Showing papers on "Epitaxy published in 2007"

High-efficiency GaInP∕GaAs∕InGaAs triple-junction solar cells grown inverted with a metamorphic bottom junction

Abstract: The authors demonstrate a thin, Ge-free III–V semiconductor triple-junction solar cell device structure that achieved 33.8%, 30.6%, and 38.9% efficiencies under the standard 1sun global spectrum, space spectrum, and concentrated direct spectrum at 81suns, respectively. The device consists of 1.8eV Ga0.5In0.5P, 1.4eV GaAs, and 1.0eV In0.3Ga0.7As p-n junctions grown monolithically in an inverted configuration on GaAs substrates by organometallic vapor phase epitaxy. The lattice-mismatched In0.3Ga0.7As junction was grown last on a graded GaxIn1−xP buffer. The substrate was removed after the structure was mounted to a structural “handle.” The current-matched, series-connected junctions produced a total open-circuit voltage over 2.95V at 1sun.

Twin-free uniform epitaxial GaAs nanowires grown by a two-temperature process

Abstract: We demonstrate vertically aligned epitaxial GaAs nanowires of excellent crystallographic quality and optimal shape, grown by Au nanoparticle-catalyzed metalorganic chemical vapor deposition. This is achieved by a two-temperature growth procedure, consisting of a brief initial high-temperature growth step followed by prolonged growth at a lower temperature. The initial high-temperature step is essential for obtaining straight, vertically aligned epitaxial nanowires on the (111)B GaAs substrate. The lower temperature employed for subsequent growth imparts superior nanowire morphology and crystallographic quality by minimizing radial growth and eliminating twinning defects. Photoluminescence measurements confirm the excellent optical quality of these two-temperature grown nanowires. Two mechanisms are proposed to explain the success of this two-temperature growth process, one involving Au nanoparticle-GaAs interface conditions and the other involving melting-solidification temperature hysteresis of the Au-Ga nanoparticle alloy.

Effect of Molecular Weight on the Structure and Morphology of Oriented Thin Films of Regioregular Poly(3-hexylthiophene) Grown by Directional Epitaxial Solidification†

Abstract: Regioregular head-to-tail (HT)-coupled poly(3-hexylthiophene-2,5-diyl) (P3HT) with a weight-average molecular weight (Mw) in the 7.3–69.6 kDa range is crystallized by directional epitaxial solidification in 1,3,5-trichlorobenzene (TCB) to yield highly oriented thin films. An oriented and periodic lamellar structure consisting of crystalline lamellae separated by amorphous interlamellar zones is evidenced by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both the overall crystallinity as well as the orientation of the crystalline lamellae decrease significantly with increasing Mw. The total lamellar periodicity is close to the length of “fully extended” chains for Mw = 7.3 kDa (polystyrene-equivalent molecular weight, eq. PS) and it saturates to a value of ca. (25–28) ± 2 nm for Mw ≥ 18.8 kDa (eq. PS). This behavior is attributed to a transition from an oligomeric-like system, for which P3HT chains are essentially in a fully extended all-trans conformation and do not fold, to a semicrystalline system that involves a periodic alternation of crystalline lamellae separated by extended amorphous interlamellar zones, which harbor chain folds, chain ends, and tie molecules. For P3HT with Mw of ca. 7.3 kDa (eq. PS), epitaxial crystallization on TCB allows for the growth of both “edge-on” and “flat-on” oriented crystalline lamellae on the TCB substrate. The orientation of the lamellae is attributed to 1D epitaxy. Because of the large size of the “flat-on” crystalline lamellae, a characteristic single-crystal electron diffraction pattern corresponding to the [001] zone was obtained by selected area electron diffraction (SAED), indicating that P3HT crystallizes in a monoclinic unit cell with a = 16.0 A, b = 7.8 A, c = 7.8 A, and γ = 93.5°.

Semiconductor device and method of manufacturing the same

Abstract: A semiconductor device having a vertical gate and method of manufacturing the same are disclosed An example semiconductor device includes a pair of first source/drain regions formed apart from each other by a predetermined distance on a silicon substrate, a first silicon epitaxial layer formed on the pair of first source/drain regions, a vertical gate insulation layer formed at both sidewalls of the first silicon epitaxial layer, and a second silicon epitaxial layers formed on the first silicon epitaxial layer and on the gate insulation layer The example device includes a pair of second source/drain regions formed in the second silicon epitaxial layer formed on the first silicon epitaxial layer, at positions above the pair of first source/drain regions, and a plurality of vertical gates respectively connected to the second silicon epitaxial layer formed on the gate insulation layer and to the pair of second source/drain regions

Room temperature ferromagnetism in Zn1−xCuxO thin films

Abstract: Here the authors report systematic studies on the epitaxial growth and properties of Zn1−xCuxO (x=0.02–0.1) thin films deposited onto sapphire c-plane single crystals using pulsed-laser deposition. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) were employed to study the epitaxial relations of Zn1−xCuxO with the substrate, and x-ray photoelectron spectroscopy was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature ferromagnetism was observed in the Zn1−xCuxO films with magnetic moment per Cu atom decreasing with an increasing Cu content. The presence of any magnetic phase was ruled out using HRTEM. Thus, the ferromagnetism was attributed to Cu ions substituted into the ZnO lattice.

Nanoholes fabricated by self-assembled gallium nanodrill on GaAs(100)

Abstract: Self-assembled nanodrill technology based on droplet epitaxy growth was developed to obtain nanoholes on a GaAs(100) surface. In this technology, the gallium droplets act like “electrochemical drills” etching away the GaAs substrate beneath to give rise to nanoholes more than 10nm deep. The driving force of the nanodrill is attributed to the arsenic desorption underneath the gallium droplet at high growth temperatures and Ga-rich condition. This nanodrill technology provides an easy and flexible method to fabricate nanohole templates on GaAs(100) surface and has great potential for developing quantum dots and quantum dot molecules for quantum computation applications.

Heteroepitaxy of Semiconductors: Theory, Growth, and Characterization

Abstract: Introduction Properties of Semiconductors Introduction Crystallographic Properties Lattice Constants and Thermal Expansion Coefficients Elastic Properties Surface Free Energy Dislocations Planar Defects Problems References Heteroepitaxial Growth Introduction Vapor Phase Epitaxy (VPE) Molecular Beam Epitaxy (MBE) Silicon, Germanium, and Si1-xGex Alloys Silicon Carbide III-Arsenides, III-Phosphides, and III-Antimonides III-Nitrides II-VI Semiconductors Conclusion Problems References Surface and Chemical Considerations in Heteroepitaxy Introduction Surface Reconstructions Nucleation Growth Modes Nucleation Layers Surfactants in Heteroepitaxy Quantum Dots and Self-Assembly Problems References Mismatched Heteroepitaxial Growth and Strain Relaxation Introduction Pseudomorphic Growth and the Critical Layer Thickness Dislocation Sources Interactions between Misfit Dislocations Lattice Relaxation Mechanisms Quantitative Models for Lattice Relaxation Lattice Relaxation on Vicinal Substrates: Crystallographic Tilting of Heteroepitaxial Layers Lattice Relaxation in Graded Layers Lattice Relaxation in Superlattices and Multilayer Structures Dislocation Coalescence, Annihilation, and Removal in Relaxed Heteroepitaxial Layers Thermal Strain Cracking in Thick Films Problems References Characterization of Heteroepitaxial Layers Introduction X-Ray Diffraction Electron Diffraction Microscopy Crystallographic Etching Techniques Photoluminescence Growth Rate and Layer Thickness Composition and Strain Determination of Critical Layer Thickness Crystal Orientation Defect Types and Densities Multilayered Structures and Superlattices Growth Mode Problems References Defect Engineering in Heteroepitaxial Layers Introduction Buffer Layer Approaches Reduced Area Growth Using Patterned Substrates Patterning and Annealing Epitaxial Lateral Overgrowth (ELO) Pendeo-Epitaxy Nanoheteroepitaxy Planar Compliant Substrates Free-Standing Semiconductor Films Conclusion Problems References Appendix A: Bandgap Engineering Diagrams Appendix B: Lattice Constants and Coefficients of Thermal Expansion Appendix C: Elastic Constants Appendix D: Critical Layer Thickness Appendix E: Crystallographic Etches Appendix F: Tables for X-Ray Diffraction Index

Gallium phosphide nanowires as a substrate for cultured neurons.

Abstract: Dissociated sensory neurons were cultured on epitaxial gallium phosphide (GaP) nanowires grown vertically from a gallium phosphide surface Substrates covered by 25 μm long, 50 nm wide nanowires supported cell adhesion and axonal outgrowth Cell survival was better on nanowire substrates than on planar control substrates The cells interacted closely with the nanostructures, and cells penetrated by hundreds of wires were observed as well as wire bending due to forces exerted by the cells

Selective Formation of Silicon Carbon Epitaxial Layer

Abstract: Methods for formation of epitaxial layers containing n-doped silicon are disclosed, including methods for the formation and treatment of epitaxial layers in semiconductor devices, for example, Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices. Formation of the n-doped epitaxial layer involves exposing a substrate in a process chamber to deposition gases including a silicon source, a carbon source and an n-dopant source at a first temperature and pressure and then exposing the substrate to an etchant at a second higher temperature and a higher pressure than during deposition.

Weak Epitaxy Growth Affording High‐Mobility Thin Films of Disk‐Like Organic Semiconductors

Abstract: Thin films of phthalocyanine compounds show weak epitaxial growth on a monodomain film of a rod-like molecule (see figure). The resulting organic electronic devices exhibit high charge carrier mobilities close to those of the single-crystal devices.

Defect reduction of GaAs epitaxy on Si (001) using selective aspect ratio trapping

Abstract: Metal-organic chemical vapor deposition growth of GaAs on Si was studied using the selective aspect ratio trapping method. Vertical propagation of threading dislocations generated at the GaAs∕Si interface was suppressed within an initial thin GaAs layer inside SiO2 trenches with aspect ratio >1, leading to defect-free GaAs regions up to 300nm in width. Cross-sectional and plan-view transmission electron microscopies were used to characterize the defect reduction. Material quality was confirmed by room temperature photoluminescence measurements. This approach shows great promise for the fabrication of optoelectronic integrated circuits on Si substrates.

The role of oxygen vacancies in epitaxial-deposited ZnO thin films

Abstract: ZnO thin films were epitaxial deposited on sapphire (0001) substrates at various temperatures by using the pulsed laser deposition (PLD) technique. An x-ray diffractometer (XRD) was used to investigate the structural properties of the thin film. It was found that all of the thin films were (0002) oriented and the intensity of (0002) peak increased with the increasing growth temperature. The ϕ-scans for the thin films indicated that the thin film grown at a temperature higher than 400 °C had an epitaxial relation with the substrate. An atomic force microscope (AFM) was used to investigate the surface morphologies of the thin films. The surface roughness and grain size of the thin films increased with increasing growth temperature. A double-beam spectrophotometer was used to measure the transmittances of the thin films. The band gap energies of the thin films were calculated by linear fitting the absorption edges for high-quality thin films. A spectrometer was used to investigate the photoluminescent (PL) p...

UV assisted low temperature epitaxial growth of silicon-containing films

Abstract: A method of preparing a clean substrate surface for blanket or selective epitaxial deposition of silicon-containing and/or germanium-containing films. In addition, a method of growing the silicon-containing and/or germanium-containing films, where both the substrate cleaning method and the film growth method are carried out at a temperature below 750° C., and typically at a temperature from about 700° C. to about 500° C. The cleaning method and the film growth method employ the use of radiation having a wavelength ranging from about 310 nm to about 120 nm in the processing volume in which the silicon-containing film is grown. Use of this radiation in combination with particular partial pressure ranges for the reactive cleaning or film-forming component species enable the substrate cleaning and epitaxial film growth at temperatures below those previously known in the industry.

Epitaxy of GaN on silicon—impact of symmetry and surface reconstruction

Abstract: GaN-on-silicon is a low-cost alternative to growth on sapphire or SiC. Today epitaxial growth is usually performed on Si(111), which has a threefold symmetry. The growth of single crystalline GaN on Si(001), the material of the complementary metal oxide semiconductor (CMOS) industry, is more difficult due to the fourfold symmetry of this Si surface leading to two differently aligned domains. We show that breaking the symmetry to achieve single crystalline growth can be performed, e.g. by off-oriented substrates to achieve single crystalline device quality GaN layers. Furthermore, an exotic Si orientation for GaN growth is Si(110), which we show is even better suited as compared to Si(111) for the growth of high quality GaN-on-silicon with a nearly threefold reduction in the full width at half maximum (FWHM) of the -scan. It is found that a twofold surface symmetry is in principal suitable for the growth of single crystalline GaN on Si.

A growth diagram for plasma-assisted molecular beam epitaxy of In-face InN

Abstract: We investigated the role of temperature and In∕N flux ratios to determine suitable growth windows for the plasma-assisted molecular beam epitaxy of In-face (0001) InN. Under vacuum, InN starts decomposing at 435°C as defined by the release of N2 from the InN crystal and a buildup of an In adlayer and liquid In droplets on the sample surface. At temperatures greater than 470°C, InN decomposition was characterized by a release of both In vapor and N2 in the absence of a significant accumulation of an In adlayer. No growth was observed at substrate temperatures above 500°C or at temperatures in which the decomposition rates were higher than the growth rates. A growth diagram was then constructed consisting of two growth regimes: the “In-droplet regime” characterized by step-flow growth and relatively flat surfaces and the “N-rich regime” characterized by rough, three-dimensional surfaces. The growth diagram can then be used to predict the surface structure of films grown at varying substrate temperatures and...

Metal-organic vapor phase epitaxy and properties of AlInN in the whole compositional range

Abstract: The authors present a detailed study of Al1−xInxN layers covering the whole composition range of 0.09

Direct observation of the structural component of the metal-insulator phase transition and growth habits of epitaxially grown VO2 nanowires.

Abstract: We have grown epitaxially orientation-controlled monoclinic VO2 nanowires without employing catalysts by a vapor-phase transport process. Electron microscopy results reveal that single crystalline VO2 nanowires having a [100] growth direction grow laterally on the basal c plane and out of the basal r and a planes of sapphire, exhibiting triangular and rectangular cross sections, respectively. In addition, we have directly observed the structural phase transition of single crystalline VO2 nanowires between the monoclinic and tetragonal phases which exhibit insulating and metallic properties, respectively, and clearly analyzed their corresponding relationships using in situ transmission electron microscopy.

High Thermal Conductivity of Gallium Nitride (GaN) Crystals Grown by HVPE Process

Abstract: A relatively large sample of gallium nitride (GaN) was grown as a single crystal using the hydride vapor phase epitaxy (HVPE) process. The thermal diffusivity of the single crystal has been measured using a vertical-type laser flash method. The thermal expansion was measured using a dilatometer in order to estimate the thermal diffusivity with sufficient reliability. The effect of sample thickness and temperature on thermal diffusivity was evaluated. The specific heat capacity of GaN was also measured by using a differential scanning calorimeter. The thermal properties of single-crystal GaN have been compared with the measured thermal properties of single-crystal silicon carbide (SiC). The thermal conductivity of single-crystal GaN at room temperature is found to be 253 � 8:8% W/mK, which is approximately 60% of the value obtained for SiC. The excellent thermal property that is obtained in this study clearly indicates that GaN crystals are one of the promising materials for use in high-power-switching devices. [doi:10.2320/matertrans.MRP2007109]

Devices including graphene layers epitaxially grown on single crystal substrates

Abstract: An electronic device comprises a body including a single crystal region on a major surface of the body. The single crystal region has a hexagonal crystal lattice that is substantially lattice-matched to graphene, and a at least one epitaxial layer of graphene is disposed on the single crystal region. In a currently preferred embodiment, the single crystal region comprises multilayered hexagonal BN. A method of making such an electronic device comprises the steps of: (a) providing a body including a single crystal region on a major surface of the body. The single crystal region has a hexagonal crystal lattice that is substantially lattice-matched to graphene, and (b) epitaxially forming a at least one graphene layer on that region. In a currently preferred embodiment, step (a) further includes the steps of (al) providing a single crystal substrate of graphite and (a2) epitaxially forming multilayered single crystal hexagonal BN on the substrate. The hexagonal BN layer has a surface region substantially lattice-matched to graphene, and step (b) includes epitaxially forming at least one graphene layer on the surface region of the hexagonal BN layer. Applications to FETs are described.

Effect of substrate-induced strains on the spontaneous polarization of epitaxial BiFeO3 thin films

Abstract: A single-domain thermodynamic theory is employed to predict the spontaneous polarizations of (001)c, (101)c, and (111)c oriented epitaxial BiFeO3 thin films grown on dissimilar substrates. The effects of various substrate-induced strains on the spontaneous polarization were studied. The dependences of the spontaneous polarization on film orientations and the types of substrate-induced strains were analyzed.

Epitaxial Growth of Indium Arsenide Nanowires on Silicon Using Nucleation Templates Formed by Self‐Assembled Organic Coatings

Abstract: Indium arsenide nanowires are grown directly on silicon substrates (see figure and cover) using a method employing self-assembled organic coatings to create oxide-based growth templates. High-performance materials, such as InAs, could have great impact on future nanoelectronics if integrated with Si, but integration has so far been hard to realize with other methods.

High mobility vanadyl-phthalocyanine polycrystalline films for organic field-effect transistors

Abstract: The organic films of vanadyl-phthalocyanine (VOPc) compounds showed weak epitaxy growth (WEG) behavior on thin ordered para-sexiphenyl (p-6P) layer with high substrate temperature. The WEG of VOPc molecules standing up on the p-6P layer leaded to high in-plane orientation and their layer-by-layer growth behavior. In consequence, high quality VOPc films were obtained, which were consisted of lamellar crystals. Organic field-effect transistors with VOPc∕p-6P films as active layers realized high mobility of above 1cm2∕Vs. This result indicated that nonplanar compounds can obtain a device performance better than planar compounds, therefore, it may provide a rule to find disklike organic semiconductor materials.

Morphology- and orientation-controlled gallium arsenide nanowires on silicon substrates.

Abstract: GaAs nanowires were epitaxially grown on Si(001) and Si(111) substrates by using Au-catalyzed vapor−liquid−solid (VLS) growth in a solid source molecular beam epitaxy system Scanning electron microscopy analysis revealed that almost all the GaAs nanowires were grown along 〈111〉 directions on both Si substrates for growth conditions investigated The GaAs nanowires had a very uniform diameter along the growth direction X-ray diffraction data and transmission electron microscopy analysis revealed that the GaAs〈111〉 nanowires had a mixed crystal structure of the hexagonal wurtzite and the cubic zinc-blende Current−voltage characteristics of junctions formed by the epitaxially grown GaAs nanowires and the Si substrate were investigated by using a current-sensing atomic force microscopy

On the lattice parameters of GaN

Abstract: The lattice parameters of low-defect density, undoped bulk GaN fabricated by hydride vapor phase epitaxy (HVPE) on (0001) sapphire and subsequent substrate removal, are precisely determined using high-resolution x-ray diffraction. The obtained values, c=5.18523A and a=3.18926A, are compared with the lattice parameters of freestanding HVPE GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high-pressure technique and homoepitaxial GaN is made, and significant differences in the lattice parameters are found. The observed differences are discussed and a possible explanation is suggested.

Use of ZnO thin films as sacrificial templates for metal organic vapor phase epitaxy and chemical lift-off of GaN

Abstract: Continued development of GaN-based light emitting diodes is being hampered by constraints imposed by current non-native substrates. ZnO is a promising alternative substrate but it decomposes under the conditions used in conventional GaN metal organic vapor phase epitaxy (MOVPE). In this work, GaN was grown on ZnO/c-Al2O3 using low temperature/pressure MOVPE with N2 as a carrier and dimethylhydrazine as a N source. Characterization confirmed the epitaxial growth of GaN. The GaN was lifted-off the c-Al2O3 by chemically etching away the ZnO underlayer. This approach opens up the way for bonding of the GaN onto a support of choice.

Adsorption-controlled molecular-beam epitaxial growth of BiFeO3

Abstract: BiFeO3 thin films have been deposited on (111) SrTiO3 single crystal substrates by reactive molecular-beam epitaxy in an adsorption-controlled growth regime. This is achieved by supplying a bismuth overpressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO3 to control stoichiometry. Four-circle x-ray diffraction reveals phase-pure, untwinned, epitaxial, (0001)-oriented films with rocking curve full width at half maximum values as narrow as 25arcsec (0.007°). Second harmonic generation polar plots combined with diffraction establish the crystallographic point group of these untwinned epitaxial films to be 3m at room temperature.

Epitaxial lateral overgrowth of (112¯2) semipolar GaN on (11¯00) m-plane sapphire by metalorganic chemical vapor deposition

Abstract: The authors report the growth of semipolar (112¯2) GaN films on nominally on-axis (101¯0) m-plane sapphire substrates using metal organic chemical vapor deposition. High-resolution x-ray diffraction (XRD) results indicate a preferred (112¯2) GaN orientation. Moreover, epitaxial lateral overgrowth (ELO) of GaN was carried out on the (112¯2) oriented GaN templates. When the ELO stripes were aligned along [112¯0]sapphire, the Ga-polar wings were inclined by 32° with respect to the substrate plane with smooth extended nonpolar a-plane GaN surfaces and polar c-plane GaN growth fronts. When compared with the template, the on-axis and off-axis XRD rocking curves indicated significant improvement in the crystalline quality by ELO for this mask orientation (on-axis 1700arcsec for the template, 380arcsec for the ELO sample, when rocked toward the GaN m axis), as verified by transmission electron microscopy (TEM). For growth mask stripes aligned along [0001]sapphire with GaN m-plane as growth fronts, the surface was...

Fabrication of the hybrid ZnO LED structure grown on p-type GaN by metal organic chemical vapor deposition

Abstract: LEDs based on the n-ZnO/p-GaN heterojunction were successfully fabricated with the top/middle/bottom layer sequence of ZnO/ZnO nanorods/p-GaN by continuously controlling the growth parameters via metal organic chemical vapor deposition. The ZnO top layer was deposited as a contact layer for the application of nanorods as an active layer, while p-GaN was used as a p-type layer, instead of p-ZnO. The ZnO film grown on ZnO nanorods with high crystalline quality on GaN exhibited the epitaxial properties of a single domain. The light-emitting device fabricated using this hybrid structure demonstrated a forward turn-on voltage of 11 V and a high reverse current, which require further development for device fabrication.

Solid phase epitaxy versus random nucleation and growth in sub-20nm wide fin field-effect transistors

Abstract: The authors investigate the implications of amorphizing ion implants on the crystalline integrity of sub-20nm wide fin field-effect transistors (FinFETs). Recrystallization of thin body silicon is not as straightforward as that of bulk silicon because the regrowth direction may be parallel to the silicon surface rather than terminating at it. In sub-20nm wide FinFETs surface proximity suppresses crystal regrowth and promotes the formation of twin boundary defects in the implanted regions. In the case of a 50nm amorphization depth, random nucleation and growth leads to polycrystalline silicon formation in the top ∼25nm of the fin, despite being only ∼25nm from the crystalline silicon seed.