Metalorganic Chemical Vapor Deposition Technique Research Articles

Bilayer structures based on metal phthalocyanine and palladium layers for selective hydrogen detection

In this work, bilayer structures in which a Pd layer was deposited on the surface of palladium phthalocyanine film (PdPc/Pd) by a Metal-Organic Chemical Vapor Deposition technique were studied as active layers of chemiresistive sensors for selective detection of hydrogen. Surface morphology, microstructure and composition of Pd layers were investigated by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Three sets of bilayer structures with Pd layer thicknesses of 55–80 nm, 100–120 nm and 140–160 nm were obtained to examine the effect of the thickness on the electrical sensor response toward gaseous hydrogen (1–30 v.%). It has been shown that the bilayer structures with 55–80 nm thick Pd layers exhibit the maximal sensor response and can be effectively used for selective detection of hydrogen in the concentration range from 1 to 30% in the presence of gaseous ammonia, CO2, NO2, and chlorinated alkane vapours.

Growth and characterization of high quality N-type GaSb/GaAs heterostructure by IMF growth mode using MOCVD for low power application

In this study, we demonstrate the growth of a 150-nm-thick GaSb layer on a GaAs substrate with excellent film quality using the interfacial misfit dislocation growth mode by the Metal–Organic Chemical Vapor Deposition technique. The n-type GaSb epilayer grown on the GaAs substrate has a low threading dislocation density of 3.2 × 106 cm−2 and a surface roughness of approximately 0.8 nm. A high carrier mobility up to 4600 cm2 V−1 s−1 with a carrier concentration of 1.2 × 1017 cm−3 is achieved in this study. The fabricated Al2O3/GaSb/GaAs MOSCAP demonstrated excellent capacitance–voltage (C–V) characteristics with a small frequency dispersion of approximately 2.8%/decade. The results demonstrate the potential of high-mobility Sb-based materials on GaAs for p-type channel CMOS applications in the future.

Magnetoresistance Relaxation Anisotropy of Nanostructured La-Sr(Ca)-Mn-O Films Induced by High-Pulsed Magnetic Fields

The results of investigation of colossal magnetoresistance relaxation in nanostructured La-Sr(Ca)-Mn-O films upon removal of magnetic field pulse are presented. Thin films having thicknesses of 75-350 nm grown by pulsed injection metal-organic chemical vapor deposition technique were studied in pulsed magnetic fields having duration of 0.9 ms and amplitudes of 2-12 T. It was obtained that “fast” relaxation process occurring in hundred microseconds time scale exhibits anisotropy: the magnitude of remnant resistivity is approximately three times smaller and the process is faster when magnetic field is applied perpendicular to the film plane in comparison with in-plane direction. The dynamics of this relaxation process was analyzed using Kolmogorov-Avrami-Fatuzzo model, taking into account nucleation and reorientation of magnetic domains into equilibrium state. The “fast” remnant relaxation was not observed after the application of longer pulses (20 ms) having amplitude of 60 T. Influence of remnant relaxation on operation of B-scalar magnetic field sensors based on nanostructured manganite films is discussed.

Synthesis, crystal structure and vapour pressure studies of novel nickel complex as precursor for NiO coating by metalorganic chemical vapour deposition technique

A square planar nickel complex namely bis(N-propyl-3-methylsalicylaldimine)nickel(II) (2) was prepared from its parent compound bis(3-methylsalicylaldehydato)nickel(II) (1) by adding n-propylamine in a methanol medium. The TG/DTA analysis of the resultant Schiff's base complex 2 in the solid phase was evaluated in an inert N2 environment at atmospheric pressure. Complex 2 was completely volatile giving nil residue at 335 °C in a single weight loss step, whereas the complex 1 was found to be non-volatile giving 47% residues till 455 °C. The change in volatility of 2 was brought about by the condensation of n-propylamine with 1 which replaced aldehyde O (-CH=O) with N (-CH=N). The volatile precursor 2 was characterised by single crystal XRD, 1H and 13C NMR, FT-IR, C, H and N elemental analysis and mass spectrometry. The temperature dependence of the saturated vapour pressure and enthalpy of vapourisation (ΔvapH° = 97.9 ± 2.0 kJ mol−1) of the volatile complex 2 was determined by a transpiration TG technique in the temperature range 499–562 K. Subsequently, it was used as a precursor for the deposition of nickel oxide (NiO) thin film on Si(100) substrate by employing plasma assisted metal-organic chemical vapour deposition (PAMOCVD) technique. The nano-crystalline nickel oxide thin films were analysed by XRD and SEM/EDX. X-ray photoelectron spectroscopy (XPS) study confirmed the formation of stoichiometric NiO phase. The band gap of the NiO thin film was found to be 4.31eV exhibiting a blue shift as observed from DRS-UV.

Effects of Mg-doping on characteristics of semi-polar [formula omitted] plane p-AlGaN films

The effects of Mg-doping on the characteristics of semi-polar (112¯2) plane Al0.15Ga0.85N films grown on (101¯0) m-plane sapphire substrates with metal-organic chemical vapor deposition (MOCVD) technique were investigated intensively and systematically. The characterization results showed that the crystalline quality of the (112¯2) plane AlGaN films could be improved by optimizing the Mg-delta-doping process. Whereas, the surface morphology for the samples was monotonously degraded with increasing the Mg-doping level. Meanwhile, a hole concentration as high as 5.4×1017cm−3 were achieved by optimizing the Mg-doping level. Furthermore, the luminescence mechanism of the samples was investigated by photoluminescence spectra at room temperature.

Evaluation of elliptical optical cavity for a combustion thermophotovoltaic system

A reflective cavity with elliptical cross-section is proposed to couple a burner to three arrays of thermophotovoltaic (TPV) cells. Burner and photoconverter, with triangular section, are located near the two foci of the ellipse. The elliptical cavity is designed to be inserted into a thermo-electric micro-cogenerator for residential use, which exploits the TPV cells to convert visible and infrared radiation generated by the burner into electricity. Taking into account the key construction constraints, several cavity configurations, which differ for components or optical properties, are analysed by ray tracing simulations. The maximum radiation collection efficiency is 62% for the elliptical cavity and is reduced to 48% by introducing quartz protections around the burner and the receiver. A germanium-based photoconverter is developed and manufactured by metalorganic chemical vapour deposition techniques. Each photoconverter can deliver 180mW/cm2 (at 230mV voltage and 55°C) when illuminated by a blackbody spectrum at 1473K. The manufacture of the TPV receiver is described and the thermal design aspects are considered. The use of a dichroic filter for a TPV generator configuration based on an elliptical chamber is also evaluated.

Metal Ir coatings on endocardial electrode tips, obtained by MOCVD

The present work demonstrates the application of the Metal-Organic Chemical Vapor Deposition technique to fabricate metal iridium coatings onto the pole tips of endocardial electrodes. Using iridium (III) acetylacetonate as a volatile precursor, the target coatings were successfully applied to the working surface of cathodes and anodes of pacemaker electrodes in the flow type reactor in hydrogen atmosphere at deposition temperature of 550°C. The coating samples were characterized by means of XRD, SEM, Raman- and XPS-spectroscopies. The formation of non-textured coatings with fractal-like morphology and 7–24nm crystallite size has been realized. The electrochemical properties of the coatings were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The charge storage capacity values of the electrochemically activated samples were 17.0–115mCcm−2 and 14.4–76.5mCcm−2 for measurements carried out in 0.1M sulfuric acid and in phosphate buffer saline solutions, respectively. A comparison of some characteristics of the samples obtained with commercially available cathode of pacemaker electrodes is also presented.

Research on ZnO/Si heterojunction solar cells**Project supported by the State Key Development Program for Basic Research of China (Nos. 2011CBA00706, 2011CBA00707), the Tianjin Applied Basic Research Project and Cutting-Edge Technology Research Plan (No. 13JCZDJC26900), the Tianjin Major Science and Technology Support Project (No. 11TXSYGX22100), the National High Technology Research and Development Program of China (No. 2013AA050302), and the Fundamental Research

We put forward an n-ZnO/p-Si heterojunction solar cell model based on AFORS-HET simulations and provide experimental support in this article. ZnO:B (B-doped ZnO) thin films deposited by metal-organic chemical vapor deposition (MOCVD) are planned to act as electrical emitter layer on p-type c-Si substrate for photovoltaic applications. We investigate the effects of thickness, buffer layer, ZnO:B affinity and work function of electrodes on performances of solar cells through computer simulations using AFORS-HET software package. The energy conversion efficiency of the ZnO:B(n)/ZnO/c-Si(p) solar cell can achieve 17.16% (: 675.8 mV, : 30.24 mA/cm2, FF: 83.96%) via simulation. On a basis of optimized conditions in simulation, we carry out some experiments, which testify that the ZnO buffer layer of 20 nm contributes to improving performances of solar cells. The influences of growth temperature, thickness and diborane (B2H6) flow rates are also discussed. We achieve an appropriate condition for the fabrication of the solar cells using the MOCVD technique. The obtained conversion efficiency reaches 2.82% (: 294.4 mV, : 26.108 mA/cm2, FF: 36.66%).

Structure, morphology and Raman and optical spectroscopic analysis of In1−xCuxP thin films grown by MOCVD technique for solar cell applications

Nanocrystalline In1−xCuxP thin films (0≤x≤0.5) have been deposited on quartz substrates by a Metal-Organic Chemical Vapor Deposition (MOCVD) technique. The effect of the copper ion content on the structural crystal lattice, morphology and optical behavior of the InP thin films was assessed using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectroscopy and spectrophotometry. All films exhibited a crystalline cubic zinc blende structure, inferring the solubility of the Cu atoms in the InP crystal structure. The XRD patterns demonstrated that the inclusion of Cu atoms into the InP films forced the nanoparticles in the films to grow along the (111) direction. The AFM topography showed that the Cu ions reduce the surface roughness of deposited films. The Raman spectra of the deposited films contain the first and second order anti-stoke ΓTO, ΓLO, ΧLO+ΧTO, 2ΓTO, and ΓLO+ΓTO bands which are characteristic of the InP crystalline structure. The intensities of these bands decreased with increasing the content of the Cu atoms in the InP crystals implying the creation of a stacking fault density in the InP crystal structure. The In1−xCuxP thin films have shown high optical transparency of 90%. An increase of the optical band gap from 1.38eV to 1.6eV was assigned to the increase of the amount of Cu ions in the InP films. The In0.5Cu0.5P thin film exhibited remarkable optical conductivity with very low dissipation factor which makes it a promising buffer window for solar energy applications.

Magnesium incorporation efficiencies in MgxZn1−xO films on ZnO substrates grown by metalorganic chemical vapor deposition**Project supported by the National Natural Science Foundation of China (Grant No. 61474121) and the Major Scientific Project of Fujian Province, China (Grant No. 2014NZ0002-2).

We investigate the magnesium (Mg) incorporation efficiencies in MgxZn1−xO films on c-plane Zn-face ZnO substrates by using metalorganic chemical vapor deposition (MOCVD) technique. In order to deposit high quality MgxZn1−xO films, atomically smooth epi-ready surfaces of the hydrothermal grown ZnO substrates are achieved by thermal annealing in O2 atmosphere and characterized by atomic force microscope (AFM). The AFM, scanning electron microscope (SEM), and x-ray diffraction (XRD) studies demonstrate that the MgxZn1−xO films each have flat surface and hexagonal wurtzite structure without phase segregation at up to Mg content of 34.4%. The effects of the growth parameters including substrate temperature, reactor pressure and VI/II ratio on Mg content in the films are investigated by XRD analysis based on Vegard’s law, and confirmed by photo-luminescence spectra and x-ray photoelectron spectroscopy as well. It is indicated that high substrate temperature, low reactor pressure, and high VI/II ratio are good for obtaining high Mg content.

Growth of hierarchical GaN nanowires for optoelectronic device applications

Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers, and nanofluidic biochemical sensors. We report on the growth of hierarchical GaN nanowires (NWs) by dynamically adjusting the growth parameters using the pulsed flow metal-organic chemical vapor deposition technique. We carried out two step growth processes to grow hierarchical GaN NWs. In the first step, the GaN NWs were grown at 950°C, and in the second, we suitably decreased the growth temperature to 630°C and 710°C to grow the hierarchical structures. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and cathodoluminescence measurements. These kinds of hierarchical GaN NWs are promising for allowing flat band quantum structures that are shown to improve the efficiency of LEDs.

Grain size reduction on nanostructured TiO2 thin films due to annealing

TiO2 thin films have been deposited at 300 °C on quartz substrates by a metal–organic chemical vapor deposition technique.

Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

Metamorphic Ga0.76In0.24As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In0.24Al0.76As/p-In0.24Ga0.76As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 1018 cm–3 and completely remove the potential barrier, thereby reducing the series resistance of the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.

Properties of InAsSb films grown on GaSb by metal-organic chemical vapor deposition

We report high quality InAsSb films grown on GaSb substrates using metal-organic chemical vapor deposition (MOCVD) technique through interface engineering. This work shows that the interface quality of the hetero-epitaxial InAsSb layer strongly depends on the V/III ratio during the growth and it plays a crucial role in the surface morphology, composition, and electrical and optical properties of InAsSb films. Furthermore, by properly engineering the interface conditions, high optical quality InAsSb films which show obvious mid-infrared emissions even at room temperature have been obtained. Therefore, this work provides a simple and feasible method for the growth of high quality InAsSb film which can be used for room temperature mid-infrared optoelectronics.

Van der Waals epitaxy of CdTe thin film on graphene

van der Waals epitaxy (vdWE) facilitates the epitaxial growth of materials having a large lattice mismatch with the substrate. Although vdWE of two-dimensional (2D) materials on 2D materials have been extensively studied, the vdWE for three-dimensional (3D) materials on 2D substrates remains a challenge. It is perceived that a 2D substrate passes little information to dictate the 3D growth. In this article, we demonstrated the vdWE growth of the CdTe(111) thin film on a graphene buffered SiO2/Si substrate using metalorganic chemical vapor deposition technique, despite a 46% large lattice mismatch between CdTe and graphene and a symmetry change from cubic to hexagonal. Our CdTe films produce a very narrow X-ray rocking curve, and the X-ray pole figure analysis showed 12 CdTe (111) peaks at a chi angle of 70°. This was attributed to two sets of parallel epitaxy of CdTe on graphene with a 30° relative orientation giving rise to a 12-fold symmetry in the pole figure. First-principles calculations reveal that, despite the relatively small energy differences, the graphene buffer layer does pass epitaxial information to CdTe as the parallel epitaxy, obtained in the experiment, is energetically favored. The work paves a way for the growth of high quality CdTe film on a large area as well as on the amorphous substrates.

An analysis of the growth of silver catalyzed InxGa1−xAs nanowires on Si (100) by metal organic chemical vapor deposition

A model is proposed here to understand the nucleation of III–V semiconductor nanowires (NW). Whereas the classical nucleation theory is not adequately sufficient in explaining the evolution of the shape of the NWs under different chemical environment such as flow rate or partial pressure of the precursors, the effect of adsorption and desorption mediated growth, and diffusion limited growth are taken into account to explain the morphology and the crystal structure of InxGa1−xAs nanowires (NW) on Silicon (100) substrates grown by a metalorganic chemical vapor deposition technique. It is found that the monolayer nucleus that originates at the triple phase line covers the entire nucleus-substrate (NS) region at a specific level of supersaturation and there are cases when the monolayer covers a certain fraction of the NS interface. When the monolayer covers the total NS interface, NWs grow with perfect cylindrical morphology and whenever a fraction of the interface is covered by the nucleus, the NWs become curved as observed from high resolution transmission electron microscopy images. The supersaturation, i.e., the chemical potential is found to be governed by the concentration of precursors into the molten silver which in the present case is taken as a catalyst. Our study provides new insights into the growth of ternary NWs which will be helpful in understanding the behavior of growth of different semiconducting NWs.

Electron traps as major recombination centers in n-GaN films grown by metalorganic chemical vapor deposition

For a group of n-GaN films grown by metalorganic chemical vapor deposition (MOCVD) using both straight MOCVD and epitaxial lateral overgrowth techniques (ELOG proper or pendeo overgrowth), the spectra of deep traps were measured by deep-level transient spectroscopy (DLTS) with electrical or optical injection (ODLTS). The results were compared with diffusion length measurement results obtained from electron-beam-induced current experiments. The results strongly indicate that deep electron traps near Ec − 0.56 eV could be the major recombination centers determining the diffusion length values in pendeo samples.

Atomic-Scale Spectroscopy of Gated Monolayer MoS2.

The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS2 by atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal-organic chemical vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topographic measurements of defect density indicate a sample quality comparable to single-crystal MoS2. From gate voltage dependent spectroscopic measurements, we determine that in-gap states exist in or near the MoS2 film at a density of 1.3 × 10(12) eV(-1) cm(-2). By combining the single-particle band gap measured by STS with optical measurements, we estimate an exciton binding energy of 230 meV on this substrate, in qualitative agreement with numerical simulation. Grain boundaries are observed in these polycrystalline samples, which are seen to not have strong electronic signatures in STM imaging.

Study of Charge Carrier Transport in GaN Sensors.

Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm2/Vs for electrons, and μh = 400 ± 80 cm2/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects.

Development of technological building blocks for the monolithic integration of ammonia-MBE-grown GaN-HEMTs with silicon CMOS

In this paper, we investigate a technological route for the monolithic integration of GaN high-electron-mobility transistors (HEMTs) on silicon complementary metal oxide semiconductor (CMOS) circuits. The CMOS-first approach developed in this work relies on the ammonia-source molecular beam epitaxy (ammonia-MBE) technique which operates at noticeably lower temperatures than the metalorganic chemical vapor deposition (MOCVD) technique. The presence of CMOS devices on the wafer is a challenge that has been addressed by reducing the maximum growth temperature of (Al,Ga)N materials from 920 to 830–850 °C without any degradation of the GaN crystal quality nor the HEMT device behavior. In addition, we developed a dielectric stack able to withstand the large stress arising from the growth process and to mitigate the related cracking and delamination issues. Capacitance–voltage measurements have shown that the HEMT epitaxial structures provide a capacitance plateau with a sharp pinch-off behavior, attesting the absence of any significant interface traps nor residual donor contamination due to the presence of a dielectric mask on the silicon substrate. Preliminary results show that thin buffer HEMT devices with normal electrical behaviors can be locally grown at low temperature.