Showing papers on "Epitaxy published in 2008"
TL;DR: In this article, the effect of substrate on the atomic/electronic structures of monolayer graphene is investigated and it is shown that the Raman features are independent of the substrate used.
Abstract: Graphene has attracted a lot of interest for fundamental studies as well as for potential applications. Till now, micromechanical cleavage (MC) of graphite has been used to produce high-quality graphene sheets on different substrates. Clear understanding of the substrate effect is important for the potential device fabrication of graphene. Here we report the results of the Raman studies of micromechanically cleaved monolayer graphene on standard SiO2 (300 nm)/Si, single crystal quartz, Si, glass, polydimethylsiloxane (PDMS), and NiFe. Our data suggests that the Raman features of monolayer graphene are independent of the substrate used; in other words, the effect of substrate on the atomic/electronic structures of graphene is negligible for graphene made by MC. On the other hand, epitaxial monolayer graphene (EMG) on SiC substrate is also investigated. Significant blueshift of Raman bands is observed, which is attributed to the interaction of the graphene sheet with the substrate, resulting in the change o...
700 citations
TL;DR: In this article, a facile fabricating method has been established for large-area uniform silicon nanowires arrays, which were obtained by single crystals and epitaxial on the substrate.
Abstract: A facile fabricating method has been established for large-area uniform silicon nanowires arrays All silicon nanowires obtained were single crystals and epitaxial on the substrate Six kinds of silicon wafers with different types, surface orientations, and doping levels were utilized as starting materials With the catalysis of silver nanoparticles, room-temperature mild chemical etching was conducted in aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2) The corresponding silicon nanowires arrays with different morphologies were obtained The silicon nanowires possess the same type and same doping level of the starting wafer All nanowires on the substrate have the same orientation For instance, both (100)- and (111)-oriented p-type wafers produced silicon nanowires in the (100) direction For every kind of silicon wafer, the effect of etching conditions, such as components of etchant, temperature, and time, were systemically investigated This is an appropriate method to produce a
527 citations
TL;DR: In this paper, the α-Ga2O3 films have narrow fullwidths at half maximum (FWHMs) in their X-ray diffraction curves, for example, about 60 arcsec.
Abstract: Ga2O3 thin films of the α-phase, that is, the corundum structure (in the trigonal system), have been epitaxially obtained on sapphire (α-Al2O3) substrates, in contrast to the strong tendency of Ga2O3 to assume a heterogeneous crystal structure, that is, the β-gallia structure (in the monoclinic system) on sapphire. This result is advantageous for high-quality films and is due to the growth by mist chemical vapor deposition (CVD) at low temperatures of 430–470 °C. The α-Ga2O3 films have narrow full-widths at half maximum (FWHMs) in their X-ray diffraction rocking curves, for example, about 60 arcsec. The root mean square (RMS) roughness of the surface was as small as 1 nm. The optical band gap energy obtained was 5.3 eV, and the films were almost completely transparent in the near-ultraviolet and visible regions. The epitaxial growth of α-Ga2O3 films on sapphire is beneficial for the fabrication of oxide optical and electronic devices.
387 citations
TL;DR: To integrate vertical InAs nanowires on Si by modifying initial Si(111) surface in selective-area metal-organic vapor phase epitaxy with flow-rate modulation mode at low temperature is achieved.
Abstract: We report on control of growth directions of InAs nanowires on Si substrate. We achieved to integrate vertical InAs nanowires on Si by modifying initial Si(111) surface in selective-area metal-organic vapor phase epitaxy with flow-rate modulation mode at low temperature. Cross-sectional transmission electron microscope and Raman scattering showed that misfit dislocation with local strains were accommodated in the interface.
347 citations
TL;DR: For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations as discussed by the authors.
Abstract: BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations Four-circle x-ray diffraction reveals phase-pure, epitaxial films with ω rocking curve full width at half maximum values as narrow as 29arcsec (0008°) Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 274eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films
336 citations
TL;DR: In this paper, the Raman spectra of epitaxial graphene layers grown on 63×63 reconstructed silicon carbide surfaces during annealing at elevated temperature are presented, and a significant phonon hardening is observed.
Abstract: We present Raman spectra of epitaxial graphene layers grown on 63×63 reconstructed silicon carbide surfaces during annealing at elevated temperature. In contrast to exfoliated graphene a significant phonon hardening is observed. We ascribe that phonon hardening to a minor part to the known electron transfer from the substrate to the epitaxial layer, and mainly to mechanical strain that builds up when the sample is cooled down after annealing. Due to the larger thermal expansion coefficient of silicon carbide compared to the in-plane expansion coefficient of graphite this strain is compressive at room temperature.
328 citations
TL;DR: Using the concept of sacrificial layers and elevation of Au catalyst modulated by growth condition, this work demonstrates for the first time a large area direct transfer process for nanowires formed by a bottom-up approach that can maintain both the position and alignment.
Abstract: We report the controlled growth of planar GaAs semiconductor nanowires on (100) GaAs substrates using atmospheric pressure metalorganic chemical vapor deposition with Au as catalyst. These nanowires with uniform diameters are self-aligned in direction in the plane of (100). The dependence of planar nanowire morphology and growth rate as a function of growth temperature provides insights into the growth mechanism and identified an ideal growth window of 470 ( 10 °C for the formation of such planar geometry. Transmission electron microscopy images reveal clear epitaxial relationship with the substrate along the nanowire axial direction, and the reduction of twinning defect density by about 3 orders of magnitude compared to III-V semiconductor nanowires. In addition, using the concept of sacrificial layers and elevation of Au catalyst modulated by growth condition, we demonstrate for the first time a large area direct transfer process for nanowires formed by a bottom-up approach that can maintain both the position and alignment. The planar geometry and extremely low level of crystal imperfection along with the transferability could potentially lead to highly integrated III-V nanoelectronic and nanophotonic devices on silicon and flexible substrates.
190 citations
TL;DR: This Communication demonstrates for the first time growth of high-quality InAs/InSb heterostructure nanowires, which are extremely interesting for applications in high-speed and low-power electronics, infrared optoelectronics, quantum-transport studies, and thermoelectric power generation.
Abstract: Recently, semiconducting nanowires have attracted much interest due to their advantageous physical properties and a wide range of potential applications in electronics, optoelectronics, and biosensors. High-quality compound nanowire heterostructures have been grown using various techniques, including chemical-beam epitaxy (CBE) and metal–organic vapor-phase epitaxy (MOVPE), with both methods producing sharp interfaces. To date, most studies have concentrated on ‘‘classic’’ III–V semiconductors, such as InAs, InP, GaAs, GaP, and nitride nanowires. Antimonycontaining nanowires would extend the range of usable materials in these heterostructures and devices. InSb is the III–V semiconductor with the narrowest bandgap (0.17 eV) and the largest bulk electron mobility ( 7.7 10 cm V 1 s ); it also has a high thermoelectric figure of merit (0.6). This material is therefore extremely interesting for applications in high-speed and low-power electronics, infrared optoelectronics, quantum-transport studies, and thermoelectric power generation. Despite all of these promising advantages, very few studies on InSb nanowires have been reported. There have so far been no reports on InSb-containing nanowire heterostructures. Moreover, due to the large lattice mismatch between InAs and InSb (7%), no combination of these materials has been reported using planar growth. In this Communication, we demonstrate for the first time growth of high-quality InAs/InSb heterostructure nanowires.
183 citations
TL;DR: In this article, the Ti-mask selective-area growth (SAG) of GaN on Ti-nanohole-patterned GaN templates by rf-plasma-assisted molecular-beam epitaxy was employed to demonstrate the fabrication of regularly arranged InGaN/GaN nanocolumns.
Abstract: The Ti-mask selective-area growth (SAG) of GaN on Ti-nanohole-patterned GaN templates by rf-plasma-assisted molecular-beam epitaxy was employed to demonstrate the fabrication of regularly arranged InGaN/GaN nanocolumns. The SAG of GaN nanocolumns strongly depended on the growth temperature (Tg); at Tg below 900 °C, no SAG occurred, but above 900 °C, SAG occurred. However, an excessive increase in Tg to above 900 °C at a nitrogen flow rate (QN2) of 3.5 sccm brought about increased inhomogeneity in the nanocolumn shape. Upon reducing QN2 from 3.5 to 1 sccm, uniform nanocolumn arrays were successfully grown around the critical temperature of 900 °C.
179 citations
TL;DR: In this article, a pyramidal patterned sapphire substrate in the micro-scale (MPSS) and a polysilicon patterned nanoscale (NPSS), was used to enhance the light output power of InGaN/GaN light-emitting diodes (LEDs).
Abstract: Sapphire substrates were patterned by a chemical wet etching technique in the micro- and nanoscale to enhance the light output power of InGaN/GaN light-emitting diodes (LEDs). InGaN/GaN LEDs on a pyramidal patterned sapphire substrate in the microscale (MPSS) and pyramidal patterned sapphire substrate in the nanoscale (NPSS) were grown by metalorganic chemical vapor deposition. The characteristics of the LEDs fabricated on the MPSS and NPSS prepared by wet etching were studied and the light output powers of the LEDs fabricated on the MPSS and NPSS increased compared with that of the conventional LEDs fabricated on planar sapphire substrates. In comparison with the planar sapphire substrate, an enhancement in output power of about 29% and 48% is achieved with the MPSS and NPSS at an injection current of 20 mA, respectively. This significant enhancement is attributable to the improvement of the epitaxial quality of GaN-based epilayers and the improvement of the light extraction efficiency by patterned sapphire substrates. Additionally, the NPSS is more effective to enhance the light output power than the MPSS. (c) 2008 American Institute of Physics.
175 citations
TL;DR: In this article, the self-assembled growth of GaN nanorods on Si (111) substrates by plasma-assisted molecular beam epitaxy under nitrogen-rich conditions is investigated.
Abstract: The self-assembled growth of GaN nanorods on Si (111) substrates by plasma-assisted molecular beam epitaxy under nitrogen-rich conditions is investigated. An amorphous silicon nitride layer is formed in the initial stage of growth that prevents the formation of a GaN wetting layer. The nucleation time was found to be strongly influenced by the substrate temperature and was more than 30 min for the applied growth conditions. The observed tapering and reduced length of silicon-doped nanorods is explained by enhanced nucleation on nonpolar facets and proves Ga-adatom diffusion on nanorod sidewalls as one contribution to the axial growth. The presence of Mg leads to an increased radial growth rate with a simultaneous decrease of the nanorod length and reduces the nucleation time for high Mg concentrations.
TL;DR: In this article, a Si buffer layer was grown on an undulated Si substrate by vapour phase epitaxy, which provides due to its roughness deliberate off-orientations.
TL;DR: In this paper, a long ZnO nanorod array with good verticality and thin diameter is synthesized from a single solution by the hydrothermal route, and the critical conditions for the rod growth are obtained by changing the polyethyleneimine amount and the pH.
Abstract: A long ZnO nanorod array with good verticality and thin diameter is synthesized from a single solution by the hydrothermal route. Prior to the growth, a ZnO seed layer with the c-axis texturing and the monolayer distribution is deposited on the substrate by a modified sol−gel spin coating process. A molecule adsorption stabilization mechanism is proposed to explain the seed orientation. Factors affecting the ZnO nanorod growth are systematically investigated. The critical conditions for the rod growth are obtained by changing the polyethyleneimine amount and the pH. The results suggest that the verticality of the array depends heavily on the seed orientation. The atomic force microscopy and X-ray diffraction measurements reveal that the crystallinity and the initial strain relaxation determine the growth activation energy and the rod diameter size.
TL;DR: In this paper, the bottom BaTiO3 layer epitaxially grown on the substrate acts as a buffer layer and effectively reduces the coherent constraint in the magnetic layer arising from the substrate.
Abstract: CoFe2O4–BaTiO3 heterostructure was epitaxially grown on the (001)-SrTiO3 substrate via pulsed laser deposition, in which the bottom BaTiO3 layer epitaxially grown on the substrate acts as a buffer layer and effectively reduces the coherent constraint in the magnetic layer arising from the substrate Microstructure studies from x-ray diffraction and electron microscopies showed good coherent epitaxy thin films of the (001)-CoFe2O4 and (001)-BaTiO3 on the substrate, which exhibits simultaneously strong ferroelectric and ferromagnetic responses An obvious direct magnetoelectric coupling effect was observed in the thin films, which shows an enhancement compared to previous NiFe2O4–BaTiO3 heterostructures
TL;DR: In this article, a (100)-oriented β-Ga 2 O 3 single crystal substrate was grown by plasma-assisted molecular beam epitaxy, which exhibited clear step and terrace structures and the root-mean-square roughness of 0.5 nm in atomic force microscopy.
TL;DR: In this paper, the growth of tensile-strained Ge on relaxed InxGa1−xAs epitaxial templates by metal-organic chemical vapor deposition was investigated.
Abstract: Highly tensile-strained Ge thin films and quantum dots have the potential to be implemented for high mobility metal-oxide-semiconductor field-effect transistor channels and long-wavelength optoelectronic devices. To obtain large tensile strain, Ge has to be epitaxially grown on a material with a larger lattice constant. We report on the growth of tensile-strained Ge on relaxed InxGa1−xAs epitaxial templates by metal-organic chemical vapor deposition. To investigate the methods to achieve high quality Ge epitaxy on III–V semiconductor surfaces, we studied Ge growth on GaAs with variable surface stoichiometry by employing different surface preparation processes. Surfaces with high Ga-to-As ratio are found to be necessary to initiate defect-free Ge epitaxy on GaAs. With proper surface preparation, tensile-strained Ge was grown on relaxed InxGa1−xAs with a range of In content. Low growth temperatures between 350 and 500 °C suppress misfit dislocation formation and strain relaxation. Planar Ge thin films with ...
Abstract: A simple, non-invasive method using Raman spectroscopy for the estimation of the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is presented, enabling simultaneous determination of thickness, grain size and disorder using the spectra The attenuation of the substrate Raman signal due to the graphene overlayer is found to be dependent on the graphene film thickness deduced from X-ray photoelectron spectroscopy and transmission electron microscopy of the surfaces We explain this dependence using an absorbing overlayer model This method can be used for mapping graphene thickness over a region and is capable of estimating thickness of multilayer graphene films beyond that possible by XPS and Auger electron spectroscopy (AES)
TL;DR: In this article, a 3-in GaN layer was fabricated using hydride vapor phase epitaxy and void-assisted separation method, which showed an excellent reproducibility.
TL;DR: In this article, the phase stabilization of rhombohedral (rh-) In2O3 films on sapphire substrate deposited by metal organic chemical vapor deposition was reported, with the help of a high-temperature nucleation layer and evolutionary structural selection.
Abstract: We report on the phase stabilization of rhombohedral (rh-) In2O3 films on sapphire substrate deposited by metal organic chemical vapor deposition With the help of a high-temperature nucleation layer and evolutionary structural selection of rhombohedral phase during the growth process, stable epitaxial growth of single crystalline rh-In2O3 is achieved The mechanism of phase selective epitaxial growth is studied by means of high-resolution X-ray diffraction and transmission electron microscopy measurements Furthermore, Raman spectroscopy measurements are carried out to investigate the phonon properties of rh-In2O3 Raman-active phonon modes of rh-In2O3 are first identified
TL;DR: A detailed study on the vapour-liquid-solid growth of silicon nanowires (SiNWs) on (111)-oriented Si substrates using Au as catalytic seed material was carried out in this paper.
Abstract: We have carried out a detailed study on the vapour-liquid-solid growth of silicon nanowires (SiNWs) on (111)-oriented Si substrates using Au as catalytic seed material Arrays of individual seeds were patterned by electron-beam lithography, followed by Au evaporation and lift-off SiNWs were grown using diluted silane as precursor gas in a low-pressure chemical vapor deposition system The silane partial pressure, substrate temperature, and seed diameter were systematically varied to obtain the growth rate of the NWs and the rate of sidewall deposition Activation energies of 19kcal∕mol for the axial SiNW growth and 29kcal∕mol for the radial deposition on the SiNW surface are derived from the data SiNW growth at elevated temperatures is accompanied by significant Au surface diffusion, leading to a loss of Au from the tips of the SiNWs that depends on the layout and density of the Au seeds patterned In contrast to NWs grown from a thin-film-nucleated substrate, the deterministic patterning of identical A
TL;DR: It can be unequivocally shown that the spinel-type Co(3)O(4) phase develops, for which an excellent fit between measured and calculated LEED intensity spectra is achieved and accounting for polarity compensation of the film is interpreted.
Abstract: Cobalt oxide films were prepared by oxidation of different amounts of cobalt deposited on Ir(100)-(1 × 1), where oxygen rich conditions were applied during deposition. The resulting oxide films with thicknesses of up to about 40 A were investigated as regards their crystallographic structure and morphology, applying quantitative low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). It can be unequivocally shown that the spinel-type Co3O4 phase develops, for which an excellent fit between measured and calculated LEED intensity spectra is achieved (Pendry R-factor R = 0.124). In spite of the quadratic unit cell of the substrate the oxide films are in the polar (111) orientation. Also, the native lattice parameter of the material is assumed, i.e. there is no pseudomorphic relation to the substrate. However, by means of orientational epitaxy, one of the unit-mesh vectors of the oxide and one of those of the substrate layer are aligned, leading to two mutually orthogonal domains in the oxide. The oxide is terminated by a sublayer of cobalt ions which in the bulk were tetrahedrally coordinated Co2+ ions. There are drastic relaxations of layer spacings at and near the surface. As a consequence, the bond length between the surface terminating cobalt ions and oxygen ions below is considerably reduced, indicative of a substantial change of the ionicity of the cobalt and/or oxygen ions. This is interpreted as accounting for polarity compensation of the film, as surface reconstruction, oxygen vacancies and species adsorbed can be ruled out.
TL;DR: Transmission and scanning electron microscopy analyses of a GaAs nanowires showed that many twins developed along the [Formula: see text] B direction, suggesting that twins had something to do with the evolution of the nanowire shape from tetrahedron to hexagon.
Abstract: GaAs nanowires were selectively grown by metal–organic vapour-phase epitaxy within a SiO2 mask window pattern fabricated on a GaAs(111)B substrate surface. The nanowires were 100–3000 nm in height and 50–300 nm in diameter. The height decreased as the mask window diameter was increased or the growth temperature was increased from 700 to 800 °C. The dependence of the nanowire height on the mask window diameter was compared with a calculation, which indicated that the height was inversely proportional to the mask window diameter. This suggests that the migration of growth species on the nanowire side surface plays a major role. Tetrahedral GaAs grew at an early stage of nanowire growth but became hexagonal as the growth process continued. The calculated change in Gibbs free energy for nucleation growth of the crystals indicated that tetrahedra were energetically more favourable than hexagons. Transmission and scanning electron microscopy analyses of a GaAs nanowire showed that many twins developed along the B direction, suggesting that twins had something to do with the evolution of the nanowire shape from tetrahedron to hexagon.
TL;DR: In this article, an in situ growth study of an organic layer on a salt substrate, displaying surprisingly sharp optical transitions already at room temperature, was performed by using noncontact atomic force microscopy (AFM) and advanced potential energy calculations.
Abstract: Devices based on organic semiconductors allow novel applications, stimulating intensive research on the physicochemical characteristics of organic thin films. With true molecular electronics at the horizon, understanding of the behavior of molecules on surfaces is crucial. The interactions occurring in the thin film phase and with the substrate often lead to new electronic and optical properties. Due to the strong and wavelength-selective absorption of light by organic molecules, optical absorption spectroscopy of the organic adsorbate-substrate interface is a valuable tool to study these new properties. As measurements of light absorption by molecular (sub-) monolayers on inorganic surfaces became recently feasible, the substrate influence can now be analyzed in detail. Here we report an in situ growth study of an organic layer on a salt substrate, displaying surprisingly sharp optical transitions already at room temperature. We conclude that commensurate growth minimizes the inhomogeneous broadening in those optical spectra. Both Coulomb interactions and van der Waals-bonding between inorganic substrate and molecules lead to an unexpected formation of a quadratic structure for the first monolayer, which could be directly visualized by noncontact atomic force microscopy (AFM). Through either continued deposition or annealing, the molecules rearrange and form islands that exhibit the structure of the bulk single crystal. Advanced potential energy calculations explain this transition well. Our results clearly demonstrate the significant impact of the physical structure on the resulting physicochemical properties of molecular layers. These findings can be a starting point for further theoretical and experimental studies concerning the structure-properties-relation in molecular layers on surfaces. The molecule perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) is the drosophila of organic epitaxy: Growth on a large variety of substrates, including metal surfaces (Au, Cu, Ni), semiconductors (Si, GaAs) and insulators (KBr, mica) was investigated. On these substrates the molecule forms layered van der Waals-bonded crystals exhibiting the herringbone (HB) arrangement of PTCDA molecules similar to the bulk (102) planes of PTCDA single crystals. Exceptions are certain silver surfaces to which the molecules chemisorb. On (111)-terminated Ag-crystals the molecules arrange in the HB fashion, while on Ag(110) the PTCDA monolayer is forced into a brickwall structure. Here we report on the special growth mode of PTCDA on potassium chloride (KCl) single crystals which leads to an unusual narrowing of the room temperature optical spectra not observed so far on any other substrate. All experiments were performed in ultrahigh vacuum, to reduce environmental effects such as rearrangement of the ultrathin layers due to water adsorption. The actual growth of the film was monitored in situ with differential reflectance spectroscopy (DRS), a technique applicable even at submonolayer coverage. The growth was further elucidated by non-contact AFM and advanced potential energy calculations comprising several hundreds of molecules. Figure 1A displays the coverage-dependent DRS spectra up to the first PTCDA monolayer on KCl(100), where the signal intensifies with increasing coverage, as expected. Since we use a transparent substrate, those spectra are directly comparable to the absorbance. Each spectrum exhibits three distinct peaks at 2.43 eV, 2.62 eV, and 2.84 eV that correspond to the transition to the lowest excited state (S0→ S1) and its vibronic progression known from single molecules in solutions or solid matrices. A comparison with monomer spectra on mica surfaces and solution spectra is shown as well. The monomeric behavior on both substrates can be readily understood by the presence of flat lying PTCDA molecules and the fact that the in-plane excitonic interactions are negligible (nearest neighbor distance≈ 1 nm). However, the comparison reveals three surprising yet characteristic features of the spectra on KCl: (i) the peaks are extremely narrow, (ii) the peak shapes are asymmetric, and (iii) the peak position is coverageindependent. The typical line shape and widths of monomer spectra are a result of different contributions. First, there are homogenously broadened lines for each transition, as clearly visible in C O M M U N IC A IO N
TL;DR: In this paper, high throughput epitaxy of a thin ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF−TrFE) film is demonstrated on a molecularly ordered poly(tetrafluoro methylene) substrate based on spin coating method over the area of a few centimeter square.
Abstract: High throughput epitaxy of a thin ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF−TrFE) film is demonstrated on a molecularly ordered poly(tetrafluoroethylene) (PTFE) substrate based on spin coating method over the area of a few centimeter square. The lattice match between (010)PVDF−TrFE and (100)PTFE results in b and c axes of PVDF−TrFE crystals preferentially parallel to a and c of PTFE, respectively and consequently produces global ordering of the edge-on PVDF−TrFE crystalline lamellae aligned perpendicular to the rubbing direction of PTFE, its c-axis. The epitaxially grown PVDF−TrFE film is successfully incorporated for arrays of ferroelectric capacitors that exhibit not only the significant reduction of ferroelectric thermal hysteresis but also the descent remanent polarization at very low effective operating voltage of ±5 V maintained to 88% of its initial value after number of fatigue cycles of 5 × 108 in the mode of bipolar pulse switching. A ferroelectric field effect transisto...
TL;DR: Cerium oxide was grown epitaxially on a Cu(111) substrate at 520k in an oxygen atmosphere and resulted in a high quality CeO2(1.5) overlayers.
TL;DR: In this article, a cone-shape-patterned sapphire substrate (CSPSS) was used to grow InGaN-GaN thin films, which showed a shorter lattice constant of 5.1877 Aring along the c-axis for the GaN thin film grown on CSPSS, compared to 5.1913 A for the samples grown on a conventional sappire substrate (CSS).
Abstract: High-quality InGaN-GaN film was grown on a cone-shape-patterned sapphire substrate (CSPSS) by using metal-oganic chemical vapor deposition. The growth mode of GaN on CSPSS was similar to that of the epitaxial lateral overgrowth (ELOG), because the growth, in the initial stage, proceeds only on flat basal sapphire substrate and there is no preferential growth plane on the cone region. An analysis of X-ray diffraction showed a shorter lattice constant of 5.1877 Aring along the c-axis for the GaN thin films grown on CSPSS, compared to 5.1913 A for the samples grown on a conventional sapphire substrate (CSS). This is because the ELOG-like mode of the GaN layer over the cone-shaped region results in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate. The output power of a sideview light-emitting diode (LED) grown on CSPSS was estimated to be 7.3 mW at a forward current of 20 mA, which is improved by 34% compared to that of an LED grown on CSS. The significant enhancement in output power is attributed to both the increase of the extraction efficiency, resulted from the increase in photon escaping probability due to enhanced light scattering at the CSPSS, and the improvement of the crystal quality due to the reduction of dislocation.
TL;DR: Single nanowire field effect transistors based on unintentionally doped GaAs nanowires were fabricated and found to display a strong effect of surface states on their transport properties.
Abstract: Epitaxial growth of vertical GaAs nanowires on Si (111) substrates is demonstrated by metal−organic chemical vapor deposition via a vapor−liquid−solid growth mechanism. Systematic experiments indicate that substrate pretreatment, pregrowth alloying temperature, and growth temperature are all crucial to vertical epitaxial growth. Nanowire growth rate and morphology can be well controlled by the growth temperature, the metal−organic precursor molar fraction, and the molar V/III ratio. The as-grown GaAs nanowires have a predominantly zinc-blende crystal structure along a ⟨111⟩ direction. Crystallographic {111} stacking faults found perpendicular to the growth axis could be almost eliminated via growth at high V/III ratio and low temperature. Single nanowire field effect transistors based on unintentionally doped GaAs nanowires were fabricated and found to display a strong effect of surface states on their transport properties.
TL;DR: In this paper, the position of the valence band onset in the x-ray photoemission spectra of the epitaxial films is found to be inconsistent with the widely quoted value of 3.75eV for the fundamental bandgap.
Abstract: Thin films of In2O3 have been grown on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy with a substrate temperature of 650°C. Ordered epitaxial growth was confirmed by high resolution transmission electron microscopy. The position of the valence band onset in the x-ray photoemission spectra of the epitaxial films is found to be inconsistent with the widely quoted value of 3.75eV for the fundamental bandgap of In2O3 and suggests a revised value of 2.67eV.
TL;DR: In this paper, three different growth sequences based on metal-organic vapor phase epitaxy with an emphasis on initial nucleation processes were used to grow a 600-nm-thick AlN.
Abstract: AlN layers were grown directly on sapphire (0001) substrates using three different growth sequences based on metal-organic vapor phase epitaxy with an emphasis on initial nucleation processes. These three methods were simultaneous, alternating supply of aluminum and nitrogen sources, and a combination of the two. In all the methods, nucleation was initiated by three-dimensional (3D) islands with a typical diameter of ∼20nm. Enhanced migration by the alternating source supply caused highly 3D AlN ridge structures at the sapphire molecular steps. These ridge structures prevented a flattened AlN surface and, in addition, moderated lattice relaxation, suggesting the importance of controlling the initial nucleation in determining the film’s properties. In fact, the hybridized method, derived from the simultaneous and alternating supply methods, was able to control the initial nucleation, and provided the best film quality; the 600-nm-thick AlN grown by this method had an atomically flat surface free of pits an...
TL;DR: In this paper, a low-temperature process for covalent bonding of thermal SiO2 to plasma-enhanced chemical vapor deposited (PECVD) SiO 2 for Si-compound semiconductor integration is reported.
Abstract: We report a low-temperature process for covalent bonding of thermal SiO2 to plasma-enhanced chemical vapor deposited (PECVD) SiO2 for Si-compound semiconductor integration. A record-thin interfacial oxide layer of 60 nm demonstrates sufficient capability for gas byproduct diffusion and absorption, leading to a high surface energy of 2.65 J/m2 after a 2-h 300°C anneal. O2 plasma treatment and surface chemistry optimization in dilute hydrofluoric (HF) solution and NH4OH vapor efficiently suppress the small-size interfacial void density down to 2 voids/cm2, dramatically increasing the wafer-bonded device yield. Bonding-induced strain, as determined by x-ray diffraction measurements, is negligible. The demonstration of a 50 mm InP epitaxial layer transferred to a silicon-on-insulator (SOI) substrate shows the promise of the method for wafer-scale applications.