Showing papers on "Epitaxy published in 2011"

Formation of Bilayer Bernal Graphene: Layer-by-Layer Epitaxy via Chemical Vapor Deposition

Abstract: We report the epitaxial formation of bilayer Bernal graphene on copper foil via chemical vapor deposition. The self-limit effect of graphene growth on copper is broken through the introduction of a second growth process. The coverage of bilayer regions with Bernal stacking can be as high as 67% before further optimization. Facilitated with the transfer process to silicon/silicon oxide substrates, dual-gated graphene transistors of the as-grown bilayer Bernal graphene were fabricated, showing typical tunable transfer characteristics under varying gate voltages. The high-yield layer-by-layer epitaxy scheme will not only make this material easily accessible but reveal the fundamental mechanism of graphene growth on copper.

In-Situ Doping of Arsenic for Source and Drain Epitaxy

Abstract: A method includes forming a gate stack over a semiconductor region, and recessing the semiconductor region to form a recess adjacent the gate stack. A silicon-containing semiconductor region is epitaxially grown in the recess to form a source/drain stressor. Arsenic is in-situ doped during the step of epitaxially growing the silicon-containing semiconductor region.

Graphene epitaxy by chemical vapor deposition on SiC.

Abstract: We demonstrate the growth of high quality graphene layers by chemical vapor deposition (CVD) on insulating and conductive SiC substrates. This method provides key advantages over the well-developed...

1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on Si substrates.

Abstract: We report the first operation of an electrically pumped 1.3-μm InAs/GaAs quantum-dot laser epitaxially grown on a Si (100) substrate. The laser structure was grown directly on the Si substrate by molecular beam epitaxy. Lasing at 1.302 μm has been demonstrated with threshold current density of 725 A/cm2 and output power of ~26 mW for broad-area lasers with as-cleaved facets at room temperature. These results are directly attributable to the optimized growth temperature of the initial GaAs nucleation layer.

Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire

Abstract: Green GaInN/GaN quantum well light-emitting diode (LED) wafers were grown on nanopatterned c-plane sapphire substrate by metal-organic vapor phase epitaxy. Without roughening the chip surface, such LEDs show triple the light output over structures on planar sapphire. By quantitative analysis the enhancement was attributed to both, enhanced generation efficiency and extraction. The spectral interference and emission patterns reveal a 58% enhanced light extraction while photoluminescence reveals a doubling of the internal quantum efficiency. The latter was attributed to a 44% lower threading dislocation density as observed in transmission electron microscopy. The partial light output power measured from the sapphire side of the unencapsulated nanopatterned substrate LED die reaches 5.2 mW at 525 nm at 100 mA compared to 1.8 mW in the reference LED.

Epitaxially grown semiconducting hexagonal boron nitride as a deep ultraviolet photonic material

Abstract: Hexagonal boron nitride (hBN) has emerged as an important material for various device applications and as a template for graphene electronics. Low-dimensional hBN is expected to possess rich physical properties, similar to graphene. The synthesis of wafer-scale semiconducting hBN epitaxial layers with high crystalline quality and electrical conductivity control has not been achieved but is highly desirable. Large area hBN epitaxial layers (up to 2 in. in diameter) were synthesized by metal organic chemical vapor deposition. P-type conductivity control was attained by in situ Mg doping. Compared to Mg-doped wurtzite AlN, which possesses a comparable energy band gap (∼6 eV), dramatic reductions in Mg acceptor energy level and P-type resistivity (by about six to seven orders of magnitude) have been realized in hBN epilayers. The ability of conductivity control and wafer-scale production of hBN opens up tremendous opportunities for emerging applications, ranging from revolutionizing p-layer approach in III-ni...

Method of manufacturing semiconductor device

Abstract: PROBLEM TO BE SOLVED: To provide a method for manufacturing a high-performance bipolar transistor in which emitter size dependence of the transistor characteristics is reduced SOLUTION: A silicon oxide film 102 provided with an opening on an N epitaxial layer 101, a polysilicon 103 containing boron and in contact with the N epitaxial layer around the opening, a silicon nitride film 104, a silicon oxide film 105 and a silicon nitride film 106 are formed Next, a base region 108 is formed by depositing and heat-treating a BSG film 107, the BSG film 107 is exposed by depositing and etching back a silicon nitride film 109 with anisotropic etching, and a P-base region is exposed by etching back with anisotropic etching Next, a silicon oxide film with a thickness about 60% with respect to that of the BSG film 107 is formed, an undercut under a lower portion of the silicon nitride film is etched back by embedded isotropic etching, the film thickness of arsenic-doped polysilicon is uniformized by decreasing the undercut, and impurity concentration and depth of an emitter region are uniformized

III–V Nanowires on Si Substrate: Selective-Area Growth and Device Applications

Abstract: III-V nanowires (NWs) on Si are promising building blocks for future nanoscale electrical and optical devices on Si platforms. We present position-controlled and orientation-controlled growth of InAs, GaAs, and InGaAs NWs on Si by selective-area growth, and discuss how to control growth directions of III-V NW on Si. Basic studies on III-V/Si interface showing heteroepitaxial growth with misfit dislocations and coherent growth without misfit dislocations are presented. Finally, we demonstrate the integrations of a III-V NW-based vertical surrounding-gate field-effect transistor and light-emitting diodes array on Si. These demonstrations could have broad applications in high-electron-mobility transistors, laser diodes, and photodiodes with a functionality not enabled by conventional NW devices.

Molecular-beam epitaxy and robust superconductivity of stoichiometric FeSe crystalline films on bilayer graphene

Abstract: We report on molecular beam epitaxy growth of stoichiometric and superconducting FeSe crystalline thin films on double-layer graphene. Layer-by-layer growth of high-quality films has been achieved in a well-controlled manner by using Se-rich condition, which allow us to investigate the thickness-dependent superconductivity of FeSe. In situ low-temperature scanning tunneling spectra reveal that the local superconducting gap in the quasiparticle density of states is visible down to two triple layers for the minimum measurement temperature of 2.2 K, and that the transition temperature ${T}_{\mathrm{c}}$ scales inversely with film thickness.

Method and apparatus for fabricating crack-free Group III nitride semiconductor materials

Abstract: A method and apparatus for growing low defect, optically transparent, colorless, crack-free, substantially flat, single crystal Group III nitride epitaxial layers with a thickness of at least 10 microns is provided. These layers can be grown on large area substrates comprised of Si, SiC, sapphire, GaN, AlN, GaAs, AlGaN and others. In one aspect, the crack-free Group III nitride layers are grown using a modified HVPE technique. If desired, the shape and the stress of Group III nitride layers can be controlled, thus allowing concave, convex and flat layers to be controllably grown. After the growth of the Group III nitride layer is complete, the substrate can be removed and the freestanding Group III nitride layer used as a seed for the growth of a boule of Group III nitride material. The boule can be sliced into individual wafers for use in the fabrication of a variety of semiconductor structures (e.g., HEMTs, LEDs, etc.).

InxGa1-xAs Nanowires on Silicon: One-Dimensional Heterogeneous Epitaxy, Bandgap Engineering, and Photovoltaics

Abstract: We report on the one-dimensional (1D) heteroepitaxial growth of In(x)Ga(1-x)As (x = 0.2-1) nanowires (NWs) on silicon (Si) substrates over almost the entire composition range using metalorganic chemical vapor deposition (MOCVD) without catalysts or masks. The epitaxial growth takes place spontaneously producing uniform, nontapered, high aspect ratio NW arrays with a density exceeding 1 × 10(8)/cm(2). NW diameter (∼30-250 nm) is inversely proportional to the lattice mismatch between In(x)Ga(1-x)As and Si (∼4-11%), and can be further tuned by MOCVD growth condition. Remarkably, no dislocations have been found in all composition In(x)Ga(1-x)As NWs, even though massive stacking faults and twin planes are present. Indium rich NWs show more zinc-blende and Ga-rich NWs exhibit dominantly wurtzite polytype, as confirmed by scanning transmission electron microscopy (STEM) and photoluminescence spectra. Solar cells fabricated using an n-type In(0.3)Ga(0.7)As NW array on a p-type Si(111) substrate with a ∼ 2.2% area coverage, operates at an open circuit voltage, V(oc), and a short circuit current density, J(sc), of 0.37 V and 12.9 mA/cm(2), respectively. This work represents the first systematic report on direct 1D heteroepitaxy of ternary In(x)Ga(1-x)As NWs on silicon substrate in a wide composition/bandgap range that can be used for wafer-scale monolithic heterogeneous integration for high performance photovoltaics.

Three-Dimensional Multiple-Order Twinning of Self-Catalyzed GaAs Nanowires on Si Substrates

Abstract: In this paper we introduce a new paradigm for nanowire growth that explains the unwanted appearance of parasitic nonvertical nanowires. With a crystal structure polarization analysis of the initial stages of GaAs nanowire growth on Si substrates, we demonstrate that secondary seeds form due to a three-dimensional twinning phenomenon. We derive the geometrical rules that underlie the multiple growth directions observed experimentally. These rules help optimizing nanowire array devices such as solar or water splitting cells or of more complex hierarchical branched nanowire devices.

Epitaxial growth of Bi2Se3 topological insulator thin films on Si (111)

Abstract: In this paper, we report the epitaxial growth of Bi2Se3 thin films on Si (111) substrate, using molecular beam epitaxy (MBE). We show that the as-grown samples have good crystalline quality, and their surfaces exhibit terracelike quintuple layers. Angel-resolved photoemission experiments demonstrate single-Dirac-conelike surface states. These results combined with the temperature- and thickness-dependent magneto-transport measurements, suggest the presence of a shallow impurity band. Below a critical temperature of ∼100K, the surface states of a 7 nm thick film contribute up to 50% of the total conduction.

Methods for fabricating a finfet integrated circuit on a bulk silicon substrate

Abstract: Methods are provided for fabricating a FINFET integrated circuit that includes epitaxially growing a first silicon germanium layer and a second silicon layer overlying a silicon substrate. The second silicon layer is etched to form a silicon fin using the first silicon germanium layer as an etch stop. The first silicon germanium layer underlying the fin is removed to form a void underlying the fin and the void is filled with an insulating material. A gate structure is then formed overlying the fin.

Axial InP nanowire tandem junction grown on a silicon substrate.

Abstract: Tandem InP nanowire pn-junctions have been grown on a Si substrate using metal-organic vapor phase epitaxy. In situ HCl etching allowed the different subcomponents to be stacked on top of each other in the axial extension of the nanowires without detrimental radial growth. Electro-optical measurements on a single nanowire tandem pn-junction device show an open-circuit voltage of 1.15 V under illumination close to 1 sun, which is an increase of 67% compared to a single pn-junction device.

Direct Observation of a Noncatalytic Growth Regime for GaAs Nanowires

Abstract: We identify a new noncatalytic growth regime for molecular beam epitaxially grown GaAs nanowires (NWs) that may provide a route toward axial heterostructures with discrete material boundaries and atomically sharp doping profiles. Upon increase of the As/Ga flux ratio, the growth mode of self-induced GaAs NWs on SiO(2)-masked Si(111) is found to exhibit a surprising discontinuous transition in morphology and aspect ratio. For effective As/Ga ratios 1 an immediate onset of NW growth is observed indicating a transition to droplet-free, facet-driven selective area growth with low vertical growth rates. Distinctly different microstructures, facet formation and either the presence or absence of Ga droplets at the apex of NWs, are further elucidated by transmission electron microscopy. The results show that the growth mode transition is caused by an abrupt change from As- to Ga-limited conditions at the (111)-oriented NW growth front, allowing precise tuning of the dominant growth mode.

Optical Absorption Properties of BaSi2 Epitaxial Films Grown on a Transparent Silicon-on-Insulator Substrate Using Molecular Beam Epitaxy

Abstract: We have grown 100-nm-thick BaSi2 films on transparent silicon-on-insulator (SOI) substrates using molecular beam epitaxy, for optical absorption measurements. The SOI substrate has a 0.7-µm-thick (111)-oriented Si layer on top of a fused silica substrate. Reflection high-energy electron diffraction and θ–2θ X-ray diffraction patterns showed that a-axis-oriented BaSi2 layers were grown epitaxially. The absorption spectrum of the film measured in a transmission configuration at room temperature revealed that BaSi2 has a large absorption coefficient of 3 ×104 cm-1 at 1.5 eV and an indirect optical absorption edge of 1.34 eV.

Electronic structure and transport anisotropy of Bi 2 Te 3 and Sb 2 Te 3

Abstract: On the basis of detailed ab initio studies, the influence of strain on the anisotropy of the transport distribution of the thermoelectrics Bi${}_{2}$Te${}_{3}$ and Sb${}_{2}$Te${}_{3}$ was investigated. Both tellurides were studied in their own as well as in their copartner's lattice structure to gain insight into the electrical transport in epitaxial heterostructures composed of both materials. It is shown that the anisotropy of the transport distribution overestimates the experimental findings for Bi${}_{2}$Te${}_{3}$, implying anisotropic scattering effects. An increase of the in-plane lattice constant leads to an enhancement of the transport anisotropy for $p$ doping, whereas the opposite occurs for $n$ doping. The recent findings and special features of the transport distribution are discussed in detail in relation to the topology of the band structures.

Epitaxial growth of InGaN nanowire arrays for light emitting diodes.

Abstract: Significant synthetic challenges remain for the epitaxial growth of high-quality InGaN across the entire compositional range. One strategy to address these challenges has been to use the nanowire geometry because of its strain relieving properties. Here, we demonstrate the heteroepitaxial growth of InxGa1–xN nanowire arrays (0.06 ≤ x ≤ 0.43) on c-plane sapphire (Al2O3(001)) using a halide chemical vapor deposition (HCVD) technique. Scanning electron microscopy and X-ray diffraction characterization confirmed the long-range order and epitaxy of vertically oriented nanowires. Structural characterization by transmission electron microscopy showed that single crystalline nanowires were grown in the ⟨002⟩ direction. Optical properties of InGaN nanowire arrays were investigated by absorption and photoluminescence measurements. These measurements show the tunable direct band gap properties of InGaN nanowires into the yellow-orange region of the visible spectrum. To demonstrate the utility of our HCVD method for ...

Growth and Characterization of AlN and AlGaN Epitaxial Films on AlN Single Crystal Substrates

Abstract: AlN and AlGaN epitaxial films were deposited by metal organic chemical vapor deposition on single crystal AlN substrates processed from AlN boules grown by physical vapor transport. Structural, chemical, and optical characterization demonstrated the high crystalline quality of the films and interfaces.

Selective-area catalyst-free MBE growth of GaN nanowires using a patterned oxide layer.

Abstract: GaN nanowires (NWs) were grown selectively in holes of a patterned silicon oxide mask, by rf-plasma-assisted molecular beam epitaxy (PAMBE), without any metal catalyst. The oxide was deposited on a thin AlN buffer layer previously grown on a Si(111) substrate. Regular arrays of holes in the oxide layer were obtained using standard e-beam lithography. The selectivity of growth has been studied varying the substrate temperature, gallium beam equivalent pressure and patterning layout. Adjusting the growth parameters, GaN NWs can be selectively grown in the holes of the patterned oxide with complete suppression of the parasitic growth in between the holes. The occupation probability of a hole with a single or multiple NWs depends strongly on its diameter. The selectively grown GaN NWs have one common crystallographic orientation with respect to the Si(111) substrate via the AlN buffer layer, as proven by x-ray diffraction (XRD) measurements. Based on the experimental data, we present a schematic model of the GaN NW formation in which a GaN pedestal is initially grown in the hole.

Structural and optical properties of InGaN/GaN nanowire heterostructures grown by PA-MBE

Abstract: The structural and optical properties of InGaN/GaN nanowire heterostructures grown by plasma-assisted molecular beam epitaxy have been studied using a combination of transmission electron microscopy, electron tomography and photoluminescence spectroscopy. It is found that, depending on In content, the strain relaxation of InGaN may be elastic or plastic. Elastic relaxation results in a pronounced radial In content gradient. Plastic relaxation is associated with the formation of misfit dislocations at the InGaN/GaN interface or with cracks in the InGaN nanowire section. In all cases, a GaN shell was formed around the InGaN core, which is assigned to differences in In and Ga diffusion mean free paths.

Growth temperature dependent graphene alignment on Ir(111)

Abstract: The morphology of graphene monolayers on Ir(111) prepared by thermal decomposition of ethylene between 1000 and 1530 K was studied with high resolution low energy electron diffraction. In addition to a well-oriented epitaxial phase, randomly oriented domains are observed for growth temperatures between 1255 and 1460 K. For rotational angles of ±3° around 30° these domains lock-in in a 30° oriented epitaxial phase. Below 1200 K the graphene layer exhibits high disorder and structural disintegrity. Above 1500 K the clear moire spots reflect graphene in a single orientation epitaxial incommensurate phase.

Crystal structure transfer in core/shell nanowires.

Abstract: Structure engineering is an emerging tool to control opto-electronic properties of semiconductors. Recently, control of crystal structure and the formation of a twinning superlattice have been shown for III-V nanowires. This level of control has not been obtained for Si nanowires, the most relevant material for the semiconductor industry. Here, we present an approach, in which a designed twinning superlattice with the zinc blende crystal structure or the wurtzite crystal structure is transferred from a gallium phosphide core wire to an epitaxially grown silicon shell. These materials have a difference in lattice constants of only 0.4%, which allows for structure transfer without introducing extra defects. The twinning superlattices, periodicity, and shell thickness can be tuned with great precision. Arrays of free-standing Si nanotubes are obtained by a selective wet-chemical etch of the core wire.

Thin films and methods of making them using cyclohexasilane

Abstract: Cyclohexasilane is used in chemical vapor deposition methods to deposit epitaxial silicon-containing films over substrates. Such methods are useful in semiconductor manufacturing to provide a variety of advantages, including uniform deposition over heterogeneous surfaces, high deposition rates, and higher manufacturing productivity. Furthermore, the crystalline Si may be in situ doped to contain relatively high levels of substitutional carbon by carrying out the deposition at a relatively high flow rate using cyclohexasilane as a silicon source and a carbon-containing gas such as dodecalmethylcyclohexasilane or tetramethyldisilane under modified CVD conditions.

Terahertz spectroscopy studies on epitaxial vanadium dioxide thin films across the metal-insulator transition

Abstract: We present results on terahertz (THz) spectroscopy on epitaxial vanadium dioxide (VO2) films grown on sapphire across the metal-insulator transition. X-ray diffraction indicates the VO2 film is highly oriented with the crystallographic relationship: (002)film//(0006)sub and [010]film//[21¯1¯0]sub. THz studies measuring the change in transmission as a function of temperature demonstrate an 85% reduction in transmission as the thin film completes its phase transition to the conducting phase, which is much greater than the previous observation on polycrystalline films. This indicates the crucial role of microstructure and phase homogeneity in influencing THz properties.