Showing papers on "Epitaxy published in 1996"
TL;DR: Ways to control film cracking during deposition and heat treatment and why many precursors synthesize metastable crystalline structures are discussed, and the different mechanisms that convert the polycrystalline film into a single crystal are reviewed.
Abstract: Epitaxial thin films of inorganic single crystals can be grown on single-crystal substrates with a variety of different solution chemistries. This review emphasizes chemical solution deposition, in which a solution is used to deposit a layer of precursor molecules that decompose to low-density, polycrystalline films during heating. Ways to control film cracking during deposition and heat treatment and why many precursors synthesize metastable crystalline structures are discussed, and the different mechanisms that convert the polycrystalline film into a single crystal are reviewed. Hydrothermal epitaxy, in which single crystal thin films are directly synthesized on templating substrates in an aqueous solution at temperatures <150°C, is also discussed.
408 citations
TL;DR: In this paper, the ReMnO3 (Re:rare earth) thin films were proposed as a new candidate for nonvolatile memory devices, and the dielectric properties of the epitaxial and polycrystalline YMNO3 films were almost the same.
Abstract: We have proposed ReMnO3 (Re:rare earth) thin films as a new candidate for nonvolatile memory devices. In this letter, we report on fabrication of (0001) YMnO3 films on (111)MgO, (0001)ZnO:Al/(0001) sapphire, and (111)Pt/(111)MgO using rf magnetron sputtering. We succeeded in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001) sapphire substrate, and polycrystalline films on (111)Pt/(111)MgO. The dielectric properties of the epitaxial and polycrystalline YMnO3 films are almost the same. The dielectric permittivities of both films are smaller than those reported for YMnO3 single crystal.
299 citations
TL;DR: In this paper, a two-step process consisting of the epitaxy of a homogeneous Ga1−xMnxAs layer at low temperatures using molecular beam epitaxy followed by phase separation upon annealing is described.
Abstract: Spherical MnAs ferromagnetic particles with controllable diameters (5–30 nm) are embedded in a high quality GaAs matrix. The particles are formed in a two step process consisting of the epitaxy of a homogeneous Ga1−xMnxAs layer at low temperatures using molecular beam epitaxy followed by phase separation upon annealing. During the annealing step, the excess arsenic in the as‐grown film forms magnetic MnAs precipitates with the Mn from the Ga1−xMnxAs lattice. Structural and room‐temperature magnetic properties of the heterogeneous GaAs:MnAs films are described. The magnetic MnAs rich layers can be incorporated into semiconductor heterostructures as demonstrated by growing (GaAs/AlAs) multiple quantum well structures in combination with GaAs:MnAs layers.
236 citations
TL;DR: In this article, the polarity of the lattice of bulk single GaN crystals and homoepitaxial and heteroencipitation on sapphire GaN thin films has been studied using convergent beam electron diffraction.
Abstract: The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial‐on‐sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single‐crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga‐terminated, lattice planes, whereas the rough facets correspond to the (0001), N‐terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga‐terminated orientation.
226 citations
TL;DR: A flat epitaxial silver film on a gallium arsenide [GaAs(110)] surface was synthesized in a two-step process after deposition of a critical thickness of silver at low temperature led to the formation of a dense nanocluster film.
Abstract: A flat epitaxial silver film on a gallium arsenide [GaAs(110)] surface was synthesized in a two-step process. Deposition of a critical thickness of silver at low temperature led to the formation of a dense nanocluster film. Upon annealing, all atoms rearranged themselves into an atomically flat film. This silver film has a close-packed (111) structure modulated by a "silver mean" quasi-periodic sequence. The ability to grow such epitaxial overlayers of metals on semiconductors enables the testing of theoretical models and provides a connection between metal and semiconductor technologies.
211 citations
TL;DR: In this paper, the photoluminescence properties of GaN thin films were investigated for different nitridation times, and it was found that the band edge and the yellow-band luminescences are strongly dependent on the nitridated starting surface.
Abstract: GaN layers were grown by gas‐source molecular beam epitaxy on sapphire substrates using ammonia as a nitrogen source. The nitridation of an Al2O3 surface prior to the GaN growth was followed in situ by reflection high‐energy electron diffraction. A strong variation of the surface lattice parameter was observed corresponding to the formation of an AlN relaxed layer. The nucleation of GaN on such a nitridated surface is facilitated, as checked by atomic force microscopy. Optimization of the nitridation procedure is achieved by investigating the photoluminescence properties of GaN thin films grown for different nitridation times. It is found that the band‐edge and the yellow‐band luminescences are strongly dependent on the nitridated starting surface. Finally, the optimized nitridation process is used to grow high‐quality GaN epitaxial layers.
201 citations
TL;DR: In this article, the authors used ZnO as a buffer layer for the epitaxial growth of GaN on both sapphire and SiC substrates for MBE.
Abstract: Molecular beam epitaxy (MBE) of ZnO on both sapphire and SiC substrates has been demonstrated. ZnO was used as a buffer layer for the epitaxial growth of GaN. ZnO is a wurtzite crystal with a close lattice match (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SiC, and high electron conductivity. ZnO is relatively soft compared to the nitride semiconductors and is expected to act as a compliant buffer layer. Inductively coupled radio frequency plasma sources were used to generate active beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O2 into atomic oxygen. Reflected high energy electron diffraction (RHEED) of the ZnO growth surface showed a two-dimensional growth. ZnO layers had n-type carrier concentration of 9 × 1018 cm−3 with an electron mobility of 260 cm2/V-s. Initial I-V measurements displayed ohmic behavior across the SiC/ZnO and the ZnO/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer layers also exhibited a two-dimensional growth. We have demonstrated the viability of using ZnO as a buffer layer for the MBE growth of GaN.
186 citations
TL;DR: Inversion domain boundaries (IDBs) were identified in GaN films grown on sapphire by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam electron diffraction techniques as mentioned in this paper.
Abstract: Planar defects observed in GaN films grown on (0001) sapphire have been identified as inversion domain boundaries (IDBs) by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam electron diffraction techniques. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all were found to contain IDBs. The IDBs in the MBE and HVPE films extended from the interface to the film surface and formed columnar domains that ranged in width from 3 to 20 nm in the MBE films and up to 100 nm in the HVPE films. For the films investigated, the MBE films had the highest density, and the MOCVD films had the lowest density of IDBs. The nucleation of inversion domains (IDs) may result from step‐related inhomogeneities of the GaN/sapphire interface.
185 citations
TL;DR: In this article, the oxide mediated epitaxy (OME) technique was used to grow single-crystal CoSi2 layers on Si surfaces by placing a thin layer of cobalt (1-3 nm) onto surfaces covered with a thin silicon oxide layer and annealing at 500-700 °C.
Abstract: Uniform, single‐crystal CoSi2 layers have been grown on Si by the technique of oxide mediated epitaxy (OME). Deposition of a thin layer of cobalt (1–3 nm) onto surfaces covered with a thin silicon oxide layer and annealing at 500–700 °C led to the growth of epitaxial, essentially uniform, CoSi2 layers on the (100), (110), and (111) surfaces of Si. The nucleation and growth of silicide apparently occurred subsurface, leaving the silicon oxide layer largely on the surface of the silicide after the growth. On all surfaces, thicker (10–30 nm), excellent quality, CoSi2 single‐crystal thin films have been grown by repeated growth sequences. Experimental results are presented along with a discussion on the possible roles played by the thin oxide layer in promoting the epitaxial growth of silicide.
183 citations
TL;DR: In this article, a single crystal film grown epitaxially on a substrate of comparable thickness is constrained to remain flat, and the free energy change of the system due to formation of strain-relaxing interface misfit dislocations is estimated.
Abstract: The physical system under study is a single crystal film grown epitaxially on a substrate of comparable thickness which is constrained to remain flat. In general, the layers are strained due to a mismatch in lattice parameter between the film and substrate materials. The free energy change of the system due to formation of strain‐relaxing interface misfit dislocations is estimated, and the discriminating case of zero energy change leads to a critical thickness condition on mismatch strain, film thickness, substrate thickness, and crystallographic slip orientation which is necessary for the spontaneous formation of such dislocations. The condition obtained generalizes the Matthews–Blakeslee (MB) criterion for a thin film on a thick substrate to the case of a complaint substrate/epitaxial film system, and it reduces to the MB criterion when either the film or substrate is relatively thick.
170 citations
TL;DR: In this paper, several oxide-GaAs heterostructures were fabricated using in situ multiple-chamber molecular beam epitaxy, and the oxides include SiO2, MgO, and Ga2O3, all evaporated by an electron beam method.
Abstract: Several oxide‐GaAs heterostructures were fabricated using in situ multiple‐chamber molecular beam epitaxy. The oxides include SiO2, MgO, and Ga2O3(Gd2O3), all evaporated by an electron beam method. The SiO2 and Ga2O3(Gd2O3) films are amorphous while the MgO films are crystalline and part of the films are epitaxially grown on GaAs(100). Among these heterostructures, the Ga2O3(Gd2O3)–GaAs shows a photoluminescence intensity comparable to that of Al0.45Ga0.55As–GaAs, and forms accumulation and inversion layers as measured from capacitance voltage measurement in quasistatic and high frequency modes.
TL;DR: In this paper, the incorporation efficiency of indium into InGaN epitaxial layers is strongly dependent on the growth rate of the films, and it is observed that narrow and bright band edge related luminescence was observed for inGaN films up to an indium content of 20% grown at 700 °C.
Abstract: InGaN bulk layers and single quantum wells were grown by atmospheric pressure metalorganic chemical vapor deposition on c‐plane sapphire. We have found that the incorporation efficiency of indium into InGaN epitaxial layers is strongly dependent on the growth rate of the films. Narrow and bright band edge related luminescence was observed for InGaN films up to an indium content of 20% grown at 700 °C. In0.16Ga0.84N single quantum wells with graded InxGa1−xN barriers showed intense luminescence, with an energy shift towards shorter wavelength with decreasing quantum well thickness. The photoluminescence full width at half‐maximum of the 50 A thick well was as low as 7.9 nm (59 meV) at 300 K.
TL;DR: The experimental results are compared to a theoretical calculation using a first-principle total-energy pseudopotential method within the local-density formalism and there is evidence for the existence of two shallow donors in GaN.
Abstract: We report on photoluminescence experiments on hexagonal GaN epitaxial films grown by hydride and organometallic vapor phase epitaxy on sapphire and 6H-SiC. At low temperatures we observe free and bound exciton recombinations, which allow us to establish the free-exciton binding energy and the localization energies of the excitons bound to neutral donors in undoped films. We demonstrate that the energetic positions of the excitonic recombination lines depend on the layer thickness and the substrate materials on which the layer was deposited. The influence of strain on the valence-band splittings can be quantified when observing the free-exciton transitions onto the different valence bands. The experimental results are compared to a theoretical calculation using a first-principle total-energy pseudopotential method within the local-density formalism. We present evidence for the existence of two shallow donors in GaN. One of them most likely stems from an intrinsic defect. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, a Si-doped GaN layer in comparison with an undoped layer grown under the same conditions by metalorganic vapor phase epitaxy on (11.0) Al2O3 was found to improve the layer quality.
Abstract: Transmission electron microscopy, x‐ray diffraction, low‐temperature photoluminescence, and Raman spectroscopy were applied to study stress relaxation and the dislocation structure in a Si‐doped GaN layer in comparison with an undoped layer grown under the same conditions by metalorganic vapor phase epitaxy on (11.0) Al2O3. Doping of the GaN by Si to a concentration of 3×1018 cm−3 was found to improve the layer quality. It decreases dislocation density from 5×109 (undoped layer) to 7×108 cm−2 and changes the dislocation arrangement toward a more random distribution. Both samples were shown to be under biaxial compressive stress which was slightly higher in the undoped layer. The stress results in a blue shift of the emission energy and E2 phonon peaks in the photoluminescence and Raman spectra. Thermal stress was partly relaxed by bending of threading dislocations into the basal plane. This leads to the formation of a three‐dimensional dislocation network and a strain gradient along the c axis of the layer.
TL;DR: In this article, high temperature gas phase reactions between trimethylgallium (TMG) and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor.
Abstract: High temperature gas phase reactions between trimethylgallium (TMG) and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure, and reaction time were chosen to emulate the gas phase environment typical of the metal–organic vapor phase epitaxy (MOVPE) of GaN. The main gas phase species is [(CH 3)2Ga:NH2]x, where most probably x=3, resulting from the very fast adduct formation followed by elimination of methane. The further gas phase decomposition of this species proceeds through the stepwise elimination of methane. These studies indicate that little TMG exists within the growth ambient under most MOVPE growth conditions. The further gas phase reaction of [(CH3)2Ga:NH 2]x may be responsible for the strong dependence of the MOVPE GaN growth rate and uniformity commonly observed.
TL;DR: In this paper, the structure of the PTCDA on Ag(1 1 1 ) was shown to be nearly identical to that of the β-modification of the pTCDA crystals, whereas on other substrates (e.g., Ge(1 0 0 )) a disordered interface was found.
Abstract: Large and symmetric organic molecules (>200 amu) can form highly-ordered adsorbate layers and thin films when they are deposited by vacuum sublimation on clean reactive surfaces In such cases covalent bonding often occurs via the molecular π-system leading to a parallel orientation of the adsorbate as shown for oligothiophenes and PTCDA on Ag(1 1 1) A proper choice of the substrate and/or a preadsorbate may also cause an upright orientation with bonding via a reactive group of the molecule (example: NDCA/Ni(1 11)) Most of the used molecules yield long-range ordered monolayers with large, almost defect-free domains The stronger the bonding and the smaller the molecule the more likely is the formation of commensurate superstructures which indicate site-specific adsorption even for such large molecules as PTCDA or EC4T Organic epitaxy is discussed and shown for a particular system, PTCDA on Ag(1 1 1), for which the structure of the monolayer is nearly identical to that of theβ-modification of PTCDA crystals, whereas on other substrates (eg Si(1 1 1), Ge(1 0 0)) a disordered interface and hence no true epitaxy is found
TL;DR: A framework for evaluating the epitaxy of ordered organic overlayers of generic symmetry on ordered substrates is described that combines a computationally efficient method for explicit determination of the type of epitaxy and overlayer azimuthal orientation with an analysis of the elastic properties of the overlayers and the overlayer-substrate interface.
Abstract: : A framework for evaluating the epitaxy of ordered organic overlayers of generic symmetry on ordered substrates is described that combines a computationally efficient method for explicit determination of the type of epitaxy (i.e., commensurism, coincidence, or incommensurism) and overlayer azimuthal orientation with an analysis of the elastic properties of the overlayer and the overlayer-substrate interface. The azimuthal orientations predicted by this function agree with values predicted by semi-empirical potential energy calculations and observed experimentally for previously reported organic overlayers which are demonstrated here to be coincident, including electrochemically grown overlayers of molecular conductors. Calculations based on this analytical approach are much less computationally intensive than potential energy calculations as the number of computational operations is independent of the overlayer size chosen for analysis. This enables analyses to be performed for the large overlayer basis sets common for molecular overlayers. Furthermore, this facilitates the analysis of coincident overlayers, for which the overlayer size needs to be large enough to establish the phasing relationship between the substrate and large non-primitie overlays supercell so that the global minimum with respect to azimuthal angle can be determined. The computational efficiency of this method also enables convenient examination of numerous possible reconstructed overlayer configurations in which the lattice parameters are bracketed around those of the native overlayer, thereby allowing examination of possible epitaxy-driven overlayer reconstructions. When combined with calculated intralayer and overlayer-substrate elastic constants this method provides a strategy for the design of heteroepitaxial molecular films.
TL;DR: A method is presented for the determination of elastic strains from electron back scatter diffraction patterns, which are obtained at high spatial resolution, from bulk specimens in a scanning electron microscope, which offers an improvement of approximately two orders of magnitude from the more usual EBSD measurements of misorientation.
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TL;DR: In this article, an epitaxial film of the composition ZrO 2 is constructed by unidirectionally oriented crystals, which has a ten point mean roughness Rz of up to 0.60 nm across a reference length of 500 nm.
Abstract: The invention provides an oxide thin film in the form of an epitaxial film of the composition: Zr 1-x R x O 2- δ wherein R is a rare earth metal inclusive of Y, x=0 to 0.75, preferably x=0.20 to 0.50, formed on a surface of a single crystal silicon substrate. A rocking curve of the film has a half-value width of up to 1.50°. The film has a ten point mean roughness Rz of up to 0.60 nm across a reference length of 500 nm. An epitaxial film of the composition ZrO 2 is constructed by unidirectionally oriented crystals. When a functional film is to be formed on the oxide thin film serving as a buffer film, an adequately epitaxially grown functional film of quality is available. Particularly when the single crystal substrate is rotated within its plane, an oxide thin film of uniform high quality having an area as large as 10 cm 2 or more is obtained.
TL;DR: In this article, a pyramid of diamond particles with a number density of 108 cm-2 were grown on the iridium thin film by direct-current plasma chemical vapor deposition with ion irradiation pretreatment of the substrate.
Abstract: Epitaxial growth of diamond on iridium thin films was performed by direct-current plasma chemical vapor deposition with ion irradiation pretreatment of the substrate. Pyramidal epitaxial diamond particles with a number density of ~108 cm-2 were grown on the iridium film. The epitaxial relation is written as (100) diamond//(100) iridium and [001] diamond//[001] iridium. Tilting of the epitaxial relation, as occasionally observed for diamond on silicon or beta silicon carbide, is scarcely observed. Erosion,as observed for diamond on nickel substrates, is not observed. The effect of the ion irradiation of the substrate is discussed briefly.
TL;DR: In this paper, artificial superlattices consisting of antiferroelectric PbZrO3 (PZO) and PTO have been fabricated by a multi-ion beam sputtering technique.
Abstract: Artificial superlattices consisting of antiferroelectric PbZrO3 (PZO) and ferroelectric PbTiO3 (PTO) have been fabricated by a multi‐ion‐beam sputtering technique. The epitaxial PZO and PTO layers were sequentially grown on (100)Pt/MgO substrates at a low substrate temperature of 415 °C with a periodicity from 5 to 100 perovskite unit cells. X‐ray diffraction studies revealed the superlattice structures with a‐axis oriented PTO layers on a‐axis oriented PZO layers. The dielectric and ferroelectric properties of the superlattice films were enhanced with increasing periodicity.
TL;DR: In this article, the details of epitaxial growth and microstrictural characteristics of AlN films grown on sapphire (0001), (1012) and Si (100), (111) substrates were investigated using plan-view and cross-sectional high-resolution transmission electron microscopy and x-ray diffraction techniques.
Abstract: The details of epitaxial growth and microstrictural characteristics of AlN films grown on sapphire (0001), (1012) and Si (100), (111) substrates were investigated using plan‐view and cross‐sectional high‐resolution transmission electron microscopy and x‐ray diffraction techniques. The films were grown by metalorganic chemical vapor deposition using TMA1+NH3+N2 gas mixtures. Different degrees of epitaxy were observed for the films grown on α‐Al2O3 and Si substrates in different orientations. The epitaxial relationship for (0001) sapphire was found to be (0001)AlN∥(0001)sap with in‐plane orientation relationship of [0110]AlN∥[1210]sap. This is equivalent to a 30° rotation in the basal (0001) plane. For (1012) sapphire substrates, the epitaxial relationship was determined to be (1120)AlN∥(1012)sap with the in‐plane alignment of [0001]AlN∥[1011]sap. The AlN films on (0001) α‐Al2O3 were found to contain inverted domain boundaries and a/3〈1120〉 threading dislocations with the estimated density of 1010 cm−2. The density of planar defects (stacking faults) found in AlN films was considerably higher in the case of (1012) compared to (0001) substrates. Films on Si substrates were found to be highly textured c axis oriented when grown on (111) Si, and c axis textured with random in‐plane orientation on (100) Si. The role of thin‐film defects and interfaces on device fabrication is discussed.
TL;DR: In this paper, a simple molecular description for chemisorption and surface reactions is suggested and shows that both reaction steps have an effect on the growth rate of atomic layer deposition.
TL;DR: In this article, a temperature independent 2DEG mobility, indicative of the presence of a two-dimensional electron gas (2DEG), was observed in all samples below 80 K. This was attributed to the absence of significant parallel conduction paths in the material.
Abstract: High quality Al0.15Ga0.85N/GaN heterostructures have been fabricated on 6H–SiC and sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). A temperature independent mobility, indicative of the presence of a two‐dimensional electron gas (2DEG), was observed in all samples below 80 K. The highest low temperature 2DEG mobility, 7500 cm2/V s, was measured in AlGaN/GaN grown on 6H–SiC; the sheet carrier density was 6×1012 cm−2. Strong, well resolved, Shubnikov–de Haas oscillations were observed in fields as low as 3 T and persisted to temperatures as high as 15 K. Hall effect measurements also revealed the presence of well‐defined plateaus in the Hall resistance. The high quality 2DEG properties of the AlGaN/GaN heterostructures grown on 6H–SiC are attributed to the absence of significant parallel conduction paths in the material.
TL;DR: In this article, the optical properties of GaN epilayers grown by metal-organic vapor phase epitaxy on sapphire are investigated by means of photoluminescence, reflectance, and differential spectroscopy.
Abstract: The optical properties of GaN epilayers grown by metal‐organic vapor‐phase epitaxy on (0001)‐oriented sapphire are investigated by means of photoluminescence, reflectance, and differential spectroscopy. We obtain quantitative information about the intrinsic or extrinsic nature of the 2 and 300 K photoluminescence features. From detailed investigations of the reflectance properties of these layers we can quantify the residual strain field in these layers and determine the GaN deformation potentials. Comparison of these values with quantities measured on other semiconductors with wurtzite symmetry is also addressed. Last we utilize photoreflectance spectroscopy to measure exciton binding energies.
TL;DR: In this paper, a low-temperature Si buffer layer is developed to grow a SiGe epilayer with low density of dislocations on a Si substrate by molecular beam epitaxy.
Abstract: A method using a low‐temperature Si (LT‐Si) buffer layer is developed to grow a SiGe epilayer with low density of dislocations on a Si substrate by molecular‐beam epitaxy. In this method, a LT‐Si layer is used to release the stress of the SiGe layer. The samples have been investigated by x‐ray double‐crystal diffraction and transmission electron microscopy. The results indicate that the LT‐Si is effective to release the stress and suppress threading dislocations.
TL;DR: In this paper, low pressure metal organic chemical vapor deposition of single crystal, wurtzitic layers of GaN and GaN/InGaN heterostructures on (111) GaAs/Si composite substrates was reported.
Abstract: We report on the low pressure metal organic chemical vapor deposition of single crystal, wurtzitic layers of GaN and GaN/InGaN heterostructures on (111) GaAs/Si composite substrates. The structural, optical, and electrical properties of the epitaxial layers are evaluated using x‐ray diffraction, transmission electron microscopy, photoluminescence, and measurements of minority carrier diffusion length. These measurements demonstrate high quality of GaN grown on the composite substrate.
TL;DR: In this article, a planar interface between substrate and epilayer was shown to have small Ga inclusions, and the epilayers consists of less than 108 dislocations per cm2, mostly in the form of dislocation loops, which originate at the interface.
Abstract: Bulk single crystals of GaN were used for epitaxial growth of GaN by metalorganic chemical vapor deposition. Photoluminescence (at 2 K) from polished substrates yields a broad near‐band‐edge emission band centered at 3.32 eV and the commonly observed yellow luminescence band. In contrast, the epitaxial layer displays a strong, sharp bound exciton line at 3.458 eV and a weak yellow band. Transmission electron microscopy reveals a sharp, planar interface between substrate and epilayer: The substrate contains small Ga inclusions, and the epilayer consists of less than 108 dislocations per cm2, mostly in the form of dislocation loops, which originate at the interface.
TL;DR: The magnetic properties of the NiFe2O4 films are strongly affected by the structural changes; unannealed films are not magnetically saturated even in an applied field of 55 kOe, while the annealed films have properties comparable to those of bulk, single crystal NiFe 2O4.
Abstract: Thin films of NiFe2O4 were deposited on SrTiO3 (001) and Y0.15Zr0.85O2 (yttria-stabilized zirconia) (001) and (011) substrates by 90°-off-axis sputtering. Ion channeling, x-ray diffraction, and transmission electron microscopy studies reveal that films grown at 600 °C consist of ∼300 A diameter grains separated by thin regions of highly defective or amorphous material. The development of this microstructure is attributed to the presence of rotated or displaced crystallographic domains and is comparable to that observed in other materials grown on mismatched substrates (e.g., GaAs/Si or Ba2YCu3O7/MgO). Postdeposition annealing at 1000 °C yields films that are essentially single crystal. The magnetic properties of the films are strongly affected by the structural changes; unannealed films are not magnetically saturated even in an applied field of 55 kOe, while the annealed films have properties comparable to those of bulk, single crystal NiFe2O4. Homoepitaxial films grown at 400 °C also are essentially single crystal.
TL;DR: In this article, free-standing GaAs InAs heterostructure wires as thin as 20 nm and as long as 1 μm have been formed by vapor-liquid-solid (VLS) growth during organometallic vapor phase epitaxy.