, 56 ± 10 nm, and 18 ± 2.8 nm, respectively, were achieved. Time-resolved photoluminescence measurements show a long carrier lifetime of 240 ns, indicating a type-II band alignment of these InP quantum dots. Several n-i-p In0.49Ga0.51P solar cells were grown with both 3 and 5 layers of InP QDs in the i-region. While the solar cells showed an overall loss in short circuit current compared to reference cells due to emitter degradation, a sub-bandgap enhancement of 0.11 mA/cm2 was clearly observed, due to absorption and collection from the InP ...

In transportation and use environments, electronic appliances, especially those that are large and heavy, suffer many different types of mechanical shocks. Generally, to prevent damage to the products from severe shocks, various cushion materials used for packaging have been widely utilized. However, the external shape of electronic appliances is complex, and the mass distribution of the inside parts is unbalanced. Consequently, it is not easy when using empirical approaches to design the cushioning package to ensure that it has a high absorption of shock energy. In this study, experimental and analytical approaches have been used to propose an effective design process for the optimization of cushioning packages so that they have less volume and a greater cushioning ability. An examination of the optimization of cushioning package was conducted for a large-size refrigerator with a weight of more than 100 kg to demonstrate the usefulness of the proposed method; findings from the study show that the volume reduction of a package was as much as 22% with the reduction of maximum acceleration at 25%.

A typical example of entrepreneurship is revealed through business start-up whereas a core principle of creative economy is revealed in the multilateral aspect such as research, creation, etc. Entrepreneurship contributes to job creation and national economy growth through the business start-up. And it also creates to individual development such employment, income increases, etc.Key countries overseas consider entrepreneurship as a core factor of national competitiveness, actively encouraging the fosterage of entrepreneurship. U.S. approaches toward entrepreneurship education as a lifelong learning from elementary school to college and career training course. In Europe, the Oslo Agenda for Entrepreneurship Education (2006) in the EU countries for a resolution for nurturing the entrepreneurship through the education.A policy solely aimed at the increases of entrepreneurship birth is too limited, requiring a paradigm shift in policy in response to nurturing the entrepreneurship as a foundation of business start-up. The policy focusing on start-up activities and cases is only existed to create a short-term outcome. The currently existing ‘Start-up Pull’ strategy focused on a short-term outcome now needs to shift into ‘Entrepreneurship Push’ strategy for the dissemination; accordingly, a new entrepreneurship index needs to be developed for the understanding and measurement.

Vertically aligned InGaN/GaN nanorod (NR)-based phosphor-free light emitting diodes (LEDs) using SiO2 nanohole patterns are demonstrated. The highly ordered SiO2 nanoholes were realized on a 2 μm-thick n+GaN template by a two-step dry etching process. The use of C4F8/O2/Ar plasma chemistries under the low pressure is found to greatly enlarge the bottom diameter of each hole, exhibiting high aspect ratio (AR ∼ 9) and vertical etch profile (∼89°). SAG technique was used to define the height of the GaN NRs while the width is determined by the trimethylgallium flow rate and growth temperature. An LED structure consisted of three-pairs of InGaN/GaN quantum well and AlGaN electron blocking layer on the sidewall of the nanorod in a core-shell structure. The wavelengths were successfully tuned by controlling pitches of the rods, which was caused by the different growth rate and indium incorporation of conformally overgrown InGaN multiquantum wells. At the operating current density of 1.5 A/cm2 (65 mA), NR-based s...

Spin injection and precession in bulk wurtzite $n$-GaN with different doping densities are demonstrated with a ferromagnetic MnAs contact using the three-terminal Hanle measurement technique. Theoretical analysis using minimum fitting parameters indicates that the spin accumulation is primarily in the $n$-GaN channel rather than at the ferromagnet (FM)/semiconductor (SC) interface states. Spin relaxation in GaN is interpreted in terms of the D'yakonov-Perel mechanism, yielding a maximum spin lifetime of 44 ps and a spin diffusion length of 175 nm at room temperature. Our results indicate that epitaxial ferromagnetic MnAs is a suitable high-temperature spin injector for GaN.

We demonstrate high temperature electrical spin injection and detection in degenerately p-doped GaAs in vertical spin valves using valence band electron tunneling. The maximum measured magnetoresistance at 10 and 300 K is 40% and similar to 1%, respectively. Spin relaxation in these devices was found to be relatively insensitive to temperature (T) for T> 125 K. The spin injection and detection efficiencies are mostly dominated by the ferromagnetic contact polarization and spin independent transport at the ferromagnet/semiconductor interface. (C) 2010 [doi:10.1063/1.3524820]

The reverse bias leakage characteristics of InGaN/GaN light emitting diodes (LEDs) grown on Si (111) were investigated as a function of two factors: (1) bulk depletion width and (2) V-pit size. The reverse leakage current showed a decreasing trend with an increase in V-pit size, given a fixed depletion width. Atomic probe tomography was used to verify that a reduction in electric field near the vicinity of threading dislocations suppresses field-assisted carrier emission, reducing reverse leakage. Calculations using the appropriate theory show a reasonable agreement with the experimental results. These findings further elucidate the role of V-pits as passivation for reverse leakage paths and may be useful for not only LEDs but GaN-based power devices as well.

We report the direct measurement of spin transport characteristics in a GaN spin valve, with a relatively defect-free single GaN nanowire (NW) as the channel and FeCo/MgO as the tunnel barrier spin contact. Hanle spin precession and non-local transport measurements are made in an unintentionally doped nanowire spin valves. Spin diffusion length and spin lifetime values of 260 nm and 100 ps, respectively, are derived. Appropriate control measurements have been made to verify spin injection, transport, and detection.

Gate control and amplification of magnetoresistance are demonstrated at room temperature in a fully epitaxial three-terminal GaAs-based device. In addition to the two ferromagnetic spin injector and detector electrodes of a MnAs/AlAs/GaAs:Mn/AlAs/MnAs vertical spin valve, a third non-magnetic gate electrode (Ti/Au) is placed directly on top of the heavily p-doped GaAs channel layer. The magnetoresistance of the device can be amplified to reach values as high as 500% at room temperature with the application of a bias to the gate terminal, which modulates the spin selectivity of the tunnel barriers. The experimental results are modeled by solving spin drift-diffusion and tunneling equations self consistently. (C) 2011 American Institute of Physics. [doi:10.1063/13652765]

The magnetoresistance of two terminal lateral semiconductor spin valves with respect to varying mesa size is studied. It is shown theoretically that extended regions outside the spin-current path can act as an additional source of spin-relaxation, decreasing the magnetoresistance response. From a simplified expression of magnetoresistance derived from spin-diffusion equations, we show that it is important to etch away these extended regions for devices with channel lengths much smaller than the spin-diffusion length in order to achieve maximum magnetoresistance. Preliminary experimental data on a two terminal local spin valve are in good agreement with the theory established in this article.

The control of magnetoresistance of a lateral spin valve with bias applied to a gate placed outside the channel region is demonstrated. The spin valve channel consists of an InAs/In0.53Ga0.47As/In0.52Al0.48As two-dimensional electron gas lattice matched to (001) InP. The polarizer and analyzer contacts are made with 35 nm type B MnAs/In0.52Al0.48As Schottky tunnel barriers. The magnetoresistance changes from 0.14% to 4% at 10 K in a device in which the spin transport is in the direction of magnetization of the polarizer and analyzer contacts. The effect is absent in a GaAs channel spin valve and other control devices indicating that the change in magnetoresistance is due to Rashba spin-orbit coupling.

The heteroepitaxial growth of type-B ferromagnetic MnAs on InP and lattice matched In0.53Ga0.47As has been investigated for the first time. In situ reflection high energy electron diffraction during molecular beam epitaxy and atomic force microscopy are used to study the reconstruction and morphology, respectively, of the MnAs surface. The in-plane magnetic properties of the film are studied by magneto-optic Kerr effect measurements. The Curie temperature is estimated to be 315 K. The coercivity of 35 nm films measured at room temperature and 10 K are 860 Oe and 1410 Oe, respectively. The measured in-plane magnetocrystalline anisotropy constants Ku1 and Ku2 for the film are 2.747 × 106 and 7.086 × 106 erg cm−3, respectively. The magnetization and hysteresis in the out-of-plane direction are characterized by a saturation magnetic field of 1.2 T and coercivity of 1600 Oe at 10 K.

We demonstrate a graphene/III-V hybrid diode optical modulator working over a large frequency range from NIR to THz. The hybrid diode is achieved by heterogeneous integration of graphene and III-V heterostructures by remote epitaxy growth.