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Showing papers on "Epitaxy published in 2001"


Journal ArticleDOI
08 Jun 2001-Science
TL;DR: The realization of an ultraviolet light–emitting diode with the use of a diamond pn junction was reported, and at forward bias of about 20 volts strong ultraviolet light emission at 235 nanometers was observed and was attributed to free exciton recombination.
Abstract: We report the realization of an ultraviolet light–emitting diode with the use of a diamond pn junction. The pn junction was formed from a boron-doped p-type diamond layer and phosphorus-doped n-type diamond layer grown epitaxially on the {111} surface of single crystalline diamond. The pn junction exhibited good diode characteristics, and at forward bias of about 20 volts strong ultraviolet light emission at 235 nanometers was observed and was attributed to free exciton recombination.

515 citations


Journal ArticleDOI
TL;DR: In this paper, the role of epitaxy in molecular organization on crystalline substrates is described and a much-needed grammar is presented that classifies the various modes of epitaxial formation according to transformation matrices that relate the overlayer lattice to the substrate lattice.
Abstract: The recent emergence of molecular films as candidates for functional electronic materials has prompted numerous investigations of the underlying mechanisms responsible for their structure and formation. This review describes the role of epitaxy in molecular organization on crystalline substrates. A much-needed grammar of epitaxy is presented that classifies the various modes of epitaxy according to transformation matrices that relate the overlayer lattice to the substrate lattice. The different modes of epitaxy can be organized hierarchically to reflect the balance of overlayer–substrate and molecule–molecule energies. In the case of molecular overlayers, the mismatch of overlayer and substrate symmetries commonly leads to coincident epitaxy in which some of the overlayer lattice points do not reside on substrate lattice points. Analyses of numerous reported epitaxial molecular films reveal that coincidence is quite common even though, based on overlayer–substrate interface energies alone, not as energetically favorable as commensurism. The prevalence of coincidence can be attributed to overlayer elastic constants, associated with molecule–molecule interactions within the overlayer, that are larger than the elastic constants of the overlayer–substrate interface. This condition facilitates prediction of the epitaxial configuration and overlayer structure through simple and comparatively efficient geometric modeling that does not require the input of potential energies, while revealing the role of phase coherence between the overlayer and substrate lattices.

463 citations


Journal ArticleDOI
TL;DR: In this paper, p-type conducting CuGaO2 thin films were prepared on α-Al2O3 (001) single-crystal substrates by pulsed laser deposition.
Abstract: Transparent p-type conducting CuGaO2 thin films were prepared on α-Al2O3 (001) single-crystal substrates by pulsed laser deposition. The films were grown epitaxially on the substrates in an as-deposited state. X-ray pole figure analysis revealed that the films were composed of two types of epitaxial grains, both with c axes oriented perpendicular to the surface and a axes rotated 60° with respect to each other around the c axis. Observation of the CuGaO2 thin films by atomic force microscopy and high-resolution transmission electron microscopy substantiated this conclusion. The films have high optical transparency (∼80%) in the visible region, and the energy gap of CuGaO2 for direct allowed transition was estimated to be 3.6 eV. p-type conductivity was confirmed by Seebeck and Hall measurements. The electrical conductivity, carrier (positive hole) density, and Hall mobility of the films at room temperature were 6.3×10−2 S cm−1, 1.7×1018 cm−3, and 0.23 cm2 V−1 s−1, respectively.

401 citations


Journal ArticleDOI
TL;DR: In this paper, high quality Zn1−xMgxO(0.49) thin films were epitaxially grown at 500-650°C on Al2O3(00⋅1) substrates using metalorganic vapor-phase epitaxy.
Abstract: High-quality Zn1−xMgxO(0.00⩽x⩽0.49) thin films were epitaxially grown at 500–650 °C on Al2O3(00⋅1) substrates using metalorganic vapor-phase epitaxy. By increasing the Mg content in the films up to 49 at. %, the c-axis constant of the films decreased from 5.21 to 5.14 A and no significant phase separation was observed as determined by x-ray diffraction measurements. Furthermore, the near-band-edge emission peak position showed blueshifts of 100, 440, and 685 meV at Mg content levels of 9, 29, and 49 at. %, respectively. Photoluminescent properties of the alloy films are also discussed.

380 citations


Journal ArticleDOI
TL;DR: In this paper, a patterned sapphire substrate (PSS) with parallel grooves along the SA direction was fabricated by standard photolithography and subsequent reactive ion etching (RIE).
Abstract: Ultraviolet (UV) light-emitting diodes (LEDs) with an InGaN multi-quantum-well (MQW) structure were fabricated on a patterned sapphire substrate (PSS) using a single growth process of metalorganic vapor phase epitaxy. In this study, the PSS with parallel grooves along the sapphire direction was fabricated by standard photolithography and subsequent reactive ion etching (RIE). The GaN layer grown by lateral epitaxy on a patterned substrate (LEPS) has a dislocation density of 1.5×108 cm-2. The LEPS-UV-LED chips were mounted on the Si bases in a flip-chip bonding arrangement. When the LEPS-UV-LED was operated at a forward-bias current of 20 mA at room temperature, the emission wavelength, the output power and the external quantum efficiency were estimated to be 382 nm, 15.6 mW and 24%, respectively. With increasing forward-bias current, the output power increased linearly and was estimated to be approximately 38 mW at 50 mA.

370 citations


Journal ArticleDOI
TL;DR: In this article, the authors achieved a maximum conductivity of 42'000 S/cm with mobility of 609 cm2/V's when the CdO epitaxial film was doped with 2.5% Sn.
Abstract: Epitaxial growth of both pure and doped CdO thin films has been achieved on MgO (111) substrates using pulsed laser deposition. A maximum conductivity of 42 000 S/cm with mobility of 609 cm2/V s is achieved when the CdO epitaxial film is doped with 2.5% Sn. The pure CdO epitaxial film has a band gap of 2.4 eV. The band gap increases with doping and reaches a maximum of 2.87 eV when the doping level is 6.2%. Both grain boundary scattering and ionized impurity scattering are found to contribute to the mobility of CdO films.

335 citations


Journal ArticleDOI
TL;DR: In this paper, a freestanding GaN substrate over 2 inches in size was successfully prepared for the first time by hydride vapor phase epitaxy (HVPE) using GaAs as a starting substrate.
Abstract: A freestanding GaN substrate over 2 inches in size was successfully prepared for the first time by hydride vapor phase epitaxy (HVPE) using GaAs as a starting substrate. In the experiment, a GaAs (111)A substrate with a SiO2 mask pattern on its surface was used. A thick GaN layer was grown on the GaAs substrate at 1030°C through the openings in the SiO2 mask. By dissolving the GaAs substrate in aqua regia, a freestanding GaN substrate about 500 µm thick was obtained. The full-width at half maximum (FWHM) in the ω-mode X-ray diffraction (XRD) profile of GaN (0002) plane was 106 arcsec. The dislocation density of the GaN substrate obtained was determined to be as low as 2×105 cm-2 by plan-view transmission electron microscopy (TEM). Hall measurements revealed the n-type conductivity of the GaN substrate with typical carrier concentration and carrier mobility of 5×1018 cm-3 and 170 cm2V-1s-1, respectively.

332 citations


Journal ArticleDOI
TL;DR: In this article, the insertion of AlN/GaN superlattices was found to decrease the stress sufficiently for avoiding crack formation in an overgrown (2.5 μm) GaN layer.
Abstract: The strain in GaN epitaxial layers grown on silicon (111) substrates by metalorganic vapor phase epitaxy has been investigated. The insertion of AlN/GaN superlattices was found to decrease the stress sufficiently for avoiding crack formation in an overgrown thick (2.5 μm) GaN layer. X-ray diffraction and photoluminescence measurements are used to determine the effect of these AlN/GaN superlattices on the strain in the subsequent GaN layers. A reduction of threading dislocation density is also observed by transmission electron microscopy and atomic force microscopy when such superlattices are used. Strong band edge photoluminescence of GaN on Si(111) was observed with a full width at half maximum of the bound exciton line as low as 6 meV at 10 K. The 500 arcsec linewidth on the (002) x-ray rocking curve also attests the high crystalline quality of GaN on Si (111), when using these AlN/GaN superlattices.

275 citations


Journal ArticleDOI
TL;DR: In this paper, the two deep traps responsible for current collapse in AlGaN/GaN high electron mobility transistors grown by metalorganic vapor phase epitaxy have been studied by photoionization spectroscopy.
Abstract: The two deep traps responsible for current collapse in AlGaN/GaN high electron mobility transistors grown by metalorganic vapor-phase epitaxy have been studied by photoionization spectroscopy. Varying the growth pressure of the high resistivity GaN buffer layer results in a change in the deep trap incorporation that is reflected in the observed current collapse. Variations in the measured trap concentrations with growth pressure and carbon incorporation indicate that the deepest trap is a carbon-related defect, while the mid-gap trap may be associated with grain boundaries or dislocations.

275 citations


Journal ArticleDOI
TL;DR: Orientation-patterned GaAs (OPGaAs) films of 200 μm thickness have been grown by hydride vapor phase epitaxy (HVPE) on an orientation patterned template fabricated by molecular beam epitaxy as discussed by the authors.
Abstract: Orientation-patterned GaAs (OPGaAs) films of 200 μm thickness have been grown by hydride vapor phase epitaxy (HVPE) on an orientation-patterned template fabricated by molecular beam epitaxy (MBE). Fabrication of the templates utilized only MBE and chemical etching, taking advantage of GaAs/Ge/GaAs heteroepitaxy to control the crystal orientation of the top GaAs film relative to the substrate. Antiphase domain boundaries were observed to propagate vertically under HVPE growth conditions so that the domain duty cycle was preserved through the thick GaAs for all domain periods attempted. Quasiphase-matched frequency doubling of a CO2 laser was demonstrated with the beam confocally focused through a 4.6 mm long OPGaAs film.

256 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe a method to fabricate multilayer colloidal crystals formed by the layer-by-layer deposition of silica beads on a glass substrate, where each layer of the crystal consists of a three-dimensionalally ordered array of close-packed colloids.
Abstract: This communication describes a method to fabricate multilayer colloidal crystals formed by the layer-by-layer deposition of silica beads on a glass substrate. Each layer of the crystal consists of a three-dimensionally ordered array of close-packed colloids. These multilayer samples are amenable to templating methods for tuning the dielectric contrast of the material. The resulting photonic crystal structures exhibit optical properties which resemble the superposition of the properties of each individual crystal, with additional structure that suggests the onset of superlattice-type miniband formation. These multilayer structures thus afford new opportunities for engineered photonic behavior. Traditionally colloidal crystals are three dimensional periodic structures formed from monodisperse colloids. Because of their diffractive optical properties they are a type of photonic crystal and may have applications as optical filters and switches, high density magnetic data storage devices, chemical and biochemical sensors, or as removable scaffolds for the formation of highly ordered, macroporous materials. They are also useful as model systems for fundamental studies of crystal melting and phase transition behavior. The process of colloidal crystallization has been extensively studied, leading to the development of several methods to make high quality colloidal crystals with few crystalline defects. These techniques include electrostatically induced crystallization, gravity sedimentation, electro-hydrodynamic deposition, colloidal epitaxy, physical confinement and convective self-assembly. Bimodal AB2 and AB13 colloidal crystals with complex structures have also been observed in binary mixtures of hard-sphere colloids with specific radii ratios. Here we report a method to make a new form of colloidal crystal, a multilayer crystal, using successive deposition of crystals of colloids of arbitrary sizes. The multilayer colloidal crystal is schematically represented in Figure 1A. Spheres of different colors represent submicrometer silica or polystyrene colloids of different sizes. Each layer of the crystal is a close-packed array of colloids, and the overall structure consists of successively stacked crystals, formed of colloids of arbitrary diameters. The preparation of these structures is described in the experimental section. The high uniformity of the resulting crystals can be illustrated by the transmission (Fig. 1B) and reflection (Fig. 1C and D from different angles) photographs of a threelayer crystal. This sample is formed by consecutive deposition of 13 layers of 430 nm silica spheres, followed by 16 layers of 253 nm silica spheres, followed by 10 layers of 338 nm silica spheres. We describe the multilayer colloidal crystal pattern by listing the sphere size from bottom to top. For example, the sample in Figure 1 is referred to as 430 nm/253 nm/338 nm. The reflected colors are caused by Bragg diffraction of visible light by the three-dimensionally ordered arrays of submicrometer colloids. When two overlapping layers are made from colloids with extremely different sizes, most of the reflected light from the bottom layer will transmit through the upper layer, resulting in the transparent appearance of the second layer in Figure 1C (430 nm/253 nm). Crystalline quality is among the most important parameters in determining the performance of colloidal crystals in optical applications. Figure 2 shows the typical top-view and crosssectional scanning electron microscopy (SEM) images of each astepo of the sample shown in Figure 1. In Figure 2A, the hexagonal close-packed (hcp) arrangement of the top 430 nm layer is evident. The sharp peaks in the two-dimensional fast Fourier transform (FFT, inset) of a low-magnification image confirm the presence of long-range crystalline order extending over the largest length scales (40 ” 40 lm) accessible in a single image. The stacking of close-packed layers shown in Figure 2B demonstrates the high degree of order along the (111) crystallographic axis, perpendicular to the substrate.

Patent
10 Aug 2001
TL;DR: In this paper, the lattice constant of GaAs is close to that of Ge, GaAs has high quality with limited dislocation defects, and the relaxed GaAs layer is bonded to a second oxidized substrate.
Abstract: A process for producing monocrystalline semiconductor layers. In an exemplary embodiment, a graded SIl-xGex(x increases from 0 to y) is deposited on a first silicone substrate, followed by deposition of a relaxed Sil-yGey layer, a thin strained Sil-zGez layer. Hydrogen ions are then introduced into the strained SizGez layer. The relaxed Sil-yGey layer is bonded to a second oxidized substrate. An annealing treatment splits the bonded pair at the strained Si layer, such that the second relaxed Sil-yGey layer remains on the second substrate. In another exemplary embodiment, a graded Sil-xGex is deposited on a first silicon substrate, where the Ge concentration x is increased from 0 to 1. Then a relaxed GaAs layer is deposited on the relaxed Ge buffer. As the lattice constant of GaAs is close to that of Ge, GaAs has high quality with limited dislocation defects. Hydrogen ions are introduced into the relaxed GaAs layer at the selected depth. The relaxed GaAs layer is bonded to a second oxidized substrate. An annealing treatment splits the bonded pair at the hydrogen ion rich layer, such that the upper portion of relaxed GaAs layer remains on the second substrate.

Patent
12 Mar 2001
TL;DR: In this article, a Group III-V nitride boule is formed by growing a group III-v nitride material on a corresponding native Group III V nitride seed crystal by vapor phase epitaxy at a growth rate above 20 micrometers per hour.
Abstract: A boule formed by high rate vapor phase growth of Group III-V nitride boules (ingots) on native nitride seeds (Figure 1), from which wafers may be derived for fabrication of microelectronic structures (Figure 5). The boule is of microelectronic device quality, e.g., having a transverse dimension greater than 1 centimeter, a length greater than 1 millimeter, and a top surface defect density of less than 107 defects cm-2. The Group III-V nitride boule may be formed by growing a Group III-V nitride material on a corresponding native Group III-V nitride seed crystal by vapor phase epitaxy at a growth rate above 20 micrometers per hour.

Patent
14 Aug 2001
TL;DR: In this article, a single crystal M*N article is made by a process including the steps of: providing a substrate of material having a crystalline surface which is epitaxially compatible with M *N; depositing a layer of single crystal m*N over the surface of the substrate; and removing the substrate from the layer of M * N, e.g., with an etching agent which is applied to the substrate to remove same.
Abstract: A single crystal M*N article, which may be made by a process including the steps of: providing a substrate of material having a crystalline surface which is epitaxially compatible with M*N; depositing a layer of single crystal M*N over the surface of the substrate; and removing the substrate from the layer of single crystal M*N, e.g., with an etching agent which is applied to the substrate to remove same, to yield the layer of single crystal M*N as said single crystal M*N article. The bulk single crystal M*N article is suitable for use as a substrate for the fabrication of microelectronic structures thereon, to produce microelectronic devices comprising bulk single crystal M*N substrates, or precursor structures thereof.

Journal ArticleDOI
TL;DR: In this article, a Co-doped TiO2 target was used to produce a single phase of rutile film with the concentration of Co between 0 and 5% and the magnetic hysteresis could also be observed even at room temperature with a magnetic moment of 1 µB/Co atom.
Abstract: Epitaxial TiO2 rutile films were fabricated on α-Al2O3 (1012) substrate in the layer-by-layer fashion by laser molecular beam epitaxy. Ablation with a Co-doped TiO2 target produced single phase of rutile film with the concentration of Co between 0 and 5%. Some ferromagnetic domain structures were observed in CoxTi1-xO2 rutile films by a scanning superconducting quantum interference device microscope at 3 to 90 K. The magnetic hysteresis could also be observed even at room temperature with a magnetic moment of ~ 1 µB/Co atom.

Journal ArticleDOI
TL;DR: In this article, a single nano-sized graphene sheet is prepared by a combination of electrophoretic deposition (EPD) and heat-treatment of diamond nano-particles on a highly oriented pyrolytic graphite (HOPG) substrate.

Patent
27 Jun 2001
TL;DR: In this paper, the authors describe a III-V nitride homoepitaxial microelectronic device structure comprising a 3-v nitride epi layer on a substrate, e.g., of freestanding character.
Abstract: A III-V nitride homoepitaxial microelectronic device structure comprising a III-V nitride homoepitaxial epi layer on a III-V nitride material substrate, e.g., of freestanding character. Various processing techniques are described, including a method of forming a III-V nitride homoepitaxial layer on a corresponding III-V nitride material substrate, by depositing the III-V nitride homoepitaxial layer by a VPE process using Group III source material and nitrogen source material under process conditions including V/III ratio in a range of from about 1 to about 105, nitrogen source material partial pressure in a range of from about 1 to about 103 torr, growth temperature in a range of from about 500 to about 1250 degrees Celsius, and growth rate in a range of from about 0.1 to about 500 microns per hour. The III-V nitride homoepitaxial microelectronic device structures are usefully employed in device applications such as UV LEDs, high electron mobility transistors, and the like.

Patent
20 Nov 2001
TL;DR: In this article, a gate electrode is formed on a semiconductor substrate with a gate insulating film interposed therebetween, and a sidewall spacer is then formed at the lateral sides of the gate electrode.
Abstract: A gate electrode is formed on a semiconductor substrate with a gate insulating film interposed therebetween, and a sidewall spacer is then formed at the lateral sides of the gate electrode on the semiconductor substrate. Epitaxial growth is conducted at a lower growth rate to form, at both lateral sides of the sidewall spacer on the semiconductor substrate, first semiconductor layers made of first single-crystal silicon films superior in crystallinity. Then, epitaxial growth is conducted at a higher growth rate to form, on the first semiconductor layers, second semiconductor layers made of single-crystal films or polycrystalline films, which are inferior in crystallinity, or amorphous films. The upper areas of the first semiconductor layers and the whole areas of the second semiconductor layers are doped with impurity, thus forming impurity diffusion layers respectively serving as a source and a drain.

Journal ArticleDOI
TL;DR: In this article, the surface passivation process of GaN utilizing SiNx film by electron-cyclotron-resonance assisted plasma chemical vapor deposition (ECR-CVD) achieved low interface state density, 2×1011cm−2'eV−1.
Abstract: Chemical and electrical properties of the surfaces of GaN and GaN/AlGaN heterostructures were systematically investigated by x-ray photoelectron spectroscopy (XPS), capacitance–voltage, and current–voltage measurements. From in situ XPS study, relatively smaller band bending of 0.6 eV was seen at the GaN (2×2) surface grown by radio frequency-assisted molecular beam epitaxy on the metalorganic vapor phase epitaxy GaN template. After exposing the sample surface to air, strong band bending took place at the surface. The surface treatment in NH4OH solution and N2 plasma was found to reduce the surface Fermi level pinning. Surface passivation process of GaN utilizing SiNx film by electron-cyclotron-resonance assisted plasma chemical vapor deposition (ECR–CVD) achieved low interface state density, 2×1011cm−2 eV−1. No pronounced stress remained at the SiNx/GaN interface, which was confirmed by Raman spectroscopy. The present NH4OH/ECR–N2 plasma treatment was also found to be effective in realizing well-ordered ...

Journal ArticleDOI
TL;DR: In this article, an anatase thin films were fabricated on lattice-matched (−0.2%) LaAlO3 (001) substrates by laser molecular-beam epitaxy.
Abstract: Epitaxial anatase thin films were fabricated on lattice-matched (−0.2%) LaAlO3 (001) substrates in the layer-by-layer fashion by laser molecular-beam epitaxy. X-ray diffraction and transmission electron microscope show the films to exhibit high crystallinity and atomically defined interfaces. By virtue of the adoption of LaAlO3 substrate, which is transparent to photoexcitation of TiO2, optical band gaps could be determined to be 3.3 eV at room temperature. A photoluminescence band due to recombination of self-trapped excitons was observed at 5 K to give the peak maximum at 2.2 eV. As a result of the high degree of orientation of the epitaxial films, anisotropic optical absorption was clearly observed.

Journal ArticleDOI
TL;DR: Magnetic and transport properties of ferromagnetic III-V semiconductor (Ga,Mn)As, an alloy between GaAs and transition element Mn, are reviewed in this article.

Journal ArticleDOI
TL;DR: In this paper, anatase and rutile structures of TiO 2 films with a pulsed laser deposition (PLD) with a Nd/YAG laser under the controlled O 2 atmosphere were successfully prepared on different oxide substrates with different lattice parameters.

Journal ArticleDOI
TL;DR: In this article, the influence of the presence of a Ga film on the growth mode of GaN on AlN~0001! by plasma-assisted molecular-beam epitaxy is studied.
Abstract: We study the adsorption of Ga on ~0001! GaN surfaces by reflection high-energy electron diffraction. It is shown that a dynamically stable Ga bilayer can be formed on the GaN surface for appropriate Ga fluxes and substrate temperatures. The influence of the presence of this Ga film on the growth mode of GaN on AlN~0001! by plasma-assisted molecular-beam epitaxy is studied. It is demonstrated that under nearly stoichiometric and N-rich conditions, the GaN layer relaxes elastically during the first stages of epitaxy. At high temperatures the growth follows a Stranski-Krastanov mode, whereas at lower temperatures kinetically formed flat platelets are observed. Under Ga-rich conditions—where a Ga bilayer is rapidly formed due to excess Ga accumulating on the surface—the growth follows a Frank-van der Merwe layer-by-layer mode at any growth temperature and no initial elastic relaxation occurs. Hence, it is concluded that excess Ga acts as a surfactant, effectively suppressing both Stranski-Krastanov islanding and platelet formation. It is further demonstrated that the StranskiKrastanov transition is in competition with elastic relaxation by platelets, and it is only observed when relaxation by platelets is inefficient. As a result, a growth mode phase diagram is outlined for the growth of GaN on AlN~0001!.

Journal ArticleDOI
TL;DR: In this article, a gallium and nitrogen co-doped ZnO films were grown on an undoped buffer layer and X-ray diffraction measurements indicated the formation of ZnGa2O4.
Abstract: It has been recently predicted that the co-doping of an acceptor (nitrogen) and a donor (aluminum, gallium, indium) in a 2:1 ratio will dope ZnO p-type due to a reduction in the Madelung energy making the nitrogen acceptor energy level more shallow. We have been growing gallium and nitrogen co-doped ZnO films by radical-source molecular-beam epitaxy by use of oxygen and nitrogen radicals supplied via rf radical source cells. Diode-like current–voltage characteristics and donor acceptor pair-like photoluminescence emission were observed for a Ga and N doped ZnO film grown on an undoped ZnO buffer layer. However, Hall measurements revealed that the conductivity was n-type. Formation of a non-ZnO phase in the sample was confirmed by secondary ion mass spectroscopy and x-ray diffraction measurements. Zn and Zn+O secondary ion intensities fell sharply by two orders of magnitude in going from the undoped ZnO layer to the highly co-doped ZnO. X-ray diffraction measurements indicated the formation of ZnGa2O4.

Journal ArticleDOI
TL;DR: In this paper, the structural behavior and electrical transport properties of epitaxial α-SnO thin films grown on the (1012) α-Al2O3 (sapphire) substrate were studied.
Abstract: We studied the structural behavior and electrical transport properties of epitaxial α-SnO thin films grown on the (1012) α-Al2O3 (sapphire) substrate Hall effect measurements revealed that the epitaxial as-deposited SnO film is a p-type semiconductor In situ x-ray diffraction studies show that the α-SnO phase is metastable and will transform into SnO2 with the rutile type structure when annealed at high temperatures in air The onset of this phase transformation was observed to begin approximately at 300 °C during heating Shortly thereafter, rutile SnO2 was observed to coexist with α-SnO and intermediate products such as Sn and Sn3O4 After being annealed at temperatures above 600 °C, the film then fully transformed into the rutile SnO2 phase Our results show that the α-SnO to SnO2 structural transformation proceeds initially by the localized disproportionate redistribution of internal oxygen at low temperature, followed by the transformation of the remaining SnO phase and intermediate phases into Sn

Journal ArticleDOI
TL;DR: In this paper, a monolithic, dual-wavelength blue/green light emitting diode (LED) consisting of two active indium gallium nitride/gallium oxide (InGaN/GaN) multiple-quantum-well segments was designed and implemented.
Abstract: We have designed and implemented a monolithic, dual-wavelength blue/green light emitting diode (LED) consisting of two active indium gallium nitride/gallium nitride (InGaN/GaN) multiple-quantum-well segments. The segments are part of a single vertical epitaxial structure in which a p++/n++ InGaN/GaN tunnel junction is inserted between the LEDs, emitting in this proof-of-concept device at 470 nm and 535 nm, respectively. The device has been operated as a three-terminal device with independent electrical control of each LEDs to a nanosecond time scale.

Journal ArticleDOI
TL;DR: In this article, the growth of high-electron-mobility AlGaN/GaN heterostructures on silicon (111) substrates by molecular-beam epitaxy using ammonia as the nitrogen source was reported.
Abstract: We report on the growth of high-electron-mobility AlGaN/GaN heterostructures on silicon (111) substrates by molecular-beam epitaxy using ammonia as the nitrogen source. Crack-free GaN layers up to 3 μm are obtained. Their optical properties are similar to those commonly obtained for films grown on sapphire, but photoluminescence spectra indicate that GaN on Si(111) is in a tensile strain state which increases with the epitaxial layer thickness. Such uncracked GaN buffer layers grown on Si(111) have been used to achieve undoped AlGaN/GaN heterostructures having electron mobilities exceeding 1600 cm2/V s at room temperature and 7500 cm2/V s at 20 K.

Journal ArticleDOI
TL;DR: In this article, a cubic phase of Zn x Mg 1−x O alloy was synthesized for epitaxial growth on MgO (100), Si (100) and α-Al 2 O 3 (0001) substrates.

Journal ArticleDOI
TL;DR: In this article, the impact of the Ga/N ratio on the structure and electrical activity of threading dislocations in GaN films grown by molecular-beam epitaxy is reported.
Abstract: The impact of the Ga/N ratio on the structure and electrical activity of threading dislocations in GaN films grown by molecular-beam epitaxy is reported. Electrical measurements performed on samples grown under Ga-rich conditions show three orders of magnitude higher reverse bias leakage compared with those grown under Ga-lean conditions. Transmission electron microscopy (TEM) studies reveal excess Ga at the surface termination of pure screw dislocations accompanied by a change in the screw dislocation core structure in Ga-rich films. The correlation of transport and TEM results indicates that dislocation electrical activity depends sensitively on dislocation type and growth stoichiometry.

Journal ArticleDOI
TL;DR: The structural properties of high-quality (0001)ZnO/Al2O3 films grown by plasmaenhanced molecular-beam epitaxy are investigated by x-ray diffraction and transmission electron microscopy as discussed by the authors.
Abstract: The structural properties of high-quality (0001)ZnO/Al2O3 films grown by plasma-enhanced molecular-beam epitaxy are investigated by x-ray diffraction and transmission electron microscopy. The only defects encountered are threading dislocations with a density of 1010–4×1010 cm−2. Most numerous dislocations are pure-edge dislocations (Burgers vector of 1/3〈1120〉), which accommodate slight in-plane misorientations between subgrains. The oxygen polarity of these films is also established.