Showing papers on "Epitaxy published in 2006"

Bonded intermediate substrate and method of making same

Abstract: An intermediate substrate includes a handle substrate bonded to a thin layer suitable for epitaxial growth of a compound semiconductor layer, such as a III-nitride semiconductor layer. The handle substrate may be a metal or metal alloy substrate, such as a molybdenum or molybdenum alloy substrate, while the thin layer may be a sapphire layer. A method of making the intermediate substrate includes forming a weak interface in the source substrate, bonding the source substrate to the handle substrate, and exfoliating the thin layer from the source substrate such that the thin layer remains bonded to the handle substrate.

A gallium nitride single-photon source operating at 200 K.

Abstract: Fundamentally secure quantum cryptography has still not seen widespread application owing to the difficulty of generating single photons on demand. Semiconductor quantum-dot structures have recently shown great promise as practical single-photon sources, and devices with integrated optical cavities and electrical-carrier injection have already been demonstrated. However, a significant obstacle for the application of commonly used III–V quantum dots to quantum-information-processing schemes is the requirement of liquid-helium cryogenic temperatures. Epitaxially grown gallium nitride quantum dots embedded in aluminium nitride have the potential for operation at much higher temperatures. Here, we report triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling. Gallium nitride quantum dots also open a new wavelength region in the blue and near-ultraviolet portions of the spectrum for single-photon sources.

Method for forming silicon-containing materials during a photoexcitation deposition process

Abstract: Embodiments of the invention generally provide a method for depositing films or layers using a UV source during a photoexcitation process. The films are deposited on a substrate and usually contain a material, such as silicon (e.g., epitaxy, crystalline, microcrystalline, polysilicon, or amorphous), silicon oxide, silicon nitride, silicon oxynitride, or other silicon-containing materials. The photoexcitation process may expose the substrate and/or gases to an energy beam or flux prior to, during, or subsequent a deposition process. Therefore, the photoexcitation process may be used to pre-treat or post-treat the substrate or material, to deposit the silicon-containing material, and to enhance chamber cleaning processes. Attributes of the method that are enhanced by the UV photoexcitation process include removing native oxides prior to deposition, removing volatiles from deposited films, increasing surface energy of the deposited films, increasing the excitation energy of precursors, reducing deposition time, and reducing deposition temperature.

High electron mobility lattice-matched AlInN∕GaN field-effect transistor heterostructures

Abstract: Room temperature electron mobility of 1170cm2∕Vs is obtained in an undoped, lattice-matched, Al0.82In0.18N∕GaN field-effect transistor heterostructure, while keeping a high (2.6±0.3)×1013cm−2 electron gas density intrinsic to the Al0.82In0.18N∕GaN material system. This results in a two-dimensional sheet resistance of 210Ω∕◻. The high mobility of these layers, grown by metal-organic vapor phase epitaxy on sapphire substrate, is obtained thanks to the insertion of an optimized AlN interlayer, reducing the alloy related interface roughness scattering.

ZnO p-n junction light-emitting diodes fabricated on sapphire substrates

Abstract: A ZnO p-n junction light-emitting diode (LED) was fabricated on a-plane Al2O3 substrate by plasma-assisted molecular-beam epitaxy. NO plasma activated by a radio frequency atomic source was used to grow the p-type ZnO layer of the LED. The current-voltage measurements at low temperatures showed a typical diode characteristic with a threshold voltage of about 4.0V under forward bias. With increasing temperature, the rectification characteristic was degraded gradually, and faded away at room temperature. Electroluminescence band of the ZnO p-n junction LED was located at the blue-violet region and was weakened significantly with increase of temperature. This thermal quenching of the electroluminescence was attributed to the degradation of the diode characteristic with temperature.

Au-free epitaxial growth of InAs nanowires.

Abstract: III-V nanowires have been fabricated by metal-organic vapor-phase epitaxy without using Au or other metal particles as a catalyst. Instead, prior to growth, a thin SiOx layer is deposited on the substrates. Wires form on various III-V substrates as well as on Si. They are nontapered in thickness and exhibit a hexagonal cross-section. From high-resolution X-ray diffraction, the epitaxial relation between wires and substrates is demonstrated and their crystal structure is determined.

Germanium nanowire epitaxy: shape and orientation control.

Abstract: Epitaxial growth of nanowires along the 111 directions was obtained on Ge(111), Ge(110), Ge(001), and heteroepitaxial Ge on Si(001) substrates at temperatures of 350 degrees C or less by gold-nanoparticle-catalyzed chemical vapor deposition. On Ge(111), the growth was mostly vertical. In addition to 111 growth, 110 growth was observed on Ge(001) and Ge(110) substrates. Tapering was avoided by the use of the two-temperature growth procedure, reported earlier by Greytak et al.

Phase transition and critical issues in structure-property correlations of vanadium oxide

Abstract: Vanadium oxide (VO2) exhibits a very interesting semiconductor to metal transition as the crystal structure changes from tetragonal or rutile to monoclinic upon cooling close to 68°C The characteristics of this transition are very interesting scientifically and are of immense technological importance due to a variety of sensor- and memory-type applications We have processed high-quality films of VO2 by pulsed laser deposition, which were grown epitaxially on (0001) sapphire substrate via domain matching epitaxy, involving matching of integral multiples of lattice planes between the film of monoclinic structure and the sapphire substrate These films exhibit a sharp transition near 68°C, large amplitude, and very small hysteresis, similar to bulk single crystal of VO2 The sharpness and amplitude of the transition and the hysteresis upon heating and cooling are found to be a strong function of crystal structure and microstructure (grain size, characteristics of grain boundaries, and defect content) Here

Accurate dependence of gallium nitride thermal conductivity on dislocation density

Abstract: The authors experimentally find that the thermal conductivity of gallium nitride depends critically on dislocation density using the 3-omega technique. For GaN with dislocation densities lower than 106cm−2, the thermal conductivity is independent with dislocation density. The thermal conductivity decreases with a logarithmic dependence for material with dislocation densities in the range of 107–1010cm−2. These results are in agreement with theoretical predictions. This study indicates that the hydride vapor phase epitaxy method offers an attractive route for the formation of semi-insulating gallium nitride with optimal thermal conductivity values around 230W∕mK and very low dislocation density near 5×104cm−2.

Epitaxial deposition process and apparatus

Abstract: An epitaxial deposition process including a dry etch process, followed by an epitaxial deposition process is disclosed The dry etch process involves placing a substrate to be cleaned into a processing chamber to remove surface oxides A gas mixture is introduced into a plasma cavity, and the gas mixture is energized to form a plasma of reactive gas in the plasma cavity The reactive gas enters into the processing chamber and reacts with the substrate, forming a thin film The substrate is heated to vaporize the thin film and expose an epitaxy surface The epitaxy surface is substantially free of oxides Epitaxial deposition is then used to form an epitaxial layer on the epitaxy surface

Fabrication of InP∕InAs∕InP core-multishell heterostructure nanowires by selective area metalorganic vapor phase epitaxy

Abstract: We report the growth of InP∕InAs∕InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values.

Transient terahertz conductivity in photoexcited silicon nanocrystal films

Abstract: Time-resolved terahertz spectroscopy is used to probe ultrafast carrier dynamics and terahertz conductivity in photoexcited thin films of silicon nanocrystals, polynanocrystalline silicon, and epitaxial silicon-on-sapphire. We show that a Drude-Smith model provides an excellent fit to the observed transient terahertz conductivity in all of our samples, revealing a transition from a Drude-like response with low carrier backscatter in bulk silicon-on-sapphire to a non-Drude-like, localized behavior with high carrier backscatter in the silicon nanocrystal films. Evidence for long-range conduction between nanocrystals is observed, and we show that the photoconductive lifetime of the silicon nanocrystals is dominated by trapping at $\mathrm{Si}∕\mathrm{Si}{\mathrm{O}}_{2}$ interface states.

Growth of planar non-polar {1 -1 0 0} m-plane gallium nitride with metalorganic chemical vapor deposition (MOCVD)

Abstract: A method of growing planar non-polar m-plane Ill-Nitride material, such as an m-plane gallium nitride (GaN) epitaxial layer, wherein the Ill-Nitride material is grown on a suitable substrate, such as an m-plane silicon carbide (m-SiC) substrate, using metalorganic chemical vapor deposition (MOCVD). The method includes performing a solvent clean and acid dip of the substrate to remove oxide from the surface, annealing the substrate, growing a nucleation layer such as an aluminum nitride (AlN) on the annealed substrate, and growing the non-polar m-plane Ill-Nitride epitaxial layer on the nucleation layer using MOCVD.

Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals

Abstract: m-Plane (10-10) nonpolar InGaN-based light emitting diodes (LEDs) with no threading dislocations or stacking faults have been realized on m-plane GaN single crystals by conventional metal organic vapor phase epitaxy. The crystalline properties of the material, together with the structures of the LED devices, have been observed by scanning transmission electron microscopy. It is shown that dislocation-free nonpolar nitride layers with smooth surfaces can be obtained under growth conditions involving high V/III ratios, which are the optimized growth conditions for c-plane GaN. The peak wavelength of the electroluminescence emission obtained from the finished devices is 435 nm, which is in the blue region. The output power and the calculated external quantum efficiency are 1.79 mW and 3.1%, respectively, at a driving current of 20 mA.

Flat GaN epitaxial layers grown on Si(111) by metalorganic vapor phase epitaxy using step-graded AlGaN intermediate layers

Abstract: In this work, we report on the growth by metalorganic vapor phase epitaxy (MOVPE) of GaN layers on AlN/Si(111) templates with step-graded AlGaN intermediate layers. First, we will discuss the optimization of the AlN/Si(111) templates and then we will discuss the incorporation of step-graded AlGaN intermediate layers. It is found that the growth stress in GaN on high-temperature (HT) AlN/Si(111) templates is compressive, although, due to relaxation, the stress we have measured is much lower than the theoretical value. In order to prevent the stress relaxation, step-graded AlGaN layers are introduced and a crack-free GaN epitaxial layer of thickness >1 µm is demonstrated. Under optimized growth conditions, the total layer stack, exceeding 2 µm in total, is kept under compressive stress, and the radius of the convex wafer bowing is as large as 119 m. The crystalline quality of the GaN layers is examined by high-resolution x-ray diffraction (HR-XRD), and the full-width-at-half maximums (FWHMs) of the x-ray rocking curve (0002) ω-scan and (−1015) ω-scan are 790 arc sec and 730 arc sec, respectively. It is found by cross-sectional transmission electron microscopy (TEM) that the step-graded AlGaN layers terminate or bend the dislocations at the interfaces.

Sequential Lithographic Methods to Reduce Stacking Fault Nucleation Sites

Abstract: An epitaxial silicon carbide layer is fabricated by forming first features in a surface of a silicon carbide substrate having an off-axis orientation toward a crystallographic direction. The first features include at least one sidewall that is orientated nonparallel (i.e., oblique or perpendicular) to the crystallographic direction. A first epitaxial silicon carbide layer is then grown on the surface of the silicon carbide substrate that includes first features therein. Second features are then formed in the first epitaxial layer. The second features include at least one sidewall that is oriented nonparallel to the crystallographic direction. A second epitaxial silicon carbide layer is then grown on the surface of the first epitaxial silicon carbide layer that includes the second features therein.

Rf-plasma-assisted molecular-beam epitaxy of β-Ga2O3

Abstract: Epitaxial growth of β-Ga2O3 thin films by the rf-plasma-assisted molecular-beam epitaxy technique is demonstrated. Growth on (1 0 0) β-Ga2O3 substrates leads to very smooth epilayers, while (2 0 1¯) and (1 0 0) oriented β-Ga2O3 films are obtained on (0 0 1) sapphire and (1 0 0) MgO substrates, respectively. Internal transmittance, refractive index and direct bandgaps are determined.

Field-induced current modulation in epitaxial film of deep-ultraviolet transparent oxide semiconductor Ga2O3

Abstract: Epitaxial films of a deep-ultraviolet transparent oxide semiconductor, Ga2O3, were fabricated on α-Al2O3 (0001) substrates by pulsed laser deposition. Four-axes x-ray diffraction measurements revealed that the tin-doped Ga2O3 films have a crystal structure different from any known polymorphs of Ga2O3. Its crystal lattice was determined to be an orthorhombic. Top gate field-effect transistor structures were fabricated using the Ga2O3 epitaxial films for n-channels. The channel conductance was modulated by an order of magnitude by gate voltage at room temperature with an estimated field-effect mobility of 5×10−2cm2(Vs)−1.

Position-controlled epitaxial III?V nanowires on silicon

Abstract: We show the epitaxial integration of III–V semiconductor nanowires with silicon technology. The wires are grown by the VLS mechanism with laser ablation as well as metal–organic vapour phase epitaxy. The hetero-epitaxial growth of the III– Vn anowires on silicon was confirmed with x-ray diffraction pole figures and cross-sectional transmission electron microscopy. We show preliminary results of two-terminal electrical measurements of III–V nanowires grown on silicon. E-beam lithography was used to predefine the position of the nanowires. (Some figures in this article are in colour only in the electronic version)

p-type ZnO films with solid-source phosphorus doping by molecular-beam epitaxy

Abstract: Phosphorus-doped p-type ZnO films were grown on r-plane sapphire substrates using molecular-beam epitaxy with a solid-source GaP effusion cell. X-ray diffraction spectra and reflection high-energy electron diffraction patterns indicate that high-quality single crystalline (112¯0) ZnO films were obtained. Hall and resistivity measurements show that the phosphorus-doped ZnO films have high hole concentrations and low resistivities at room temperature. Photoluminescence (PL) measurements at 8 K reveal a dominant acceptor-bound exciton emission with an energy of 3.317 eV. The acceptor energy level of the phosphorus dopant is estimated to be 0.18 eV above the valence band from PL spectra, which is also consistent with the temperature dependence of PL measurements.

c-axis oriented epitaxial BaTiO3 films on (001) Si

Abstract: c-axis oriented epitaxial films of the ferroelectric BaTiO3 have been grown on (001) Si by reactive molecular-beam epitaxy The orientation relationship between the film and substrate is (001) BaTiO3‖(001) Si and [100] BaTiO3‖[110] Si The uniqueness of this integration is that the entire epitaxial BaTiO3 film on (001) Si is c-axis oriented, unlike any reported so far in the literature The thermal expansion incompatibility between BaTiO3 and silicon is overcome by introducing a relaxed buffer layer of BaxSr1−xTiO3 between the BaTiO3 film and silicon substrate The rocking curve widths of the BaTiO3 films are as narrow as 04° X-ray diffraction and second harmonic generation experiments reveal the out-of-plane c-axis orientation of the epitaxial BaTiO3 film Piezoresponse atomic force microscopy is used to write ferroelectric domains with a spatial resolution of ∼100nm, corroborating the orientation of the ferroelectric film

Nature of germanium nanowire heteroepitaxy on silicon substrates

Abstract: Systematic studies of the heteroepitaxial growth of germanium nanowires on silicon substrates were performed. These studies included the effect of sample preparation, substrate orientation, preanneal, growth temperature, and germane partial pressure on the growth of epitaxial germanium nanowires. Scanning electron microscopy and transmission electron microscopy were used to analyze the resulting nanowire growth. Germanium nanowires grew predominantly along the ⟨111⟩ crystallographic direction, with a minority of wires growing along the ⟨110⟩ direction, irrespective of the underlying silicon substrate orientation [silicon (111), (110), and (100)]. Decreasing the partial pressure of germane increased the number of ⟨111⟩ nanowires normal to the silicon (111) surface, compared to the other three available ⟨111⟩ directions. The growth rate of nanowires increased with the partial pressure of germane and to a lesser degree with temperature. The nucleation density of nanowire growth and the degree of epitaxy both...

Catalyst-free growth of In(As)P nanowires on silicon

Abstract: The catalyst-free metal organic vapor phase epitaxial growth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowire growth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InP nanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.

High-Temperature Metal-Organic Vapor Phase Epitaxial Growth of AlN on Sapphire by Multi Transition Growth Mode Method Varying V/III Ratio

Abstract: High-quality AlN layers were grown on c-plane sapphire substrates by high-temperature metal-organic vapor phase epitaxy AlN layers of about 9 µm in thickness with an atomically flat surface were obtained without cracks Multiple modulation of the V/III ratio during growth led to a reduction in the number of dislocations during the growth transition period The dislocation density of the AlN layers was found to be less than 3×108 cm-2