Showing papers on "Epitaxy published in 2002"
TL;DR: The synthesis of core–multishell structures, including a high-performance coaxially gated field-effect transistor, indicates the general potential of radial heterostructure growth for the development of nanowire-based devices.
Abstract: Semiconductor heterostructures with modulated composition and/or doping enable passivation of interfaces and the generation of devices with diverse functions. In this regard, the control of interfaces in nanoscale building blocks with high surface area will be increasingly important in the assembly of electronic and photonic devices. Core-shell heterostructures formed by the growth of crystalline overlayers on nanocrystals offer enhanced emission efficiency, important for various applications. Axial heterostructures have also been formed by a one-dimensional modulation of nanowire composition and doping. However, modulation of the radial composition and doping in nanowire structures has received much less attention than planar and nanocrystal systems. Here we synthesize silicon and germanium core-shell and multishell nanowire heterostructures using a chemical vapour deposition method applicable to a variety of nanoscale materials. Our investigations of the growth of boron-doped silicon shells on intrinsic silicon and silicon-silicon oxide core-shell nanowires indicate that homoepitaxy can be achieved at relatively low temperatures on clean silicon. We also demonstrate the possibility of heteroepitaxial growth of crystalline germanium-silicon and silicon-germanium core-shell structures, in which band-offsets drive hole injection into either germanium core or shell regions. Our synthesis of core-multishell structures, including a high-performance coaxially gated field-effect transistor, indicates the general potential of radial heterostructure growth for the development of nanowire-based devices.
2,022 citations
TL;DR: An N-doped p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating, N-O substrate as discussed by the authors.
Abstract: An N-doped, p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating ZnO substrate. Hall-effect and conductivity measurements on the layer give: resistivity=4×101 Ω cm; hole mobility=2 cm2/V s; and hole concentration=9×1016 cm−3. Photoluminescence measurements in this N-doped layer show a much stronger peak near 3.32 eV (probably due to neutral acceptor bound excitons), than at 3.36 eV (neutral donor bound excitons), whereas the opposite is true in undoped ZnO. Calibrated, secondary-ion mass spectroscopy measurements show an N surface concentration of about 1019 cm−3 in the N-doped sample, but only about 1017 cm−3 in the undoped sample.
1,237 citations
TL;DR: In this article, metalorganic vapor phase epitaxial growth and structural and photoluminescent characteristics of ZnO nanorods were reported, and they were grown on Al2O3(00⋅1) substrates at 400°C without employing any metal catalysts usually needed in other methods.
Abstract: We report metalorganic vapor-phase epitaxial growth and structural and photoluminescent characteristics of ZnO nanorods. The nanorods were grown on Al2O3(00⋅1) substrates at 400 °C without employing any metal catalysts usually needed in other methods. Electron microscopy revealed that nanorods with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates. The mean diameter of the nanorods is as narrow as 25 nm. In addition, x-ray diffraction measurements clearly show that ZnO nanorods were grown epitaxially with homogeneous in-plane alignment as well as a c-axis orientation. More importantly, from photoluminescence spectra of the nanorods strong and narrow excitonic emission and extremely weak deep level emission were observed, indicating that the nanorods are of high optical quality.
1,136 citations
Patent•
31 Oct 2002
TL;DR: A natural superlattice homologous single crystal thin film, characterized in that it comprises a composite oxide which is represented by the formula M1M2O3(ZnO)m, is a natural number of 1 or more as discussed by the authors.
Abstract: A natural superlattice homologous single crystal thin film, characterized in that it comprises a composite oxide which is represented by the formula M1M2O3(ZnO)m, wherein M1 is at least one of Ga, Fe, Sc, In, Lu, Yb, Tm, Er, Ho and Y, M2 is at least one of Mn, Fe, Ga, In and Al, and m is a natural number of 1 or more, and has been grown epitaxially on an epitaxial thin film formed on a single crystal substrate, or on said single crystal substrate from which said epitaxial thin film has disappeared, or on a ZnO single crystal; a method for preparing the natural superlattice thin film which comprises depositing the composite oxide, and diffusing the resultant laminated film by heating it. The natural superlattice homologous single crystal thin film is suitably used in an optical device, an electronic device, an X-ray optical device and the like.
1,090 citations
TL;DR: In this paper, the structural, mechanical, thermal, and chemical properties of substrates used for gallium nitride (GaN) epitaxy are compiled, and the properties of GaN films deposited on these substrates are reviewed.
Abstract: In this review, the structural, mechanical, thermal, and chemical properties of substrates used for gallium nitride (GaN) epitaxy are compiled, and the properties of GaN films deposited on these substrates are reviewed. Among semiconductors, GaN is unique; most of its applications uses thin GaN films deposited on foreign substrates (materials other than GaN); that is, heteroepitaxial thin films. As a consequence of heteroepitaxy, the quality of the GaN films is very dependent on the properties of the substrate—both the inherent properties such as lattice constants and thermal expansion coefficients, and process induced properties such as surface roughness, step height and terrace width, and wetting behavior. The consequences of heteroepitaxy are discussed, including the crystallographic orientation and polarity, surface morphology, and inherent and thermally induced stress in the GaN films. Defects such as threading dislocations, inversion domains, and the unintentional incorporation of impurities into the epitaxial GaN layer resulting from heteroepitaxy are presented along with their effect on device processing and performance. A summary of the structure and lattice constants for many semiconductors, metals, metal nitrides, and oxides used or considered for GaN epitaxy is presented. The properties, synthesis, advantages and disadvantages of the six most commonly employed substrates (sapphire, 6H-SiC, Si, GaAs, LiGaO 2 , and AlN) are presented. Useful substrate properties such as lattice constants, defect densities, elastic moduli, thermal expansion coefficients, thermal conductivities, etching characteristics, and reactivities under deposition conditions are presented. Efforts to reduce the defect densities and to optimize the electrical and optical properties of the GaN epitaxial film by substrate etching, nitridation, and slight misorientation from the (0 0 0 1) crystal plane are reviewed. The requirements, the obstacles, and the results to date to produce zincblende GaN on 3C-SiC/Si(0 0 1) and GaAs are discussed. Tables summarizing measures of the GaN quality such as XRD rocking curve FWHM, photoluminescence peak position and FWHM, and electron mobilities for GaN epitaxial layers produced by MOCVD, MBE, and HVPE for each substrate are given. The initial results using GaN substrates, prepared as bulk crystals and as free-standing epitaxial films, are reviewed. Finally, the promise and the directions of research on new potential substrates, such as compliant and porous substrates are described.
810 citations
TL;DR: A new model of crystal growth is presented that describes the phenomena on atomic length and diffusive time scales in a natural manner and enables access to time scales much larger than conventional atomic methods.
Abstract: A new model of crystal growth is presented that describes the phenomena on atomic length and diffusive time scales. The former incorporates elastic and plastic deformation in a natural manner, and the latter enables access to time scales much larger than conventional atomic methods. The model is shown to be consistent with the predictions of Read and Shockley for grain boundary energy, and Matthews and Blakeslee for misfit dislocations in epitaxial growth.
751 citations
TL;DR: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy as discussed by the authors, and growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction.
Abstract: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7–1.0 eV. In contrast, no PL was observed, even by high power excitation, at ∼1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7–1.0 eV, and the discrepancy could be attributed to the difference in crystallinity.
692 citations
TL;DR: In this paper, the authors reported on the realization of wide band gap (5-6 eV), single-phase, metastable, and epitaxial MgxZn1−xO thin-film alloys grown on sapphire by pulsed laser deposition.
Abstract: We report on the realization of wide band gap (5–6 eV), single-phase, metastable, and epitaxial MgxZn1−xO thin-film alloys grown on sapphire by pulsed laser deposition We found that the composition, structure, and band gaps of the MgxZn1−xO thin-film alloys depend critically on the growth temperature The structural transition from hexagonal to cubic phase has been observed for (Mg content greater than 50 at %) (1⩾x⩾05) which can be achieved by growing the film alloys in the temperature range of 750 °C to room temperature Interestingly, the increase of Mg content in the film has been found to be beneficial for the epitaxial growth at relatively low growth temperature in spite of a large lattice mismatch between sapphire and cubic MgZnO alloys
547 citations
532 citations
TL;DR: In this paper, structural characteristics of nonpolar (1120) a-plane GaN thin films grown on (1102) r-plane sapphire substrates via metalorganic chemical vapor deposition were described.
Abstract: In this letter we describe the structural characteristics of nonpolar (1120) a-plane GaN thin films grown on (1102) r-plane sapphire substrates via metalorganic chemical vapor deposition. Planar growth surfaces have been achieved and the potential for device-quality layers realized by depositing a low temperature nucleation layer prior to high temperature epitaxial growth. The in-plane orientation of the GaN with respect to the r-plane sapphire substrate was confirmed to be [0001]GaN‖[1101]sapphire and [1100]GaN‖[1120]sapphire. This relationship is explicitly defined since the polarity of the a-GaN films was determined using convergent beam electron diffraction. Threading dislocations and stacking faults, observed in plan-view and cross-sectional transmission electron microscope images, dominated the a-GaN microstructure with densities of 2.6×1010 cm−2 and 3.8×105 cm−1, respectively. Submicron pits and crystallographic terraces were observed on the optically specular a-GaN surface with atomic force m...
488 citations
TL;DR: The electric field dependence of the domain wall velocity demonstrates that domain wall motion in ferroelectric thin films is a creep process, with the critical exponent mu close to 1.The dimensionality of the films suggests that disorder is at the origin of the observed creep behavior.
Abstract: Ferroelectric switching and nanoscale domain dynamics were investigated using atomic force microscopy on monocrystalline $\mathrm{P}\mathrm{b}\mathrm{(}\mathrm{Z}{\mathrm{r}}_{\mathrm{0.2}}\mathrm{T}{\mathrm{i}}_{\mathrm{0.8}}\mathrm{)}{\mathrm{O}}_{\mathrm{3}}$ thin films. Measurements of domain size versus writing time reveal a two-step domain growth mechanism, in which initial nucleation is followed by radial domain wall motion perpendicular to the polarization direction. The electric field dependence of the domain wall velocity demonstrates that domain wall motion in ferroelectric thin films is a creep process, with the critical exponent $\ensuremath{\mu}$ close to 1. The dimensionality of the films suggests that disorder is at the origin of the observed creep behavior.
TL;DR: In this article, high-resolution transmission electron microscopy analyses reveal that the Zn core and ZnO sheath of the coaxial nanocables have an epitaxial relationship with their longitudinal axis oriented along the 〈001〉 direction.
Abstract: The heterostructures of Zn–ZnO coaxial nanocables and ZnO nanotubes with an average diameter of 30 nm have been synthesized by simple pyrolysis of zinc acetylacetonate. High-resolution transmission electron microscopy analyses reveal that the Zn core and the ZnO sheath of the nanocables have an epitaxial relationship with their longitudinal axis oriented along the 〈001〉 direction. ZnO nanotubes with a wall thickness of 4 nm possess a single-crystal structure and appear to be the extension of the ZnO sheath of the coaxial nanocables. It is suggested that the ZnO nanotubes are formed by partial evaporation of Zn core of the Zn–ZnO coaxial nanocables.
TL;DR: In this article, the authors characterized Zn1−xCoxO (x=0.25) films grown on sapphire (0001) substrates by pulsed laser deposition using various growth conditions to investigate the growth condition dependence of properties of Co-doped ZnO films.
Abstract: We have characterized Zn1−xCoxO (x=0.25) films grown on sapphire (0001) substrates by pulsed laser deposition using various growth conditions to investigate the growth condition dependence of properties of Co-doped ZnO films. The substrate temperature (TS) was varied from 300 to 700 °C and the O2 pressure (PO2) from 10−6 to 10−1 Torr. When TS is relatively low (≲600 °C), homogeneous alloy films with a wurtzite ZnO structure are grown and predominantly paramagnetic, whereas inhomogeneous films of wurtzite ZnO phase mixed with rock-salt CoO and hexagonal Co phases form when TS is relatively high and PO2 is fairly low (≲10−5 Torr). The presence of Co clusters leads to room temperature ferromagnetism in inhomogeneous films. The temperature dependence of the magnetization for the homogeneous Zn1−xCoxO (x=0.25) films shows spin-glass behavior at low temperature and high temperature Curie–Weiss behavior with a large negative value of the Curie–Weiss temperature, indicating strong antiferromagnetic exchange coupl...
TL;DR: Using grazing-incidence x-ray diffraction and scanning tunneling microscopy (STM), this article showed that the thermal decomposition of an electronic-grade wafer of 6H-SiC after annealing at increasing temperatures TA between 1080 and 1320°C leads to the layer-by-layer growth of unconstrained, heteroepitaxial single-crystalline graphite.
Abstract: Using grazing-incidence x-ray diffraction and scanning tunneling microscopy (STM), we show that the thermal decomposition of an electronic-grade wafer of 6H-SiC after annealing at increasing temperatures TA between 1080 and 1320 °C leads to the layer-by-layer growth of unconstrained, heteroepitaxial single-crystalline graphite. The limited width of the in-plane diffraction rod profiles of graphite reveals large terraces, with an average size larger than 200 A and a very small azimuthal disorientation. The overlayer is unstrained and adopts the crystalline parameter of bulk graphite even at the smallest coverage studied, which corresponds to a single graphene plane, as inferred from the flat out-of-plane diffraction profile. By increasing TA, additional graphene planes can be grown below this graphite layer from the solid-state decomposition of SiC, forming the AB stacking of Bernal graphite. A C-rich precursor is evidenced in STM by an intrinsic (6×6) reconstruction made of ordered ring or starlike structures. The resulting epitaxial film is indistinguishable from a bulk graphite single crystal.
TL;DR: In this article, structural, optical and magnetic properties of high quality epitaxial Zn 1− x Mn x O (diluted magnetic semiconductor) films were investigated using a pulsed laser deposition technique.
TL;DR: In this article, an oxide-diluted magnetic semiconductor with rutile structure, Mn-doped SnO2, has been fabricated by pulsed-laser deposition.
Abstract: Epitaxial films of an oxide-diluted magnetic semiconductor with rutile structure, Mn-doped SnO2, have been fabricated by pulsed-laser deposition. As the Mn content increases, systematic changes in lattice constants and in-gap absorption are observed. Magnetization measurements show almost paramagnetic behavior. The injection of n-type carrier over 1020 cm−3 is achieved by Sb doping. A Sn0.95Mn0.05O2:Sb film shows giant positive magnetoresistance as large as 60% at 5 K.
TL;DR: In this article, a freestanding GaN substrate of over 2-inch size with low dislocation density was prepared by hydride vapor phase epitaxy (HVPE) using GaAs (1.1)A as a starting substrate.
TL;DR: In this article, the size distribution of ordered gallium arsenide (GaAs) wires is drastically narrowed by depositing the gold catalyst through an NCA template mask, which narrows the size distributions of the gold dots and arranges them in a well-ordered array.
Abstract: Ordered gallium arsenide (GaAs) nanowires are grown by molecular-beam epitaxy on GaAs (111)B substrates using Au-catalyzed vapor–liquid–solid growth defined by nanochannel alumina (NCA) templates. Field-emission scanning electron microscope images show highly ordered nanowires with a growth direction perpendicular to the substrate. The size (i.e., diameter) distribution of the wires is drastically narrowed by depositing the gold catalyst through an NCA template mask; this narrows the size distribution of the gold dots and arranges them in a well-ordered array, as defined by the NCA template. The nanowire diameter distribution full width at half maximum on the masked substrate is 5.1 nm, compared with 15.7 nm on an unmasked substrate.
TL;DR: In this article, a review on the latest developments in group-III nitride growth on Si by metal organic vapor phase epitaxy is presented. But the main problem limiting a fast progress of GaN growth on silicon is the thermal mismatch of the GaN and Si leading to cracks even below device-relevant layer thicknesses.
Abstract: Nowadays, GaN-based devices are usually grown on sapphire or silicon-carbide substrates. These are either insulating or very expensive and not available in large diameter. A well-conducting low-cost alternative is silicon also enabling the integration of optoelectronics or high-power electronics with Si-based electronics. The main problem limiting a fast progress of GaN growth on silicon is the thermal mismatch of GaN and Si leading to cracks even below device-relevant layer thicknesses. In the last few years, since the first demonstration of a molecular beam epitaxy grown GaN-based light emitting diode on Si in 1998 the activities in research of GaN on Si increased dramatically. Meanwhile, several concepts to lower stress, avoid cracks, and improve the material quality exist. Meanwhile the material quality has improved significantly and is about as good as on sapphire so that it is only a question of time until GaN-based devices on Si come into market. This article gives a review on the latest developments in group-III nitride growth on Si by metal organic vapor phase epitaxy.
TL;DR: In this article, the flatband barrier height was determined to be 0.89 and 0.92 eV by currentvoltage and capacitance-voltage measurements, respectively, and the ideality factor was found to be 1.33.
Abstract: Silver Schottky contacts were fabricated on (1120) n-ZnO epilayers, which were grown on R-plane sapphire substrates by metalorganic chemical-vapor deposition. The flatband barrier height was determined to be 0.89 and 0.92 eV by current–voltage and capacitance–voltage measurements, respectively. The ideality factor was found to be 1.33.
TL;DR: In this paper, the structural, electrical and optical properties of a single-crystal aluminum-doped zinc oxide (AZO) film were investigated as a function of substrate deposition temperature and background gas pressure.
TL;DR: In this article, the spin-injection efficiency of 6% at the MnAs/GaAs interface is estimated on the basis of spin-relaxation times extracted from time-resolved photoluminescence measurements.
Abstract: The spin injection into GaAs has been studied for the ferromagnetic metal MnAs. Evidence for preferential minority-spin injection is obtained from the circular polarization of the electroluminescence in GaAs/(In,Ga)As light-emitting diodes (LED). The spin-injection efficiency of 6% at the MnAs/GaAs interface is estimated on the basis of spin-relaxation times extracted from time-resolved photoluminescence measurements. This efficiency, as well as the preferential spin orientation, resembles very much the injection behavior found for epitaxial Fe layers. The results do not depend on the azimuthal orientation of the epitaxial MnAs injection layer.
TL;DR: In this paper, the photoluminescence spectra of ZnO films grown by low pressure metalorganic vapor phase epitaxy (MOPE) were analyzed at 10 K and at room temperature.
Abstract: We report on photoluminescence (PL) spectra of ZnO films grown by low pressure metalorganic vapor phase epitaxy. For PL measurements, high quality ZnO thin films were epitaxially grown on Al2O3(0001) substrates. Time-integrated PL spectra of the films at 10 K clearly exhibited free A and B excitons at 3.376 and 3.382 eV and bound exciton peaks at 3.360, 3.364, and 3.367 eV. With increasing temperature, intensities of the bound exciton peaks drastically decreased and a free exciton peak was dominant above 40 K. Furthermore, time-resolved PL measurements at the free exciton peak were carried out at room temperature. The decay profiles were of double-exponential form, and the decay time constants of 180 ps and 1.0 ns were obtained using a least-square fit of the data.
TL;DR: In this paper, the surface coverage during the growth of GaN by plasma-assisted molecular-beam epitaxy (PAMBE) has been systematically studied by reflection high-energy electron diffraction as a function of the Ga flux and the substrate temperature.
Abstract: The Ga surface coverage during the growth of GaN by plasma-assisted molecular-beam epitaxy (PAMBE) has been systematically studied by reflection high-energy electron diffraction as a function of the Ga flux and the substrate temperature. As a consequence, a diagram is depicted, which describes the Ga surface coverage during PAMBE as function of growth conditions. In particular, we show that a region exists in this diagram, in which the Ga surface coverage is independent of fluctuations in the Ga flux or the substrate temperature and which forms a “growth window” for GaN growth. The influence of the Ga surface coverage on the GaN surface morphology and the growth kinetics is discussed.
TL;DR: In this article, high-quality Ga-doped n-type ZnO epilayers were grown on a plane sapphire substrates by molecular beam epitaxy (MBE) at various Ga cell temperatures from 350°C to 450°C.
TL;DR: In this article, the first report of room-temperature ferromagnetic behavior in diluted magnetic semiconductor (DMS) GaGdN ternary alloy was presented.
TL;DR: The characteristics of GaAs1-xBix semiconductor alloy layers grown by metalorganic vapor phase epitaxy (MOVPE) have been studied in this article, which supports the hypothesis that III-V alloy semiconductors consisting of semiconductor and semimetal components have a temperatureinsensitive band gap.
Abstract: The characteristics of GaAs1-xBix semiconductor alloy layers grown by metalorganic vapor phase epitaxy (MOVPE) have been studied GaAs1-xBix epilayers were obtained on GaAs substrates The lattice constants of the alloy were found to increase with the addition of Bi The uniformity and the reproducibility of the solid composition of the GaAs1-xBix epilayers are good in spite of the difficulty of epitaxial growth Although layer growth was performed at a low temperature (365°C), the stability of GaAs1-xBix alloy was sufficient for device processing, which was demonstrated by annealing in an arsenic atmosphere at 560°C for 30 min The photoluminescence (PL) spectra show that the PL peak energy of the GaAs1-xBix alloy shifts to a longer wavelength with increasing Bi content The temperature dependence of the PL peak energy is much weaker than the temperature variation of the band gap of GaAs; the temperature dependence of the PL peak energy of the GaAs0974Bi0026 layer is less than one-third the temperature variation of the band gap of GaAs The results obtained in this research support the hypothesis that III–V alloy semiconductors consisting of semiconductor and semimetal components have a temperature-insensitive band gap
TL;DR: The critical aspects of the epitaxial growth of alkaline-earth oxides on silicon are described in detail in this paper, with emphasis placed on the favorable interface stability, oxidation, structural, and strain considerations for each stage of the growth via molecular beam epitaxy.
Abstract: The critical aspects of the epitaxial growth of alkaline-earth oxides on silicon are described in detail. The step by step transition from the silicon to the alkaline-earth oxide as shown through reflection high energy electron diffraction is presented, with emphasis placed on the favorable interface stability, oxidation, structural, and strain considerations for each stage of the growth via molecular beam epitaxy.
TL;DR: In this article, the authors investigated the growth and materials properties of pure and Co-doped TiO2 anatase on SrTiO3(001) and LaAlO3 (001), grown by oxygen plasma assisted molecular beam epitaxy.