Metallorganic Chemical Vapor Deposition Research Articles

Large-Signal Linearity and High-Frequency Noise of Passivated AlGaN/GaN High-Electron Mobility Transistors.

This study proposes AlGaN/GaN/silicon high-electron mobility transistors (HEMTs) grown by a metallorganic chemical vapor deposition (MOCVD) system. The large-signal linearity and high-frequency noise of HEMTs without and with different passivation layers are compared. The experimental data show that the addition of a TiO2 passivation layer to undoped AlGaN/GaN HEMT’s increases the value of the third-order intercept point (OIP3) by up to 70% at 2.4 GHz. Furthermore, the minimum noise figure (NFmin) of the HEMT with TiO2 passivation is significantly reduced.

Visible-light photocatalytic activity and recyclability of N-doped TiO2 films grown by MOCVD

Abstract Nitrogen-doped TiO2 films were grown on borosilicate glass substrates at 400 °C by the metallorganic chemical vapor deposition (MOCVD) for removing dye from water under visible light. The effect of N-doping on the structural, surface, and photocatalytic properties of films was evaluated. X-ray photoelectron spectroscopy (XPS) analyses revealed that 1.56 and 2.44 at% of nitrogen were incorporated into the films by varying the NH3 flux during the growth. Methyl orange dye degradation experiments showed that the N-doped films presented photoactivity under visible light. The film containing 2.44 at% of nitrogen exhibited the best photocatalytic behavior, with 55% of efficiency. Recyclability tests under visible light showed that the film efficiency dropped gradually after each test. N-TiO2 films grown by MOCVD have the potential to be used in environmental applications by removing pollutants using a green method under sunlight or even under internal illumination, although its reuse is limited.

Effect of nitrogen-doping on the surface chemistry and corrosion stability of TiO2 films

TiO2 and N-doped TiO2 films were grown on AISI 316 stainless steel substrates and on Si (100) by metallorganic chemical vapor deposition (MOCVD) at 400°C and 500°C. X-ray photoelectron spectroscopy, scanning electron microscopy, and contact angle techniques were used to characterize de films. The corrosion behavior was assessed by monitoring the open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization tests in 3.5wt% NaCl solution at room temperature. The results show that 6.18 at% of nitrogen was introduced in the films grown at 400°C and 8.23 at% at 500°C, and that besides TiO2, nitrogen phases were identified. All the films are hydrophilic and the contact angles varied from 48° to 72°. The films presented good homogeneity, low porosity and rounded grains in the range of 40–90nm. The RMS roughness varied between 5.5 and 18.5nm. Titanium dioxide films grown at 400°C showed better corrosion resistance than those grown at 500°C due to its compact morphology. Nitrogen-doping was not efficient to protect the substrate from corrosion.

Growth stages of nano-structured mixed-phase titania thin films and effect on photocatalytic activity

The development of nano-structured mixed-phase titania thin films and the relationship to photocatalytic activity (PCA) is of interest for pollution reduction and antimicrobial applications. A set of films grown by pulsed pressure metallorganic chemical vapour deposition using titanium tetraisopropoxide precursor was studied. The growth method is single-stage, scalable and produces high-quality, adherent films. Film thicknesses were 101 nm to 4.0 μm. Three growth stages were identified. All films were a mixture of anatase and rutile. Early stage films had rounded morphologies, low surface roughness and low PCA. Transition stage films developed columnar [110] orientated anatase dendrites, contained amorphous carbon and had reduced UV transmittance. Late stage films had strong anatase (220) and rutile (200) textures, contained amorphous carbon and exhibited highly branched anatase dendrites with nanoscale secondary plates. PCA was determined from degradation of stearic acid and correlated with increasing surface roughness. The most active film had formal quantum efficiency of (6.62 ± 0.64) × 10−4 molecules/photon, 59 times higher than a commercially available control. The performance is attributed to the combination of phases yielding polymorphic phase boundaries and amorphous carbon enhancing the adsorption of organic molecules, the unusual (220) anatase texture yielding nanostructured anatase dendrites in combination with nanocrystalline rutile and hierarchical porosity.

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO2 films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti4+ cations by S6+ ions into TiO2 structure of the doped samples. SO42− groups were observed on the surface. S-TiO2 film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO2 films. The results supported the idea that the sulfur-doped TiO2 films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.

Deposition of Magnetite Nanofilms by Pulsed Injection MOCVD in a Magnetic Field.

This report is on the growth of Fe3O4 nanofilms on Al2O3(0001) and MgO(001) substrates with and without the presence of an external magnetic field using a pulsed injection metallorganic chemical vapour deposition (PI MOCVD) technique. The effects of growing magnetic oxide nanofilms in a 1 T field have been examined using various instrumental methods. It was found that the application of a magnetic field during PI MOCVD does not drastically alter the crystalline texture, surface morphology, and film thickness, but it significantly modifies the Fe3O4 film magnetisation and coercive field. Moreover, it was shown that the application of a 1 T field during the cooling of the sample also improves the magnetic properties. We believe that the large external field orients the magnetic spin structure at high temperatures (during growth or the initial stages of cool down) and that cooling through local magnetic ordering temperatures at Fe3O4 defect sites subsequently favours a ferromagnetic spin alignment. The control of magnetic properties of magnetite nanofilms by the application of magnetic fields during growth opens up new routes towards the fabrication and application of magnetic thin film devices.

Precursor Duration and Thermal Annealing Effects in InGaN/GaN Multiple Quantum Wells Grown on Nitrogen-Polar GaN Templates by a Pulsed Metallorganic Chemical Vapor Deposition

In this study, the effects of precursor duration and thermal annealing on the material and optical properties of InGaN/GaN multiple quantum wells (MQWs) grown on nitrogen (N)-polar GaN templates by a pulsed metallorganic chemical vapor deposition are investigated. With a 2-sec NH3 precursor duration, an apparent indium aggregation leads to a higher density and larger size of InGaN mounds for more exciton accumulation, enhancing the radiative recombination and luminescence efficiency. In addition, the more, larger, and brighter light spots in the cathodoluminescence (CL) images and a stronger CL intensity in the annealed sample show that a smaller size and higher density of InGaN mounds enhance the radiative recombination and luminescence efficiency. Both a 2-sec NH3 precursor duration and 60-sec thermal annealing are beneficial to the growth conditions of InGaN/GaN MQWs grown on N-polar GaN templates. The research results of the pulsed growth mode provide important information to optimize growth conditions of InGaN/GaN MQWs grown on N-polar GaN templates.

Tunable SAW Devices Based on Ni:ZnO/ZnO/GaN Structures with Buried IDTs

Tunable RF devices have promising applications in low-power resettable sensors, adaptive signal processing, and secure wireless communications. We report a tunable surface acoustic wave (SAW) device built on a multifunctional ZnO/GaN-based structure. The device consists of a piezoelectric Ni:ZnO (NZO) layer deposited on the top of a ZnO/GaN semiconductor heterostructure. The multifunctional ZnO layers are made through a hybrid deposition technique: RF sputtering of a piezoelectric NZO layer and metallorganic chemical vapor deposition (MOCVD) of a semiconducting n-type ZnO layer on the GaN/Al2O3 substrate. This multifunctional and multilayer structure combines the large electromechanical coupling coefficient of ZnO and high acoustic velocities of GaN. The unique dispersion relationship in ZnO/GaN enables high-frequency (GHz) operation using higher order SAW modes. Two device configurations are designed: one with the interdigital transducer (IDT) exposed on the NZO surface, and one with the IDT buried inside NZO layer. Both devices operate at the GHz frequency. SAW frequency tuning is achieved by voltage controlled acoustoelectric interaction. The device using the buried IDT structure has better performance over the counterpart with exposed IDT SAW. The ZnO/GaN-based tunable SAW device with buried IDTs operating at 1.35 GHz has frequency tunability of ∼0.9% at low biasing voltage range (−12 V∼0 V).

Monolithically integrated InGaAs/GaAs/AlGaAs quantum well laser grown by MOCVD on exact Ge/Si(001) substrate

We report on realization of the InGaAs/GaAs/AlGaAs quantum well laser grown by metallorganic chemical vapor deposition on a virtual Ge-on-Si(001) substrate. The Ge buffer layer has been grown on a nominal Si(001) substrate by solid-source molecular beam epitaxy. Such Ge buffer possessed rather good crystalline quality and smooth surface and so provided the subsequent growth of the high-quality A3B5 laser structure. The laser operation has been demonstrated under electrical pumping at 77 K in the continuous wave mode and at room temperature in the pulsed mode. The emission wavelengths of 941 nm and 992 nm have been obtained at 77 K and 300 K, respectively. The corresponding threshold current densities were estimated as 463 A/cm2 at 77 K and 5.5 kA/cm2 at 300 K.

Deep Traps in AlGaN/GaN High Electron Mobility Transistors on SiC

Capacitance-voltage (C-V) and current-voltage (I-V) characteristics and deep trap spectra were measured for high-power HEMT structures grown by metallorganic chemical vapor deposition on semi-insulating 4H-SiC substrates and comprised of an AlGaN barrier and GaN(Fe) semi-insulating buffer with the upper (∼100 nm) portion unintentionally doped and lightly n-type. The C-V measurements were performed in the 85–400 K range in the dark and showed a decrease in the threshold voltage for temperatures higher than 200 K. The change was most prominent for temperatures from 290 K to ∼330 K and occured due to deep traps capturing electrons in the AlGaN barrier and near the AlGaN/GaN interface. C-V measurements at low temperature showed that the traps in the AlGaN barrier are located near Ec−2 eV and have a density of ∼1012 cm−2, while the traps at the interface have an optical ionization threshold near 1.7 eV and the density of ∼4 × 1012 cm−2. Capacitance deep level transient spectroscopy (DLTS) and current DLTS (CDLTS) revealed electron traps with levels near Ec−0.56 eV and hole traps with levels near Ev+0.9 eV and Ev+0.5 eV. The Ec−0.56 eV traps are known to be located near the AlGaN/GaN interface in the GaN buffer. The Ev+0.9 eV hole traps are located in the buffer.

Characteristics of Naturally Textured Zn1-xMgxO Transparent Conductive Thin Film Fabricated by Sol-Gel Process

Naturally textured Zn1-xMgxO:Al transparent conductive thin film was developed by sol-gel process. Wrinkle-like surface morphology with different surface roughness was achieved by the nonequilibrium solute precipitation and crystallization process occurred during the drying procedure. Using solvent with large evaporation rate or increasing solute concentration enabled the formation of rough wrinkle surface morphology. It can scatter light (λ ≤ 750 nm) stronger than the boron doped ZnO thin film with pyramidal surface morphology, which was deposited by the metallorganic chemical vapor deposition method. An AZMO thin film with slim wrinkle morphology (optical bandgap = 3.6 eV, root-mean-square roughness= 42.3 nm, and sheet resistance= 20.8 Ω/sq) was obtained.

Deposition of pure gold thin films from organometallic precursors

Using metallorganic chemical vapor deposition, pure gold thin films have been obtained from a number of volatile dimethylgold(III) complexes with different types of chelating organic ligands. Deposition was performed in argon (10Torr) with and without hydrogen and oxygen as reactant gases and with additional VUV (vacuum ultraviolet) stimulation. According to the XRD phase analysis, gold films grow mainly in [111] direction. The influence of precursor structure on the morphology of the deposited layers was demonstrated. It was established that presence of H2 raises the growth rate and porosity of the films significantly with decreased amount of any impurities. With the VUV stimulation, the gold content in the films amounts to >99at%.

Analysis of High Aspect Ratio through Silicon via (TSV) Diffusion and Stress Impact Profile during 3D Advanced Integration

This article is related to the development of a protocol for the characterization of the behavior of high aspect ratio through silicon via (TSV) during advanced three dimension (3D) integration. The time-of-flight (TOF)-SIMS profile measurement along the sidewall of the TSV with advanced samples preparations is described. This technique allows studying the efficiency of a low temperature, 200°C metallorganic chemical vapor deposition (MOCVD) titanium nitride (TiN) film as a barrier to copper diffusion into silicon. Then the thermo-mechanical stresses induced by the TSV in the surrounding silicon were studied by micro-Raman spectroscopy. Different TiN films were studied according to subsequent plasma treatments and compared with a reference deposited by ionized physical vapor deposition (i-PVD). The thermal stress in the silicon was found to decrease as a function of distance from an isolated TSV. The iPVD and MOCVD TiN barrier involved a more compressive stress than non-plasma treated MOCVD TiN.

Flexible Thin-Film Tandem Solar Cells With >30% Efficiency

Alta Devices, Inc. has previously reported on single-junction thin-film GaAs photovoltaic devices on flexible substrates with efficiencies up to 28.8% under AM1.5G solar illumination at 1-sun intensity. Here, we show that the same technology platform can be extended to tandem devices that are capable of even higher efficiencies: so far up to 30.8%. Specifically, here, we report on a lattice-matched, series-connected, two-junction device with InGaP as the light-absorbing material of the top cell and GaAs as the absorber in the bottom cell. The material is grown by metallorganic chemical vapor deposition, and then, the device is lifted off by the epitaxial liftoff (ELO) process, as previously reported. This demonstrates that ELO is not only capable of record-setting single-junction performance but capable of achieving world-class efficiency with a multijunction architecture as well.

Cyclic Chemical Vapor Deposition of Nickel Ferrite Thin Films Using Organometallic Precursor Combination

This work introduces the fabrication of nano scale magnetostrictive NiFe2O4 (NFO) thin films using reduced pressure metallorganic chemical vapor deposition (MOCVD) with programmable cyclic pulsing of novel precursor combination — n-butylferrocene and nickelocene. Using a custom-designed CVD system, different rate-limiting steps and Ea in the CVD of iron oxide and nickel oxide depositions are discussed. Both cyclic-deposition and co-deposition modes were investigated through NFO depositions on silicon substrates at 17 Torr and 500°C. Growth rates of NFO films obtained by co-deposition and cyclic-deposition were 3 and 1.6 nm/min, respectively. Material characterizations were conducted on NFO films fabricated at optimized process conditions and annealed samples. Rutherford backscattering spectroscopic results showed better stoichiometric control for cyclic-deposited films. As-deposited NFO films showed homogeneous stoichiometric chemical composition without carbon contamination in the bulk film; a saturation magnetization of 25 emu/g was observed from its trevorite crystalline phase upon annealing at 700°C in argon ambience for one hour.

Atomic scale structure and chemistry of Bi2Te3/GaAs interfaces grown by metallorganic van der Waals epitaxy

Here, we report the atomic scale structure and chemistry of epitaxial Bi2Te3 thin films grown via metallorganic chemical vapor deposition on (001) GaAs substrates. Using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), we report an atomically abrupt interface spanned by a second phase. Further, we demonstrate that interpretation of HAADF STEM image intensities does not provide an unambiguous interface structure. Combining atomic resolution imaging and spectroscopy, we determine the identity of the interfacial species is found to be consistent with that of a bilayer of Ga–Te that terminates GaAs dangling bonds.

DC characteristics of lattice-matched InAlN/AlN/GaN high electron mobility transistors

Lattice-matched InAlN/AlN/GaN high electron mobility transistors (HEMTs) grown on sapphire substrate by using low-pressure metallorganic chemical vapor deposition were prepared, and the comprehensive DC characteristics were implemented by Keithley 4200 Semiconductor Characterization System. The experimental results indicated that a maximum drain current over 400 mA/mm and a peak external transconductance of 215 mS/mm can be achieved in the initial HEMTs. However, after the devices endured a 10-h thermal aging in furnace under nitrogen condition at 300 °C, the maximum reduction of saturation drain current and external transconductance at high gate-source voltage and drain-source voltage were 30% and 35%, respectively. Additionally, an increased drain-source leakage current was observed at three-terminal off-state. It was inferred that the degradation was mainly related to electron-trapping defects in the InAlN barrier layer.

Effect of Barrier Growth Temperature on the Material Properties of InGaN/GaN Multiple Quantum Well Structures

InGaN/GaN multiple quantum well (MQW) structures with different GaN barrier growth temperatures have been grown by metallorganic chemical vapor deposition (MOCVD) and investigated. Double peak InGaN emission was observed and correlated to the barrier growth temperature. It was deduced that the extra emission peak originated from InGaN/GaN nanostructures formed around (VGa-ON)2− point defects mainly at the bottom wells of MQW stack, due to local strain relaxation in the vicinity of point defects and the compositional pulling effect on In. Increasing barrier growth temperature decreases O impurity incorporation and thus prevents the formation of an undesired radiation source in the active layer which decrease the quantum efficiency.

Fabrication of tungsten films by metallorganic chemical vapor deposition

Tungsten films growing on copper substrates were fabricated by metallorganic chemical vapor deposition (MOCVD). The chemical purity, crystallographic phase, cross-sectional texture, and resistivity of the deposited films both before and after annealing treatment were investigated by X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and four-point probe method. It is found that the films deposited at 460°C are metastable β-W with (211) orientation and can change into α-W when annealed in high-purity hydrogen atmosphere at high temperature. There are small amounts of C and O in the films, and the W content of the films increases with increasing deposition temperature and also goes up after annealing in high-purity hydrogen atmosphere. The films have columnar microstructures and the texture evolution during their growth on copper substrates can be divided into three stages. The resistivity of the as-deposited films is in the range of 87–104 μΩ·cm, and low resistivity is obtained after annealing in high-purity hydrogen atmosphere.

Optical Properties of ZnO/MgZnO Multiple Quantum Wells Grown by Metallorganic Chemical Vapor Deposition

We report on the optical properties of ZnO/MgZnO multiple quantum wells (MQWs) with well widths of 0.7, 1.5, and 2 nm, which were grown by metallorganic chemical vapor deposition. The temperature-dependent photoluminescence (PL) measurement showed a weak S-shaped PL property for a localized exciton emission peak with increasing the well width. The internal quantum efficiency (IQE) was increased by 75% when the well width was increased from 0.7 to 2 nm. The improved IQE and weak S-shaped PL property of MQWs with increasing the well width was attributed to decreased defect density and improved uniformity of well thickness in ZnO well layer or improved homogeneity of alloy-potentials in MgZnO barrier layers.