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The epitaxial growth technique of InGaAs photodiode structures based on a digital InGaAs/GaAs metamorphic buffer layer by metalorganic chemical vapor deposition has been developed. The spectral dependence of the photocurrent of photodiodes based on the produced structures has a maximum at the 1.24 μm wavelength. The photosensitivity range at 10% of peak is 1.17–1.29 μm at room temperature. The current-voltage characteristics in the temperature range 9–300 K were investigated. It is shown that the dark current consists of generation-recombination and tunneling components. The dark current density at room temperature was 8 × 10–5 A/cm2 with a reverse bias of –5 V. [ABSTRACT FROM AUTHOR]

Investigation of Co-doped ZnO nanostructures (NS) is of importance to improve ZnO photocatalysis. Co-doped ZnO NS were grown by atmospheric pressure chemical vapor deposition from acetylacetonates Zn and Co in various proportions. The effect of cobalt doping on the structure, morphology, photoluminescence and Raman spectra of ZnO NS was studied. Photocatalysis of Co-doped ZnO NS was investigated by the decomposition of methyl orange dye at Hg lamp excitation. Unlike pure ZnO NS which demonstrate intense deep level emission in PL spectrum, obliged to excess of oxygen vacancies, deposited Co-doped ZnO NS exhibit suppressed emission in visible part of optical spectrum. By the help of Raman spectroscopy cobalt-related secondary phase in ZnO was detected. It was demonstrated that Co-doping reduces the photocatalytic activity of ZnO, presumable, due to absence of oxygen vacancies and reduced possibility to charge transfer from semiconductor to dye molecules. [ABSTRACT FROM AUTHOR]

We demonstrate a broadband second-harmonic generator for the green spectral range based on a periodical polarity GaN waveguide structure. We grew the structure with a periodicity of 4 μ m using an MOCVD (metal-organic chemical vapor deposition) reactor. We tested the structure using femtosecond laser pulse pumping and obtained the second harmonic ( λ SH =512 nm) conversion efficiency 0.79 · 10 - 7 % · W - 1 for the pump peak power of 440 kW inside the waveguide. Based on the theoretical modeling of the dispersion curves of the pump and the second harmonic, we found multiple crossings, including an extended crossing. We relate this fact to the experimentally measured broadened second harmonic spectrum. [ABSTRACT FROM AUTHOR]

In this study, the impact of organometallic chemical vapor deposition (MOCVD) deposition temperature on the growth mechanism of SiOC coatings was studied in detail. For this purpose, four different SiOC coatings were prepared at deposition temperatures of 1050, 1100, 1150, and 1200 °C. The surface morphology and surface roughness of the prepared coatings were examined by field-emission scanning electron microscope (FESEM) and atomic force microscope (AFM), respectively. X-ray photoelectron spectroscopy (XPS) was employed to analyze the composition and structural units in the prepared coatings. The phase structure of SiOC coatings was analyzed by grazing incident diffraction of x-rays (GIXRD) and high resolution transmission electron microscope (HRTEM). Results revealed that, the starting temperature of homogeneous reaction in the cavity is 1100 °C, while the degree of heterogeneous reaction in the cavity reaches its maximum value at 1200 °C. With the increase in deposition temperature, more surface protrusions, a greater degree of homogeneous reaction and the evolution of graphite and 3C-SiC crystalline phases are resulted, which lead to the reduction of deposition rate of SiOC coatings. Furthermore, for SiOC coatings, flat surface morphology and less content of Si-O-Si bonds improve the HF acid etching resistance of SiOC coatings. [ABSTRACT FROM AUTHOR]

Nanostructured zirconium carbide coatings were deposited on the surface of multi-walled carbon nanotubes (MWCNT) by the metal-organic chemical vapor deposition growth technique using bis(cyclopentadienyl)zirconium dichloride as precursor. The effect of synthesis parameters on the morphology of samples ZrC/MWCNT was studied and the optimal synthesis conditions were selected. The structure and morphology of synthesized hybrid nanomaterials were investigated by X-ray diffraction, scanning and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

We have demonstrated a quantum cascade laser (QCL) with a generation frequency of about 3.8 THz, grown by metal-organic vapor phase epitaxy. The multilayer heterostructure for QCLs consists of 185 repetitions of an active module containing four GaAs/Al0.15Ga0.85As quantum wells. The threshold current and threshold voltage of the fabricated QCL were 2.25 kA/cm2 and 19.7 V, respectively. The QCL oscillations were carried out in the multimode regime, and the detection of terahertz radiation continued with an increase in the laser temperature up to 60 K. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study of factors affecting the thickness of transition (interface) layers in stressed InAs/GaSb superlattices during growth by MOCVD method. It is shown that the thicknesses of the interface layers between InAs and GaSb are practically independent of the growth temperature. The thickness of the interface layers is influenced by the direction of switching the layer growth. The smallest thickness of 1.2–1.4 nm of the interface layer InAs/GaSb was obtained for the direction of growth switching from GaSb to InAs. [ABSTRACT FROM AUTHOR]

Artificial neural networks (ANNs) are a type of machine learning model that are designed to mimic the structure and function of biological neurons. They are particularly well-suited for tasks such as image and speech recognition, natural language processing, and prediction tasks. The success of an ANN in modeling a particular dataset depends on factors such as the size and quality of the dataset, the complexity of the model, and the choice of training algorithms. High representation rate of a system in the data set can improve the performance of the ANN model. The study we described is focused on using artificial neural networks (ANNs) to model temperature-dependent photoluminescence (PL) characterization of GaN epilayers grown on patterned sapphire substrates (PSS) using the metalorganic chemical vapor deposition (MOCVD) technique. The ANN model is trained using temperature and wavelength as input parameters and intensity as the output parameter, with the goal of accurately predicting the PL intensity of the GaN epilayer as a function of temperature and wavelength. The model is trained using a large set of experimental data and then tested using data that was not presented to the model during training. The results of the study suggest that ANN modeling methodology is an effective and accurate way of modeling temperature-dependent PL of GaN epilayers grown on PSS. The results of the study suggest that ANN modeling methodology can be used to accurately predict the temperature-dependent PL of GaN epilayers grown on PSS. This means that it may be possible to reduce the number of required experimental measurements by using the ANN model to predict PL intensity at different temperatures, based on a smaller set of experimental measurements. This could potentially save time and resources, while still obtaining accurate information about the optical behavior of GaN-based materials at different temperatures. [ABSTRACT FROM AUTHOR]

Deep-level transient spectroscopy (DLTS) measurements were performed on HgCdTe heterostructure photodiode grown by metal-organic chemical vapor deposition (MOCVD) on GaAs substrate. In order to extract defects from individual layers of the heterostructure, three consecutive etchings were performed. In the first experiment, the N+/T/p/T/P+/n+ structure was chemically etched to the N+ bottom contact to obtain a mesa-type detector. Six localized defects were extracted across the entire photodiode. In the second experiment, the bottom contact was made to the p-type absorber. Two localized defects were found in the p/T/P+/n+ structure. In the third experiment, the top layers were removed and N+/T/p type detector was made—the cap contact was made to the p-type absorber, the bottom to the N+ layer. Five defect levels were identified, three of which overlap with the first experiment. A deep-trap level located at 183 meV above the top of the valence band was identified within the absorber bandgap. This energy coincides with the activation energy determined from the Arrhenius plot for the dark currents. A defect at the level of ∼0.5Eg suggests that the dark current at low reverse bias voltage is dominated by the Shockley–Read–Hall (SRH) mechanism. [ABSTRACT FROM AUTHOR]

Experimental results are reported for a medium-wavelength infrared (MWIR) HgCdTe photodetector designed in a joint laboratory run by VIGO Photonics S.A. and the Military University of Technology. The parameters of the MWIR detectors fabricated with HgCdTe heterostructures were studied. Advances in the metal–organic chemical vapor deposition (MOCVD) technique enable the growth of HgCdTe epilayers with a wide range of composition and doping, used for uncooled infrared detectors. Device-quality HgCdTe heterostructures were deposited on 2-inch-diameter, low-cost (100) GaAs substrates. The heterostructures obtained were examined measuring the spectral response and current–voltage characteristics in different temperatures. Our intention here was to determine the relationship between electrical and optical results, using thermal analysis of dark current properties and photocurrent and spectral characteristics. The appearance of an additional signal source in certain ranges of reverse voltages was examined. Comparative analysis of the electrical and electro-optical characterization enabled us to isolate the photocurrent originating from different layers of the detector structure. Automated measurement techniques make it possible to correlate current responsivity with current–voltage curves measured as a function of temperature in a range from 10 K to 300 K with ±0.05 K resolution without human exertion. LabVIEW-aided data acquisition enables the averaging of each characteristic several hundred times, eliminates random and human errors, and decreases measurement uncertainty. [ABSTRACT FROM AUTHOR]

Spray parameters were fixed to depositing a MCrAlY coating by HVOF process on IN-708 substrate. The deposited coatings exhibited a microstructure with characteristic splats and β and γ phases. An MOCVD process was subsequently carried out to deposit a thin alumina layer on the sprayed MCrAlY coating. Cyclic oxidation tests were conducted at high temperature on the alumina/MCrAlY coating system. Both SEM and XRD analyses were used to characterize the thermally grown oxide after cyclic oxidation. A kinetic analysis was done to determinate the behaviour of the alumina/MCrAlY coating system during oxidation. [ABSTRACT FROM AUTHOR]

Heavily Si-doped GaN epitaxial layers (n+GaN) have been grown on semi-insulating 6H-SiC substrate by metal–organic chemical vapor deposition at 1030°C using H2 and N2 as carrier gases. Thin film characterization results demonstrated that n+GaN grown in N2 carrier gas has superior morphological and crystalline quality to that grown in H2. The surface morphology of n+GaN grown with N2 carrier gas is insensitive to the growth rate and SiH4 flow with Si doping concentration up to 1.1 × 1020/cm3. Secondary ion mass spectrometry analysis confirmed that C and O impurity levels in n+GaN are one order of magnitude lower with N2 carrier gas than with H2. The results thus indicate that 100% N2 could be a better carrier gas candidate to enable a broader process window for future HEMT S/D n+GaN selective area epitaxial process applications. [ABSTRACT FROM AUTHOR]

The structure of trimethylplatinum(IV) iodide [(CH3)3PtI]4 (I) (CIF file CCDC no. 22330007) is refined. The structure of the synthesized for the first time trimethylplatinum(IV) complex with tridentate N,N,O-iminoketonate [(CH3)3Pt(C9H17N2O)] (II) is determined by X-ray diffraction (XRD) (CIF file CCDC no. 22330008). The purity of the isolated phases is confirmed by elemental analysis and IR and NMR spectroscopy. The thermal behavior of complex II is studied by thermogravimetry. The energies of ionization and fragmentation of the molecules of complex II leading to the formation of the most stable fragment [(CH3)3Pt]+ are estimated by quantum-chemical calculations. Complex II is tested in the MOCVD processes. The Pt films with the pronounced (111) texture and particle sizes about 100 nm are prepared on Si plates in the presence of oxygen. [ABSTRACT FROM AUTHOR]

Optimized photoconverters for operation under high-power laser radiation in the green-red spectral range based on MOCVD-grown GaInP/GaAs heterostructures are fabricated. The Au(Ge)/Ni/Au and Pd/Ge/Au contact systems have been studied to form the front contact grid of devices. As a result, the laser photoconverter with a Pd/Ge/Au contact showed an efficiency of more than 50% up to an incident radiation power density of 30 W/cm2 with a maximum value of 54.4% under 7 W/cm2 for laser line with wavelength of 600 nm. [ABSTRACT FROM AUTHOR]

β-Ga2O3 thin films with both a 45 nm Si-doped conductive epilayer and unintentionally doped epilayer were grown on c-plane sapphire substrate by metalorganic chemical vapor deposition. β-Ga2O3 based metal–oxide–semiconductor field-effect transistors (MOSFETs) were fabricated with gate recess depths of 20 nm and 40 nm (it indicated gate depth with 70 nm and 50 nm, respective), respectively, and without said recessing process. The conductivity of β-Ga2O3 epilayers was improved through low in situ doping using a tetraethoxysilane precursor to increase MOSFET forward current density. After recessing, MOSFET operation was transferred from depletion to enhanced mode. In this study, the maximum breakdown voltage of the recessed 40 nm transistor was 770 V. The etching depth of a recessed-gate device demonstrates its influence on device electrical performance. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated Ga2O3-based power MOSFETs grown on c-plane sapphire substrates using in-situ TEOS doping for the first time. The β-Ga2O3:Si epitaxial layers were formed by the metalorganic chemical vapor deposition (MOCVD) with a TEOS as a dopant source. The depletion-mode Ga2O3 power MOSFETs are fabricated and characterized, showing the increase of the current, transconductance, and breakdown voltage at 150 °C. In addition, the sample with the TEOS flow rate of 20 sccm exhibited a breakdown voltage of more than 400 V at RT and 150 °C, indicating that the in-situ Si doping by TEOS in MOCVD is a promising method for Ga2O3 power MOSFETs. [ABSTRACT FROM AUTHOR]

Remote epitaxy, which was discovered and reported in 2017, has seen a surge of interest in recent years. Although the technology seemed to be difficult to reproduce by other labs at first, remote epitaxy has come a long way and many groups are able to consistently reproduce the results with a wide range of material systems including III-V, III-N, wide band-gap semiconductors, complex-oxides, and even elementary semiconductors such as Ge. As with any nascent technology, there are critical parameters which must be carefully studied and understood to allow wide-spread adoption of the new technology. For remote epitaxy, the critical parameters are the (1) quality of two-dimensional (2D) materials, (2) transfer or growth of 2D materials on the substrate, (3) epitaxial growth method and condition. In this review, we will give an in-depth overview of the different types of 2D materials used for remote epitaxy reported thus far, and the importance of the growth and transfer method used for the 2D materials. Then, we will introduce the various growth methods for remote epitaxy and highlight the important points in growth condition for each growth method that enables successful epitaxial growth on 2D-coated single-crystalline substrates. We hope this review will give a focused overview of the 2D-material and substrate interaction at the sample preparation stage for remote epitaxy and during growth, which have not been covered in any other review to date. [ABSTRACT FROM AUTHOR]

The effects of pre-metallization of the growth surface on film stress and structural properties of undoped and Ge-doped AlxGa1−xN (x ~ 0.5–0.6) epilayers grown by metal–organic chemical vapor deposition (MOCVD) on 500 nm-thick hydride vapor-phase epitaxy (HVPE) AlN/sapphire templates were investigated. AlxGa1−xN typically grows under compressive stress on the AlN templates due to its larger lattice parameter, which can lead to increased surface roughness and V-pits in undoped and Ge-doped AlxGa1−xN. The introduction of the group III sources in the growth ambient for a short period of time (5 s) prior to the addition of NH3 induced a tensile growth stress in the AlxGa1−xN, as measured by in situ wafer curvature measurements, which correlated with an improvement in the surface morphology. However, the pre-metallization was also observed to result in the deposition of a carbon-rich layer at the AlxGa1−xN/AlN interface and an increased density of screw-type dislocations as measured by post-growth x-ray diffraction. By utilizing a pre-metallization step with a lower AlxGa1−xN growth rate, it was possible to eliminate the carbon interfacial layer and maintain low surface v-pitting and threading dislocation density in Ge-doped AlxGa1−xN. The results provide insight into the impact of pre-metallization on the AlxGa1−xN/AlN interface and the structural properties of the layers. [ABSTRACT FROM AUTHOR]

The spectral sensitivity change of a silicon photodiode with its temperature is analyzed in the article. This research area is relevant because silicon photodiodes are used as sensitive elements in temperature control systems of the vapour-phase epitaxy process. Technical characteristics of the obtained semiconductor devices are mostly determined by the quality of heterostructures used for their manufacture. The optical pyrometry method is used for the surface temperature precise control of the A3B5 solid solutions active layers during metalorganic chemical vapour deposition (MOCVD). Since the surface relief and parameters during deposition change significantly, classical pyrometry leads to significant measurement errors, so the pyrometry method with radiation compensation is used. This method combines the wafer surface radiation measurement and its reflectivity. This allows to determine the surface temperature true value, the layer thickness and the heat distribution uniformity on the wafer in real time. However, for high precision, it is necessary to take into account the temperature coefficient of the silicon photodiode ampere-watt sensitivity change. The basics of MOCVD technology are discussed in this article. The features of the epitaxy process in the reactor with high-precision temperature control are highlighted. The analytical and empirical study of change in silicon photodiode ampere-watt sensitivity and its effect on measurement accuracy are given. The research results improve the accuracy of real temperature measurement using pyrometric parameter control systems in MOCVD technology and help to understand and to take into account the influence of temperature factors on measurement accuracy to improve this technology. [ABSTRACT FROM AUTHOR]

Al0.9Ga0.1As/GaAs distributed Bragg reflector (DBR) structure with different doping type and doping concentrations was grown by metal organic chemical vapor deposition (MOCVD), and the material and optoelectronic characteristics were studied by X-ray diffraction (XRD) rocking curves, scanning electron microscopy (SEM), electrochemical capacitance–voltage (ECV) profiling, and low-temperature photoluminescence spectroscopy. Results showed that period thickness of AlGaAs and GaAs layers was reduced by the CCl4 doping process and that the AlGaAs layer achieved a higher doping concentration than the GaAs materials. Additionally, there exist four recombination mechanisms in the structure of fabricated Al0.9Ga0.1As/GaAs DBR with varied doping. The recombination between the electrons of the conduction band and holes of the valence band in the 2.09 × 1018 cm−3 Si-doped GaAs layers dominated the photoluminescence in the lower temperature range, while recombination in the 1.08 × 1018 cm−3 C-doped GaAs layers gradually became the dominant factor at near room temperature. [ABSTRACT FROM AUTHOR]

GaAs-on-Si templates with two different dislocation filter layers (DFLs) were grown at 550 °C low-temperature (LT)-DFL and 660 °C high-temperature (HT)-DFL using metal organic vapor-phase epitaxy and the effects of the growth temperature were studied. The threading dislocation density (TDD) values of LT-DFL and HT-DFL were 5.2 × 107 cm−2 and 1.5 × 107 cm−2, respectively. The 1.5 × 107 cm−2 of TDD in HT-DFL is reduced by almost one order compared to the 1.2 × 108 cm−2 of that in the control sample without DFLs. The annihilation process was mainly observed in the HT-DFL by a transmission electron microscope, resulting in a lower TDD. The 500-nm-thick GaAs bulk layer and InAs QDs were regrown on GaAs-on-Si templates and the optical properties were also evaluated by photoluminescence (PL). The highest PL peak intensity of the HT-DFL indicates that less non-radiative recombination in both the GaAs bulk and QDs occurred due to the reduced TDD. The GaAs p–i–n diodes were also fabricated to analyze the bulk leakage (JB) and the surface leakage current. The JB of HT-DFL shows the lowest value of 3.625 × 10–7 A/cm−2 at applied bias voltage of 1 V, which is 20 times lower than the JB of the control sample without DFLs. This supports that the high-temperature growth of DFL can make a good performance GaAs device on Si. [ABSTRACT FROM AUTHOR]

Recently, the number of projects has grown connected with the application of high-temperature superconductors (HTSC) with exceptionally high current-carrying characteristics in strong magnetic fields. However, the thickness of the RBa2Cu3O7–x (R = REE, Y) superconducting layer is only 1–2% of the thickness of HTSC tape. Increasing the current-carrying characteristics owing to the thickness of the conducting layer is a promising approach. The fundamental problem of crystallite formation of a-oriented crystallites prevents the development of this approach. Such crystallites do not carry superconducting current along the substrate tape and interfere with the growth of c-oriented crystallites. This review presents existing methods of suppression of a-oriented growth, the basis of the creation of HTSC materials, and prospects of obtaining HTSC materials with high current-carrying characteristics. [ABSTRACT FROM AUTHOR]

InGaAs/GaAs single quantum wells (QWs) were grown on oriented GaAs substrates by metal-organic chemical vapor deposition (MOCVD). Photoluminescence (PL) measurement at room temperature was applied to characterize the optical properties of QWs. The effects of offcut substrates, growth temperature, growth rate and V/III ratio on optical properties were investigated. For 1060-nm InGaAs/GaAs quantum wells, the results show that when the growth temperature is 600°C, the V/III ratio is 43, and the growth rate is 1.15 µm/h, the quality of the quantum well is better. With the decrease of growth temperature, the PL intensity increased significantly. When the temperature is 600°C, the PL intensity is 121% and 52% higher than the other two samples, respectively. FWHM was reduced by 35% and 46% compared with the other two samples, respectively. When the growth rate increased, the PL intensity enhanced 75%, while the FWHM decreased 5%. It can be found that the FWHM decreased greatly and a blueshift occurred with the increase of the growth rate proving that the crystal quality is greatly improved. Increased V/III ratio can improve the growth quality and optical characteristics of InGaAs/GaAs QWs. The wavelength of samples showed a redshift with increased V/III ratio. [ABSTRACT FROM AUTHOR]

Peculiar and unique growth mechanisms involved in semiconductor nanowires (NWs) pave the way to the achievement of new crystallographic phases and remarkable material properties, and hence, studying polytypism in semiconductor NWs arouses a strong interest for the next generation of electronic and photonic applications. In this context, the growth of ZnS nanowires has been investigated, as bulk ZnS compound exhibits numerous unstable polytypes at high temperatures, but their stable occurrence is highly anticipated in a nanowire due to its special quasi-dimensional shape and growth modes. In this work, the idea is to provide a change in the growth mechanism via the physical state of catalyst droplet (liquid or solid) and hence, study the induced structural modifications in ZnS nanowires. The HRTEM images of VLS (via liquid alloyed catalyst) grown ZnS NWs show periodic stacking faults, which is precisely identified as a stacking sequence of cubic or hexagonal individual planes leading to an astonishing 15R crystal polymorph. This crystallographic phase is observed for the first time in nanowires. Contrastingly, NWs grown with VSS (via solid catalyst) show crystal polytypes of zinc blende and wurtzite. We calculate and discuss the role of cohesive energies in the formation of such ZnS polytypes. Further, we present the selection rules for the crystallization of such 15R structure in NWs and discuss the involved VLS and VSS growth mechanisms leading to the formation of different crystal phases. [ABSTRACT FROM AUTHOR]

Contact between two-dimensional (2D) transition metal dichalcogenides and certain metals (Au, Pd, Ti, or Pt) results in strong Fermi-level pinning and high resistance. Furthermore, to construct a high-performance device, accurate measurement of the contact resistance and Schottky barrier height (SBH) is crucial. In this study, the SBH and the resistance of a 2H phase few-layer molybdenum telluride (2H–MoTe2) film, which was grown by metal organic chemical vapor deposition, and a Ti/Au electrode were determined by analyzing the high-temperature thermal transmission properties and the transmission line method, respectively. The carrier mobility, ON/OFF ratio, SBH, and contact resistance of the few-layer MoTe2 device, which has p-type behavior with Ti/Au electrode, were found to be 53.7 cm2 V−1 s−1, 3.44 × 106, 163 meV, and 10.2 M Ω , respectively. [ABSTRACT FROM AUTHOR]

This work has investigated the effects of etching treatment on as-grown and regrown GaN-on-GaN structures intended for vertical p-n power device applications. Surfaces of thick unintentionally doped (UID) GaN layers, grown homoepitaxially via metal-organic chemical vapor deposition on freestanding GaN bulk substrates, were subjected to RF-plasma dry etching, and additional layers of UID-GaN/p-GaN were then grown. The as-grown and regrown structures were examined in cross section using transmission electron microscopy. Two different types of etching treatment were used, fast-etch-only and multiple etches with decreasing power. Images of the fast-etch-only devices clearly showed the GaN-on-GaN interface at the etched location, and low device breakdown voltages were measured (reverse bias in the range of 45–95V). In comparison, no interfaces were visible in devices after multiple etching steps, and the corresponding device breakdown voltages were markedly higher (reverse bias ~1200–1270V). These results emphasize the importance of optimizing surface etching techniques for avoiding degraded performance in GaN-on-GaN power devices that require GaN regrowth. [ABSTRACT FROM AUTHOR]

A pulsed atomic-layer epitaxy growth technique has been introduced to substantially diminish the induced strain and oxygen incorporation on aluminium nitride films grown at standard pressure by metal organic chemical vapour deposition. The qualities of the as-deposited aluminium nitride films were studied by varying the aluminium nitride nucleation layer growth temperature at 700°C, 800°C, 900°C, 1000°C and 1100°C, respectively. The compressive strain inside the as-deposited aluminium nitride films, induced by the hetero-epitaxial growth on sapphire, was investigated through Raman spectroscopy by focusing on the evolution of E2 (high) peak frequency, where almost stress-free aluminium nitride films were attained at nucleation layer growth temperature of 1100°C. Then, the correlation between luminescence defect and level of foreign impurities respective to the varied nucleation layer growth temperatures were also systematically analysed through photoluminescence spectroscopy and x-ray photoelectron spectroscopy, respectively. [ABSTRACT FROM AUTHOR]

This paper summarizes progress in metal organic chemical vapour deposition (MOCVD) technology achieved in recent years at the Institute of Applied Physics, Military University of Technology and VIGO System S.A. MOCVD with a wide range of composition and donor/acceptor doping and without post-growth annealing is a very convenient tool for the deposition of HgCdTe epilayers used for uncooled infrared detectors. Particular attention is focused on: surface morphology improvement, doping issues, diffusion processes during growth study, substrate issues, crystallographic orientation selection. In this respect, MOCVD technology improvement influencing IR detector parameters is shown. CdTe buffer layer deposition allows HgCdTe heterostructure growth on GaAs substrates. Theoretical modelling using APSYS platform supports designing and better understanding of the carrier transport mechanism in detector's structures. Secondary ion mass spectrometry profiles allows to compare projected and obtained structures and revealed diffusion processes of the elements. A wide range of different types of infrared detectors operating at high operating temperature conditions has been constructed: photoresistors, non-equilibrium photodiodes, dual-band photodiodes, barrier and multiple detectors. The methodical research efforts contributed to the time constant reduction are important in many detector applications. Future challenges and prospects are also discussed. [ABSTRACT FROM AUTHOR]

In this work, (-2 0 1) β-Ga2O3 films are grown on GaN substrate by metal organic chemical vapor deposition (MOCVD). It is revealed that the β-Ga2O3 film grown on GaN possesses superior crystal quality, material homogeneity and surface morphology than the results of common heteroepitaxial β-Ga2O3 film based on sapphire substrate. Further, the relevance between the crystal quality of epitaxial β-Ga2O3 film and the β-Ga2O3/GaN interface behavior is investigated. Transmission electron microscopy result indicates that the interface atom refactoring phenomenon is beneficial to relieve the mismatch strain and improve the crystal quality of subsequent β-Ga2O3 film. Moreover, the energy band structure of β-Ga2O3/GaN heterostructure grown by MOCVD is investigated by X-ray photoelectron spectroscopy and a large conduction band offset of 0.89 eV is obtained. The results in this work not only convincingly demonstrate the advantages of β-Ga2O3 films grown on GaN substrate, but also show the great application potential of MOCVD β-Ga2O3/GaN heterostructures in microelectronic applications. [ABSTRACT FROM AUTHOR]

A new method for depositing carbon films by the thermal decomposition of carbon tetrachloride (CCl4) in a hydrogen flux in a reactor for metal-organic chemical vapor deposition (MOCVD) at atmospheric pressure is developed. From the results obtained by Raman spectroscopy, it can be conceived that the carbon layers produced by this method are the disordered nanocrystalline graphite. It is shown that such carbon layers can be used in the technological cycle of the production of gallium-arsenide optoelectronic device structures (among them spin light-emitting diodes with a CoPt injector). [ABSTRACT FROM AUTHOR]

The effect of annealing temperature and time on the luminescence intensity of the InGaN/GaN heterostructure subjected to ion beam etching was studied. We show that annealing at a temperature of 1100°C makes it possible to eliminate the radiation defects in the GaN layers that arise in the etching process with a focused Ga+ ion beam (30 keV). [ABSTRACT FROM AUTHOR]

This paper reports the structural and photoluminescent study results of heterostructure with short-period InAs/GaSb superlattice grown by MOCVD with 8/10 ML period thickness. The photoluminescence spectra was observed in the range of 3–5 μm with intensity peak at 3.8 μm. SL minibands theoretical calculation with a high accuracy confirmed the experimental data obtained. This indicates that the specified structural parameters match the chosen growth conditions. [ABSTRACT FROM AUTHOR]

Bis-(morpholinodithiato-s,s′)-Cu-Zn was synthesized as a single solid source precursor and characterized using particle-induced x-ray emission (PIXE), Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Cu-Zn-S thin film was deposited on sodalime glass substrate using metal organic chemical vapor deposition (MOCVD) technique at temperatures ranging from 360°C to 450°C. The thin films were characterized using Rutherford backscattering spectroscopy (RBS), x-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and four-point probe technique. PIXE of the precursor confirmed the presence of the expected elements that can lead to deposition of Cu-Zn-S thin film while FTIR confirmed that the organic ligands were attached to the metals. DSC showed that the precursor is thermally stable and can pyrolyze at temperature between 340°C and 460°C. RBS analysis of the films showed that there was no substantial deposition at 360°C while other films showed various stoichiometry and thickness. XRD analysis of the films showed that films deposited at 360°C and 380°C are amorphous, while those deposited between 400°C and 450°C showed peaks, in which the crystal size decreased as the deposition temperature increased. The SEM micrographs showed that the morphology of the films is temperature dependent and as deposition temperature increased larger secondary grains dissociated into smaller grains that are closely packed, without cracks and holes. Optical characterization showed that the films exhibited high transmittance, which fairly increased as the deposition temperature increased. A direct band gap value between 2.49 eV and 2.92 eV was obtained as deposition temperature increased. Urbach energy also increased from 0.87 eV to 1.51 eV, while the steepness parameter decreased as the deposition temperature increased. The electrical characterization showed that the resistivity of the films decreased as the deposition temperature increased while the I–V plot showed a rectifying character. [ABSTRACT FROM AUTHOR]

The volatile palladium(II) and copper(II) {O,N}-coordinated bis-chelate complexes of a new type, Pd(dmht)2 and Cu(dmht)2, where dmht = 1,1,1-trifluoro-2-(2,2-dimethylhydrazone)pentan-4-onato, were synthesized, purified and identified by elemental analysis, IR and NMR spectroscopy and mass spectrometry. The thermal behavior of the complexes in the condensed phase was studied by TG-DTA and DSC methods. The temperature dependences of saturated vapor pressure were measured for Pd(dmht)2 and Cu(dmht)2 in the temperature ranges ΔT = (343–388) K (flow method) and ΔT = (321–390) K (flow and Knudsen effusion method), respectively. The ketohydrazonate complexes characterized by close enthalpy and entropy of melting and sublimation processes and the highest volatility among the related compounds. The new complexes were successfully used as precursors for metal-organic chemical vapor deposition of mono- and bimetallic thin films onto Si (100) substrates at the reducing atmosphere. [ABSTRACT FROM AUTHOR]

The processes of palladium deposition on various high-porosity carbon matrices (Sibunit, CMK-3) have been studied. Mesostructured carbon material CMK-3 was synthesized using a silicate template of SBA-15 type. Pd nanoparticles were loaded onto carbon matrices by metalorganic chemical vapour deposition (MOCVD) method using palladium(II) acetylacetonate precursor. Bimetal Au–Pd systems were synthesized by autoclave reduction of gold(III) chloride complexes on Pd-containing carbon matrices. Structure of the obtained composite particles was studied by electron microscopy and X-ray diffraction. The average diameter of Pd particles on Sibunit is about 10, and 5–6 nm on CMK-3. The catalytic activity of the synthesized materials was studied in the reaction of furfural diethyl acetal (FDEA) hydrogenation, using gas–liquid chromatographic analysis. There is significant difference in catalytic activity of MOCVD-Pd/C compared to conventional impregnated Pd/C systems: the hydrogenation rate is 3–6 times higher with MOCVD-derived catalysts. Introducing Au into a MOCVD-Pd/C catalyst increases the hydrogenation rate threefold. Considerable difference in the composition of hydrogenation products was observed between these differently prepared catalysts. [ABSTRACT FROM AUTHOR]

The effects of surface treatment processes of p-GaAs (001) on the photocurrent properties of Cs/p-GaAs (001) obtained during Cs evaporation have been investigated using a metal-organic chemical vapor deposition (MOCVD)-negative electron affinity (NEA) multichamber system comprising an MOCVD chamber, load-lock chamber, and NEA surface-activation chamber. Samples were transferred from the MOCVD chamber to the NEA surface-activation chamber without air exposure. Moreover, the air exposure time before Cs evaporation was controlled by opening the load-lock chamber. Almost the same peak photocurrents were observed for samples fabricated using only tertiarybutylarsine or H2 supply after thermal cleaning of the p-GaAs substrate. However, tertiarybutylphosphine supply after thermal cleaning of the p-GaAs substrate degraded its surface morphology and decreased its peak photocurrent. The peak photocurrent decreased monotonically with lengthening air exposure time. Moreover, the start time of the rise in photocurrent was delayed monotonically with lengthening air exposure time. These experimental results reveal that the surface treatment process of p-GaAs (001) applied before Cs evaporation is an important factor controlling the photocurrent properties. [ABSTRACT FROM AUTHOR]

Ga-doped Zn0.7-xMg0.3O thin films were deposited on glass substrates at 350 °C by metal-organic chemical vapor deposition using an ultrasonic nebulization technique to transport the source precursors, and the effects of the Ga-doping concentration were investigated. The films with Ga-doping concentrations less than 5 mol% grew with [001] preferred orientation perpendicular to the substrate surface and were composed of large crystallites. At Ga content greater than 5 mol%, the films grew with random orientation and very small crystallite size. The charge carrier concentration in the films increased rapidly up to 4 mol% Ga and then decreased gradually with further increases in the Ga-content. The film resistivity decreased with increasing Ga-content up to 4 mol% due mainly to the increase in charge carrier concentration. Then, the resistivity increased gradually with increasing Ga-content due to the decrease in mobility. The lowest resistivity of the Ga-doped Zn0.7-xMg0.3O thin film was 3.8 × 10−1 Ωcm at the Ga doping concentration of 4 mol%. The mean transmittance in the visible range was more than 85% in all films. The optical band gap of the films increased with increasing Ga-doping concentration up to 5 mol% due to the Burstein-Moss effect. [ABSTRACT FROM AUTHOR]

The home-designed metal organic chemical vapor deposition (MOCVD) system was applied to prepare the Gd0.5Y0.5Ba2Cu3O7-δ (GdYBCO) films at a high deposition rate in order to improve the production efficiency and reduce the preparation cost of high temperature superconducting tapes. Based on a simple self-heating method, the distance between the shower head and the substrate surface can be reduced effectively to increase the concentration of metal organic sources on the substrate surface, which can commendably improve the deposition rate of GdYBCO films and the utilization ratio of metal organic sources. At last, the GdYBCO films were successfully prepared on the LaMnO3 template at the high deposition rate of 1 μm/min by the MOCVD process based on the simple self-heating method and the critical current (Ic) was more than 220 A/cm-width (77 K, 0 T), corresponding to the critical current density (Jc) more than 4.4 MA/cm2 (77 K, 0 T). [ABSTRACT FROM AUTHOR]

The effect of the growth temperature and the flow of trimethylgallium on the process of selective epitaxy of gallium nitride in windows of submicron size have been studied. The conditions under which homogeneous nucleation and coalescence of nuclei are combined with a low growth rate are determined. The steady growth of variously oriented gallium nitride strips with a height of 50 nm and a width of 600 nm was realized. [ABSTRACT FROM AUTHOR]

The effects of Gd content on crystalline orientation, microstructure and superconductivity of GdxY1−xBa2Cu3O7−δ (GdYBCO) films were systematically investigated. By varying the Gd content in the liquid precursor without changing the total amount of rare earth elements, series of GdYBCO films with x values of 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 were fabricated by metal organic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis revealed that Gd introducing could restrain the formation of CuYO2 phase, but induce a-axis growth of GdYBCO film. The increase of x from 0 to 0.5 leads to enhancing critical current density at self-field and 77 K (Jcsf) from 1.8 to 2.8 MA·cm−2, which benefits from the decrease in CuYO2 impurities and improvement of in-plane texture from 5.0° to 4.3°. However, raising x from 0.5 to 1.0 gives rise to abundant a-axis growth of film and degradation of in-plane texture from 4.3° to 5.4°, consequently resulting in the decrease of Jcsf from 2.8 to 0.8 MA·cm−2. Even though Jcsf has not varied monotonically, the critical transition temperature of GdYBCO films linearly increases from 90.75 to 92.25 K and the in-field performance at magnetic field (B) of 0-1.1 T and 77 K as well as B parallel to film normal is also superior with Gd content increasing. [ABSTRACT FROM AUTHOR]

Re-W nanoparticles are deposited onto multiwalled carbon nanotubes by the metal organic chemical vapor deposition technique. A mixture of dirhenium decacarbonyl and tungsten hexacarbonyl is used as a precursor. Nanoparticles of hybrid materials are studied by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray phase analysis. It is found that in a wide range of ratios of the precursors (dirhenium decacarbonyl and tungsten hexacarbonyl), the crystalline component is a Re-W phase, and the morphology of the nanoparticles is the same as that of the nanodendrites. [ABSTRACT FROM AUTHOR]

Clinoptilolite-supported TiO2 (TiO2/CPMOCVD) has been synthesized by metal organic chemical vapor deposition method (MOCVD). Titanium precursor was evaporated at 110 °C under nitrogen flow rate to promote the surface interaction between titanium species and clinoptilolite. The effect of titanium precursor on the crystalline structure and the surface area of clinoptilolite were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), transformed infrared spectroscopy (FT-IR), Raman spectroscopy, and Brunauer-Emmett-Teller measurement. XRD and SEM results indicate that TiO2 precursor interacted with the support, decreasing the crystallinity of the clinoptilolite. The analysis by FT-IR spectroscopy further confirms that the titanium species were bound to clinoptilolite through Ti-O-Si bonds. The TiO2/CPMOCVD catalyst showed a mesoporous structure with the distribution of pores in several dimensions 3.7-7.1 nm, with high specific surface area (~ 471 m2/g). MOCVD improved the adsorption capacity of the catalyst surface towards the pollutants. TiO2/CPMOCVD particles turn yellow after adsorption of salicylic acid. The development of the yellow color is a clear indication of the formation of charge transfer titanium (IV) salicylate surface complex. Photocatalytic decomposition of SA in aqueous solution was carried out using TiO2/CPMOCVD. Experimental results revealed that TiO2/CPMOCVD required shorter irradiation time (120 min) for complete decomposition of SA than commercial P25 Degussa and TiO2/CPimp (clinoptilolite-supported TiO2 using impregnation method). The TiO2/CPMOCVD can be recycled at least four times without loss in activity, indicating their magnificent stability. [ABSTRACT FROM AUTHOR]

Fe-containing nanoparticles have been grown for the first time on the surface of multiwalled carbon nanotubes by metalorganic chemical vapor deposition using iron acetylacetonate, Fe(acac)3,as a precursor. The resultant hybrid nanomaterial has been characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the synthesized material consists of multiwalled carbon nanotubes whose surface is decorated with iron nanoparticles. [ABSTRACT FROM AUTHOR]

We employ a simple two-step growth technique to grow large-area 1550-nm laser structures by direct hetero-epitaxy of III-V compounds on patterned exact-oriented (001) silicon (Si) substrates by metal organic chemical vapor deposition. Densely-packed, highly uniform, flat and millimeter-long indium phosphide (InP) nanowires were grown from Si v-grooves separated by silicon dioxide (SiO) stripes with various widths and pitches. Following removal of the SiO patterns, the InP nanowires were coalesced and, subsequently, 1550-nm laser structures were grown in a single overgrowth without performing any polishing for planarization. X-ray diffraction, photoluminescence, atomic force microscopy and transmission electron microscopy analyses were used to characterize the epitaxial material. PIN diodes were fabricated and diode-rectifying behavior was observed. [ABSTRACT FROM AUTHOR]

The influence of the main growth parameters on the growth mechanism and film formation processes during metalorganic vapor-phase epitaxy (MOVPE) of two-dimensional MoS on sapphire (0001) have been investigated. Deposition was performed using molybdenum hexacarbonyl and di- tert-butyl sulfide as metalorganic precursors in a horizontal hot-wall MOVPE reactor from AIXTRON. The structural properties of the MoS films were analyzed by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. It was found that a substrate prebake step prior to growth reduced the nucleation density of the polycrystalline film. Simultaneously, the size of the MoS domains increased and the formation of parasitic carbonaceous film was suppressed. Additionally, the influence of growth parameters such as reactor pressure and surface temperature is discussed. An upper limit for these parameters was found, beyond which strong parasitic deposition or incorporation of carbon into MoS took place. This carbon contamination became significant at reactor pressure above 100 hPa and temperature above 900°C. [ABSTRACT FROM AUTHOR]

We report on the effect of growth polarity and pulsed or $$\delta $$ -doped growth mode on impurity incorporation in metalorganic chemical vapor deposition-grown GaN. In Ga-polar orientation, up to 12× enhancement in Mg concentration for given Mg flow rate is observed, resulting in enhanced p-type conductivity for these samples. In contrast, this enhancement effect is greatly diminished for N-polar samples, falling off with increasing Mg flow and showing maximum enhancement of 2.7× at 30 nmol/min Mg flow. At higher Mg flow rates, Mg incorporation at normal levels did not correspond to p-type conductivity, which may be due to Mg incorporation at nonacceptor sites. Concentrations of C, O, and Si were also investigated, revealing dependence on Mg flow in N-polar pulsed samples. Carbon incorporation was found to decrease with increasing Mg flow, and oxygen incorporation was found to remain high across varied Mg flow. These effects combine to result in N-polar samples that are not p-type when using the pulsed growth mode. [ABSTRACT FROM AUTHOR]

Zinc tin oxide (ZTO) thin films, with zinc acetate and tributyltin chloride as raw materials, were deposited on glass substrates by the method of metal organic chemical vapor deposition (MOCVD). The crystallization, microstructure and optical properties were investigated by scanning electronic microscope (SEM), X-ray diffraction (XRD) and ultraviolet-visible (UV-Vis) spectrophotometer. The results show that with the increase in Sn/Zn ratio, the crystal changes from wurtzite to rutile phase. When the ratio reaches 11:18, the intensity of ZnSnO peaks appears to be the strongest and the optical band gap is about 3.27 eV. Calculated by the envelope method, the thickness of the ZTO thin films is 713.24 nm. Measured by UV-Vis spectrophotometer, the transmittance of the ZTO thin films reaches up to 80 % in the wavelength range of 400-1000 nm when the Sn/Zn ratio is 7:18. [ABSTRACT FROM AUTHOR]

We have investigated the optical properties of ZnO nanowires grown by metalorganic chemical vapor deposition (MOCVD) with nitrous oxide (NO) as oxygen precursor. Photoluminescence (PL) and Raman measurements showed the influence of adsorbed molecules on the optical properties. Low-temperature (4 K) PL studies on the surface exciton (SX) at 3.3660 eV elucidated the nature and origin of this emission. In particular, surface treatment by annealing at high temperature under inert gas reduced the emission intensity of SX. Raman vibrational spectra proved that presence of a considerable amount of adsorbed molecules on the surface of ZnO nanowires plays a key role in the occurrence of surface excitons. [ABSTRACT FROM AUTHOR]

222–351 nm AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) are demonstrated, which have been achieved by the development of crystal growth techniques for wide-bandgap AlN and AlGaN. Significant increases in internal quantum efficiency (IQE) have been achieved for AlGaN quantum well (QW) emissions by introducing low-threading-dislocation density (TDD) AlN grown by an NH3 pulsed-flow multilayer growth method. Electron Injection efficiency (EIE) of the DUV LED was significantly increased by introducing multi-quantum barrier (MQB). Light extraction efficiency (LEE) was also improved by using a transparent p-AlGaN contact layer. The maximum external quantum efficiency (EQE) was increased up to 10.8% for a 276 nm DUV LED. [ABSTRACT FROM AUTHOR]

The structural, valence of elements and magnetic characteristics of Ni-implanted AlGaN films, deposited on AlO substrates by metalorganic chemical vapor deposition (MOCVD), were reported. Ni ions were implanted into AlGaN films by Metal Vapor Arc (MEVVA) sources under the energy of 100 keV for 3 h. The films were annealed at 900 K in the furnace for the transference of Ni ions from interstitial sites to substitutional sites in AlGaN and activating the Ni ions. Characterizations were carried out in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and Vibrating sample magnetometer (VSM), indicating that the films have wurtzite structure without forming a secondary phase after annealing. Ni ions were successfully implanted into substitutional sites of AlGaN films and the chemical bonding states of Ni is Ni-N. The apparent hysteresis loops prove the films exhibited ferromagnetism at 300 K. The room temperature (RT) M and H obtained were approximately 0.22 emu/g and 32.97 Oe, respectively. From the first-principles calculation, A total magnetic moment of 2.86 μB per supercell is calculated: the local magnetic moment of NiN tetrahedron, 2.38 μB, makes the primary contribution. The doped Ni atom hybridizes with its four nearby N atoms in NiN tetrahedron, then N atoms are spin polarized and couple with Ni atom with strong magnetization, which result in ferromagnetism. Therefore, the p-d exchange mechanism is responsible for ferromagnetism in Ni-doped AlGaN. It is expected that the room temperature ferromagnetic Ni-doped AlGaN films can make it possible to the applications for the spin electric devices. [ABSTRACT FROM AUTHOR]