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Current reports of thermal expansion coefficients (TEC) of two-dimensional (2D) materials show large discrepancies that span orders of magnitude. Determining the TEC of any 2D material remains difficult due to approaches involving indirect measurement of samples that are atomically thin and optically transparent. We demonstrate a methodology to address this discrepancy and directly measure TEC of nominally monolayer epitaxial WSe2 using four-dimensional scanning transmission electron microscopy (4D-STEM). Experimentally, WSe2 from metal-organic chemical vapor deposition (MOCVD) was heated through a temperature range of 18-564 °C using a barrel-style heating sample holder to observe temperature-induced structural changes without additional alterations or destruction of the sample. By combining 4D-STEM measurements with quantitative structural analysis, the thermal expansion coefficient of nominally monolayer polycrystalline epitaxial 2D WSe2 was determined to be (3.5 ± 0.9) × 10-6 K-1 and (5.7 ± 2) × 10-5 K-1 for the in- and out-of-plane TEC, respectively, and (3.6 ± 0.2) × 10-5 K-1 for the unit cell volume TEC, in good agreement with historically determined values for bulk crystals.

Despite recent advances in growth and characterization of GaN:Be, reliable conductive p‐type GaN:Be remains elusive. In this work, GaN is co‐doped with Be and Mg to improve the incorporation and ionization efficiency of both Be and Mg. Be and Mg are found to interact in complex ways rendering GaN:Be,Mg semi‐insulating. Rather than improving Be and Mg incorporation efficiency, there is an apparent mutual inhibition of incorporation when Be and Mg are co‐dopants. Furthermore, photoluminescence measurements indicate that the BeGa acceptor is reduced in particular, relative to the total [Be]. The same effect is not observed for Mg. From this, it is concluded that Mg preferentially incorporates into Ga lattice sites over Be, and excess Be that cannot incorporate into substitutional sites instead occupies interstitial sites. The interstitial Be acts as donor defect, which compensate Mg acceptors. This provides an explanation for the observed reduction in BeGa‐related luminescence intensity (without an associated decrease in [Be]) in GaN:Be with significant [Mg] content. [ABSTRACT FROM AUTHOR]

Beta-phase gallium oxide (β-Ga2O3) is a cutting-edge ultrawide bandgap (UWBG) semiconductor, featuring a bandgap energy of around 4.8 eV and a highly critical electric field strength of about 8 MV/cm. These properties make it highly suitable for next-generation power electronics and deep ultraviolet optoelectronics. Key advantages of β-Ga2O3 include the availability of large-size single-crystal bulk native substrates produced from melt and the precise control of n-type doping during both bulk growth and thin-film epitaxy. A comprehensive understanding of the fundamental growth processes, control parameters, and underlying mechanisms is essential to enable scalable manufacturing of high-performance epitaxial structures. This review highlights recent advancements in the epitaxial growth of β-Ga2O3 through various techniques, including Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Mist Chemical Vapor Deposition (Mist CVD), Pulsed Laser Deposition (PLD), and Low-Pressure Chemical Vapor Deposition (LPCVD). This review concentrates on the progress of Ga2O3 growth in achieving high growth rates, low defect densities, excellent crystalline quality, and high carrier mobilities through different approaches. It aims to advance the development of device-grade epitaxial Ga2O3 thin films and serves as a crucial resource for researchers and engineers focused on UWBG semiconductors and the future of power electronics. [ABSTRACT FROM AUTHOR]

2D materials have received a lot of interest over the past decade. Especially van der Waals (vdW) 2D materials, such as transition metal dichalcogenides (TMDCs), and their heterostructures exhibit semiconducting properties that make them highly suitable for novel device applications. Controllable mixing and matching of the 2D materials with different properties and precise control of the in‐plane twist angle in these heterostructures are essential to achieve superior properties and need to be established through large‐scale device fabrication. To gain fundamental insight into the potential control of these twist angles, 2D heterostructures of tungsten disulfide (WS2) and graphene (Gr) grown by bottom‐up synthesis via metal‐organic chemical vapor deposition (MOCVD) are investigated using a scanning transmission electron microscope (STEM). Specifically, the combination of conventional high‐resolution imaging with scanning nanobeam diffraction (SNBD) using advanced 4D STEM techniques is used to analyze moiré structures. The latter technique is used to reveal the epitaxial alignment within the WS2/Gr heterostructure, showing a direct influence of the underlying Gr layers on the moiré structure in the subsequent WS2 layers. In particular, the importance of grain boundaries (GBs) within the underlying WS2 and Gr layers on the structure of moiré patterns with rotation angles below 2° is discussed. [ABSTRACT FROM AUTHOR]

Large-area epitaxial growth of III-V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1×109cm-2is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm-2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III-V thin films on van der Waals substrates.

This article is aimed at understanding of the complex design of metalorganic chemical vapour deposition ‐grown InGaN‐based red light‐emitting diode (LED) structure. The contribution of different elements of red LED structure to the stress distribution and threading dislocation density (TDD) evolution is theoretically investigated. For this purpose a self‐consistent modeling of the structure growth process is used, taking into account stress‐modulated indium incorporation, mismatch stress relaxation by threading dislocations and V‐pits, and nucleation of new threading dislocations. The simulation results, consisting of composition, stress, and TDD profiles, are then utilized for modeling of device operation, which allows to analyze contribution of different elements to the heterostructure operation. [ABSTRACT FROM AUTHOR]

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]

The rough morphology at the growth surface results in the non-uniform distribution of indium composition, intentionally or unintentionally doped impurity, and thus impacts the performance of GaN-based optoelectronic and vertical power electronic devices. We observed the morphologies of unintentionally doped GaN homo-epitaxially grown via MOCVD and identified the relations between rough surfaces and the miscut angle and direction of the substrate. The growth kinetics under the effect of the Ehrlich–Schwoebel barrier were studied, and it was found that asymmetric step motions in samples with a large miscut angle or those grown at high temperature were the causes of step-bunching. Meandering steps were believed to be caused by surface free energy minimization for steps with wide terraces or deviating from the [ 1 1 ¯ 00 ] m-direction. [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]

Abstract 2D materials have received a lot of interest over the past decade. Especially van der Waals (vdW) 2D materials, such as transition metal dichalcogenides (TMDCs), and their heterostructures exhibit semiconducting properties that make them highly suitable for novel device applications. Controllable mixing and matching of the 2D materials with different properties and precise control of the in‐plane twist angle in these heterostructures are essential to achieve superior properties and need to be established through large‐scale device fabrication. To gain fundamental insight into the potential control of these twist angles, 2D heterostructures of tungsten disulfide (WS2) and graphene (Gr) grown by bottom‐up synthesis via metal‐organic chemical vapor deposition (MOCVD) are investigated using a scanning transmission electron microscope (STEM). Specifically, the combination of conventional high‐resolution imaging with scanning nanobeam diffraction (SNBD) using advanced 4D STEM techniques is used to analyze moiré structures. The latter technique is used to reveal the epitaxial alignment within the WS2/Gr heterostructure, showing a direct influence of the underlying Gr layers on the moiré structure in the subsequent WS2 layers. In particular, the importance of grain boundaries (GBs) within the underlying WS2 and Gr layers on the structure of moiré patterns with rotation angles below 2° is discussed.

Aluminum nitride (AlN) grown on vertical surfaces can be utilized for the fabrication of advanced piezoelectric microelectromechanical systems (MEMS). The in‐plane motion of the parts of a MEMS element is possible when AlN is deposited on the vertical surfaces of the moving structure. For the best device performance, AlN must have high crystal quality, uniform coverage of the vertical sidewalls, and c‐axis crystalline orientation perpendicular to the plane of a vertical surface. The impact of the surface roughness (Rq) of the vertical sidewalls formed in Si using wet and dry etching methods on the crystal quality, crystallographic orientation, and uniformity of the metalorganic chemical vapor deposited (MOCVD) AlN thin films is studied in this paper. In both cases, AlN films demonstrated full sidewall coverage and grew crystalline in the c‐axis direction. AlN films grown on vertical Si surfaces achieved using anisotropic wet etching are highly crystalline and oriented in [0001] direction, while the films grown on vertical surfaces achieved using dry etching displayed a lower level of alignment with the Si sidewalls. [ABSTRACT FROM AUTHOR]

A dense and smooth aluminium nitride thin film grown on a silicon (111) substrates using pulsed metal–organic chemical vapor deposition is presented. The influence of the pulsed cycle numbers on the surface morphology and crystalline quality of the aluminium nitride films are discussed in detail. It was found that 70 cycle numbers produced the most optimized aluminium nitride films. Field emission scanning electron microscopy and atomic force microscopy images show a dense and smooth morphology with a root-mean-square-roughness of 2.13 nm. The narrowest FWHM of the X-ray rocking curve for the AlN 0002 and 10–12 reflections are 2756 arcsec and 3450 arcsec, respectively. Furthermore, reciprocal space mapping reveals an in-plane tensile strain of 0.28%, which was induced by the heteroepitaxial growth on the silicon (111) substrate. This work provides an alternative approach to grow aluminium nitride for possible application in optoelectronic and power devices. [ABSTRACT FROM AUTHOR]

GaN materials have attracted great interest and have demonstrated remarkable potential in many fields. When growing GaN materials, substrate selection is of great importance. By virtue of their nominally unlimited size, easy removal, and excellent thermal conduction, metal substrates have been suggested as an alternative to the commonly used substrates such as sapphire. GaN growth on metal substrates, however, is still quite rare, and many aspects remain unexplored. This paper uses computational fluid dynamics to perform a three‐dimensional numerical simulation of the GaN‐ MOCVD reaction chamber. We investigated the influence of the graphite containers' rotational velocity and the metal matrix's temperature at various locations. When the pressure within the MOCVD chamber remains constant, increasing the graphite tray's rotational velocity enhances the temperature field distribution within the chamber. However, the flow field becomes unstable when the rotation rate exceeds 1000 rpm. Our findings serve as a crucial benchmark for the future parameter optimization of MOCVD growth of GaN on metals. [ABSTRACT FROM AUTHOR]

iBeam Materials is developing a revolutionary new technology to fabricate large‐area inexpensive sheets of GaN‐based LEDs and devices directly on large‐area metal foils. This new technology is based on using ion‐beam crystal alignment to fabricate templates for epitaxial GaN films on flexible metal foil, that are lattice‐matched, as well as thermally highly conductive and thermally matched to GaN. The ion beam assisted deposition (IBAD) texturing process is used to prepare biaxially aligned films as templates for GaN epitaxy. Epitaxial GaN films have been grown on these engineered flexible metal substrates. We have achieved GaN films of several microns in thickness on polycrystalline metal foils that have typical threading dislocation densities of 4 – 8 x 108/cm2. We then used these epitaxial GaN films on IBAD/polycrystalline metal foil as templates to deposit epitaxial multi‐quantum well light emitting diode (LED) InGaN structures. InGaN LED devices were successfully fabricated and patterned into MicroLED arrays on metal foil. We observe photoluminescence from these LED structures with 70% of the intensity compared to LEDs fabricated on sapphire. We discuss how these LED devices could be manufactured using a roll‐to‐roll process and cost reductions that result from this. Large‐area LED sheets can then be used to monolithically integrate MicroLEDs into paper‐thin and flexible displays. [ABSTRACT FROM AUTHOR]

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High-power quantum cascade lasers (QCLs) have a wide application prospect. In this paper, a high-power high-beam-quality device with a large ridge width is demonstrated. The effect of different ridge widths on mode loss was studied, and the results showed that the mode loss decreased as the ridge width increased. Furthermore, as the width of the ridge increased, the temperature of the active region rose. In the experiment, the wafers were grown by metal–organic chemical vapor deposition (MOCVD), and the ridge width of the device was controlled by wet etching. A laser with a ridge width of 15 µm and a length of 5 mm achieved an output of 2.2 W under 288 K continuous wave (CW) operation, with a maximum slow-axis divergence angle of 27.2° and a device wavelength of 5 μm. The research results of this article promote the industrial production of base transverse mode QCL. [ABSTRACT FROM AUTHOR]

Based on metal organic chemical vapor deposition (MOCVD), growth mechanism and stress modulation of van der Waals (vdW) heteroepitaxial GaN microwave material were studied with few-layer BN as an interlayer on 4-inch sapphire substrates. The influence of AlN nucleate process on growth mechanism of GaN buffer layer and its correlation with crystalline quality, stress, and electrical properties were discussed. A stress modulation scheme based on AlN/ AlGaN composite nucleation process is proposed, achieving stress well in control for large-size vdW heteroepitaxy firstly. The as-grown GaN microwave material possesses a wafer bow of + 20. 4 μm, fullwidth at half maximum of GaN (002) / (102) peaks of 471. 6/933. 5 arcsec, root-mean-square roughness of 0. 52 nm and electron mobility of 2 000 cm² / (V·s). Finally, largesize wafe-scale GaN microwave material was successfully separated from sapphire substrate by a mechanical lift-off process, providing convenience for transfering to high thermal conductivity substrates and creating conditions for fabricating high-power RF devices. [ABSTRACT FROM AUTHOR]

Quantum well infrared photodetectors (QWIPs) have been demonstrated to be a suitable candidate for IR detection applications. These detectors attracted increasing interest due to their design flexibility and broad spectral absorption from short wave (SWIR) to long wave infrared (LWIR) and high uniformity. In this paper, we demonstrate device design, growth, and characterization of a p-type AlxGa1-xN/GaN quantum well infrared photodetector (QWIP) for near IR absorption with 1.55 μm peak grown by metal organic chemical vapor deposition (MOCVD). Utilizing a p-QWIP allows for normal incidence light absorption due to the strong band mixing between heavy and light holes at k ≠ 0 which eliminates the need for light couplers such as grating and facilitates the fabrication of large focal plane arrays (FPAs). We developed MOCVD growth conditions to achieve nm-thick and smooth interfaces in QWIP. Sample characterizations including atomic force microscopy (AFM) show uniform surface morphology with RMS roughness ∼0.5 nm. Scanning transmission electron microscopy (STEM) was used to characterize layer thicknesses and interface roughness. We demonstrate energy band diagram simulation of an AlxGa1-xN/GaN p-QWIP by considering polarization chargers to determine the accurate band offset and adjust the absorption wavelength (ISBT energies). Our results show the feasibility of MOCVD-grown p-type AlxGa1-xN/GaN QWIP for IR absorption and open a pathway for further research and growth development on III-Nitride p-QWIPs, allowing growth and fabrication of large focal plane arrays.

Beta-phase gallium oxide (β-Ga2O3) is a cutting-edge ultrawide bandgap (UWBG) semiconductor, featuring a bandgap energy of around 4.8 eV and a highly critical electric field strength of about 8 MV/cm. These properties make it highly suitable for next-generation power electronics and deep ultraviolet optoelectronics. Key advantages of β-Ga2O3 include the availability of large-size single-crystal bulk native substrates produced from melt and the precise control of n-type doping during both bulk growth and thin-film epitaxy. A comprehensive understanding of the fundamental growth processes, control parameters, and underlying mechanisms is essential to enable scalable manufacturing of high-performance epitaxial structures. This review highlights recent advancements in the epitaxial growth of β-Ga2O3 through various techniques, including Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Mist Chemical Vapor Deposition (Mist CVD), Pulsed Laser Deposition (PLD), and Low-Pressure Chemical Vapor Deposition (LPCVD). This review concentrates on the progress of Ga2O3 growth in achieving high growth rates, low defect densities, excellent crystalline quality, and high carrier mobilities through different approaches. It aims to advance the development of device-grade epitaxial Ga2O3 thin films and serves as a crucial resource for researchers and engineers focused on UWBG semiconductors and the future of power electronics.

Germanium diselenide (GeSe2) is a 2D semiconductor with air stability, a wide bandgap, and anisotropic optical properties. The absorption and photoluminescence (PL) of single‐crystalline 2D GeSe2 grown by metal‐organic chemical vapor deposition and their dependence on temperature and polarization are studied. The PL spectra exhibit peaks at 2.5 eV (peak A) and 1.8 eV (peak B); peak A displays a strongly polarized emission along the short axis of the crystal, and peak B displays a weak polarization perpendicular to that of peak A. With increasing temperature, peak B shows anomalous behaviors, i.e., an increasing PL energy and intensity. The excitation energy‐dependent PL, time‐resolved PL, and density functional theory calculations suggest that peak A corresponds to the band‐edge transition, whereas peak B originates from the inter‐band mid‐gap states caused by selenium vacancies passivated by oxygen atoms. The comprehensive study on the PL of single‐crystalline GeSe2 sheds light on the origins of light emission in terms of the band structure of anisotropic GeSe2, making it beneficial for the corresponding optoelectronic applications. [ABSTRACT FROM AUTHOR]

The lattice parameter and thermal expansion coefficient mismatch between the silicon substrate and GaN lead to high tensile stress, which makes the GaN epitaxial layer prone to cracking. Effective compensation of tensile stress on GaN to prevent cracking is an important issue in GaN epitaxial growth. In this work, GaN‐on‐silicon materials with different AlGaN buffer layer structures are prepared by metal‐organic chemical vapor deposition (MOCVD). The GaN epitaxial material with a smooth and crack‐free surface is fabricated by inserting 7 AlGaN buffer layers. The crystal quality of GaN is characterized using high resolution X‐ray diffraction (HRXRD). The full‐width half maximum (FWHM) value of GaN(002) and GaN(102) crystal plane is 398 and 780 arcsec, respectively. The surface root mean square (RMS) roughness of GaN material is 0.31 nm, and the vertical breakdown voltage (BV) of the epitaxial wafer reaches 918 V. The results show that high Al content of the AlGaN buffer layer can effectively reduce the tensile stress and dislocation density of the GaN layer when the entire AlGaN layer thickness remains constant. Suppressing the generation of surface cracks and improving the crystal quality can improve the vertical breakdown voltage and two‐dimensional electron gas (2‐DEG) characteristics of GaN epitaxial wafers. [ABSTRACT FROM AUTHOR]

Germanium diselenide (GeSe2) is a 2D semiconductor with air stability, a wide bandgap, and anisotropic optical properties. The absorption and photoluminescence (PL) of single‐crystalline 2D GeSe2 grown by metal‐organic chemical vapor deposition and their dependence on temperature and polarization are studied. The PL spectra exhibit peaks at 2.5 eV (peak A) and 1.8 eV (peak B); peak A displays a strongly polarized emission along the short axis of the crystal, and peak B displays a weak polarization perpendicular to that of peak A. With increasing temperature, peak B shows anomalous behaviors, i.e., an increasing PL energy and intensity. The excitation energy‐dependent PL, time‐resolved PL, and density functional theory calculations suggest that peak A corresponds to the band‐edge transition, whereas peak B originates from the inter‐band mid‐gap states caused by selenium vacancies passivated by oxygen atoms. The comprehensive study on the PL of single‐crystalline GeSe2 sheds light on the origins of light emission in terms of the band structure of anisotropic GeSe2, making it beneficial for the corresponding optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this work, we investigated the MOCVD conditions to synthesize thin films with the hexagonal P63cm h-LuMnO3 phase as a potential low-band gap ferroelectric material. The main parameters investigated were the ratio of organometallic starting materials, substrate temperature, and annealing effect. Two different substrates were used in the study: fused silica (SiO2) glass and platinized silicon (Pt\Ti\SiO2\Si(100)). In order to investigate the thermodynamic stability and quality of the developed phases, a detailed analysis of the crystal structure, microstructure, morphology, and roughness of the films was performed by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Raman spectroscopy, and piezoelectric force microscopy (PFM). Molar compositions in the film within 0.93 < |Lu|/|Mn| < 1.33 were found to be suitable for obtaining a single-phase h-LuMnO3. The best films were obtained by depositions at 700 °C, followed by thermal treatments at 800 °C for long periods of up to 12 h. These films exhibited a highly crystalline hexagonal single phase with a relatively narrow direct band gap, around 1.5 eV, which is within the expected values for the h-LuMnO3 system. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have emerged as a promising class of materials with unique physical and chemical properties that offer exciting prospects for various applications. Among all the synthesis methods, chemical vapor deposition (CVD) techniques have demonstrated great advantages in the large-scale production of 2D materials with a controlled thickness. One of the main challenges in the growth of 2D materials is the need for high temperatures and crystalline substrates, which restrict the scalability and compatibility of 2D materials with existing manufacturing processes, due to the high thermal budget and the necessity to transfer the 2D films to secondary substrates. Low-temperature growth methods for 2D materials have the potential to overcome this challenge and enable the integration of 2D materials into a wide range of devices and applications. In recent years, there have been substantial efforts to develop low-temperature growth techniques for different 2D materials, including graphene, hexagonal boron nitride and transition metal dichalcogenides. These methods include thermal CVD, plasma-enhanced CVD, atomic layer deposition and metal-organic chemical vapor deposition. This review not only discusses the progress in the growth but also highlights the applications of low-temperature-grown 2D materials in various fields, such as field effect transistors, sensors, photodetectors, catalysts, batteries and supercapacitors. [ABSTRACT FROM AUTHOR]

A method for defects extraction for a mercury cadmium telluride (MCT) multilayer lowbandgap heterostructure is presented. The N+/T/p/T/P+/n+ epitaxial layer was deposited on a GaAs substrate by a metal-organic chemical vapour deposition (MOCVD). The absorber was optimized for a cut-off wavelength of λc= 6 µm at 230 K. Deep-level transient spectroscopy (DLTS) measurements were conducted for the isolated junctions of the N+/T/p/T/P+/n+ heterostructure. Three localised point defects were extracted within the ptype active layer. Two of them were identified as electron traps and one as a hole trap, respectively. [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]

The surface morphology of a buffer template is an important factor in the heteroepitaxial integration of optoelectronic devices with a significant lattice mismatch. In this work, InP-based long-wave infrared (~8 µm) emitting quantum cascade lasers with active region designs lattice-matched to InP were grown on GaAs and Si substrates employing InAlGaAs step-graded metamorphic buffer layers, as a means to assess the impact of surface roughness on device performance. A room-temperature pulsed-operation lasing with a relatively good device performance was obtained on a Si template, even with a large RMS roughness of 17.1 nm over 100 µm2. Such results demonstrate that intersubband-operating devices are highly tolerant to large RMS surface roughness, even in the presence of a high residual dislocation density. [ABSTRACT FROM AUTHOR]

High-temperature annealing has been regarded as an effective technology to improve the performance of Ga2O3-based solar-blind photodetectors (SBPDs). However, as a metastable phase, ε-Ga2O3 thin film may undergo phase transformation during post-annealing. Therefore, it is necessary to investigate the effect of the phase transition and the defect formation or desorption on the performance of photodetectors during post-annealing. In this work, the ε-Ga2O3 thin films were grown on c-plane sapphire with a two-step method, carried out in a metal-organic chemical vapor deposition (MOCVD) system, and the ε-Ga2O3 metal-semiconductor-metal (MSM)-type SBPDs were fabricated. The effects of post-annealing on ε-Ga2O3 MSM SBPDs were investigated. As a metastable phase, ε-Ga2O3 thin film undergoes phase transition when the annealing temperature is higher than 700 °C. As result, the decreased crystal quality makes an SBPD with high dark current and long response time. In contrast, low-temperature annealing at 640 °C, which is the same as the growth temperature, reduces the oxygen-related defects, as confirmed by X-ray photoelectron spectroscopy (XPS) measurement, while the good crystal quality is maintained. The performance of the SBPD with the post-annealing temperature of 640 °C is overall improved greatly compared with the ones fabricated on the other films. It shows the low dark current of 0.069 pA at 10 V, a rejection ratio (Rpeak/R400) of 2.4 × 104 (Rpeak = 230 nm), a higher photo-to-dark current ratio (PDCR) of 3 × 105, and a better time-dependent photoresponse. These results indicate that, while maintaining no phase transition, post-annealing is an effective method to eliminate point defects such as oxygen vacancies in ε-Ga2O3 thin films and improve the performance of SBPDs. [ABSTRACT FROM AUTHOR]

Ultrathin Ge single‐junction (1J) solar cells transferred onto a flexible substrate are envisioned to open up a novel lattice‐matched thin‐film InGaP/(In)GaAs/Ge tandem solar cell for enabling highly efficient, low‐cost, and light‐weight flexible devices. The ultrathin Ge 1J solar cell structures are epitaxially grown onto a GaAs substrate via a low‐pressure metal–organic chemical vapor deposition system using an isobutylgermane metalorganic source as a Ge precursor. A simple and fast epitaxial lift‐off method allows the epi structures to transfer onto the flexible substrates, by which 2 inch wafer‐scale flexible ultrathin Ge 1J solar cells with the mechanical stability under bending test (R = 12.5 mm) are fabricated. Their maximum power conversion efficiency (5.40%) is achieved with the optimum thickness of Ge p‐n junction as well as a delta‐doping technique that utilizes the multiple cycles of Ga‐dopant injection and halt during the growth of thick p‐Ge base layer. The power‐to‐weight ratio value of the ultrathin Ge 1J solar cells is 56.65 times higher than that of bulk‐type Ge solar cells, holding great potential to be used for the power sources of unmanned aerial vehicles as well as the portable and wearable devices. [ABSTRACT FROM AUTHOR]

Acquiring homogeneous and reproducible wafer-scale transition metal dichalcogenide (TMDC) films is crucial for modern electronics. Metal–organic chemical vapor deposition (MOCVD) offers a promising approach for scalable production and large-area integration. However, during MOCVD synthesis, extraneous carbon incorporation due to organosulfur precursor pyrolysis is a persistent concern, and the role of unintentional carbon incorporation remains elusive. Here, we report the large-scale synthesis of molybdenum disulfide (MoS2) thin films, accompanied by the formation of amorphous carbon layers. Using Raman, photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM), we confirm how polycrystalline MoS2 combines with extraneous amorphous carbon layers. Furthermore, by fabricating field-effect transistors (FETs) using the carbon-incorporated MoS2 films, we find that traditional n-type MoS2 can transform into p-type semiconductors owing to the incorporation of carbon, a rare occurrence among TMDC materials. This unexpected behavior expands our understanding of TMDC properties and opens up new avenues for exploring novel device applications. [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]

Abstract Aluminum nitride (AlN) grown on vertical surfaces can be utilized for the fabrication of advanced piezoelectric microelectromechanical systems (MEMS). The in‐plane motion of the parts of a MEMS element is possible when AlN is deposited on the vertical surfaces of the moving structure. For the best device performance, AlN must have high crystal quality, uniform coverage of the vertical sidewalls, and c‐axis crystalline orientation perpendicular to the plane of a vertical surface. The impact of the surface roughness (Rq) of the vertical sidewalls formed in Si using wet and dry etching methods on the crystal quality, crystallographic orientation, and uniformity of the metalorganic chemical vapor deposited (MOCVD) AlN thin films is studied in this paper. In both cases, AlN films demonstrated full sidewall coverage and grew crystalline in the c‐axis direction. AlN films grown on vertical Si surfaces achieved using anisotropic wet etching are highly crystalline and oriented in [0001] direction, while the films grown on vertical surfaces achieved using dry etching displayed a lower level of alignment with the Si sidewalls.

Using four-dimensional scanning transmission electron microscopy, we demonstrate a method to visualize grains and grain boundaries in WSe2 grown by metal organic chemical vapor deposition (MOCVD) directly onto silicon dioxide. Despite the chemical purity and uniform thickness and texture of the MOCVD-grown WSe2, we observe a high density of small grains that corresponds with the overall selenium deficiency we measure through ion beam analysis. Moreover, reconstruction of grain information permits the creation of orientation maps that demonstrate the nucleation mechanism for new layers-triangular domains with the same orientation as the layer underneath induces a tensile strain increasing the lattice parameter at these sites.

Volatile, reactive, and thermally stable organometallic copper and silver complexes are of significant interest as precursors for the metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) of ultra-thin metallic films. Well-established CuI and AgI precursors are commonly stabilized by halogens, phosphorous, silicon, and oxygen, potentially leading to the incorporation of these elements as impurities in the thin films. These precursors are typically stabilized by a neutral and anionic ligand. Recent advancements were established by the stabilization of these complexes using N-heterocyclic carbenes (NHCs) as neutral ligands. To further enhance the reactivity, in this study the anionic ligand is sequentially changed from β-diketonates to β-ketoiminates and β-diketiminates, yielding two new CuI and two new AgI NHC-stabilized complexes in the general form of [M(NHC) (R)] (M = Cu, Ag; R = β-ketoiminate, β-diketiminate). The synthesized complexes were comparatively analyzed in solid, dissolved, and gaseous states. Furthermore, the thermal properties were investigated to assess their potential application in MOCVD or ALD. Among the newly synthesized complexes, the β-diketiminate-based [Cu(tBuNHC) (NacNacMe)] was identified to be the most suitable candidate as a precursor for Cu thin film deposition. The resulting halogen-, oxygen-, and silicon-free CuI and AgI precursors for MOCVD and ALD applications are established for the first time and set a new baseline for coinage metal precursors.

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]

Metal-Organic CVD method (MOCVD) allows for deposition of ultrathin 2D transition metal dichalcogenides (TMD) films of electronic quality onto wafer-scale substrates. In this work, the effect of temperature on structure, chemical states, and electronic qualities of the MOCVD MoS2 films were investigated. The results demonstrate that the temperature increase in the range of 650 °C to 950 °C results in non-monotonic average crystallite size variation. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectroscopy investigation has established the film crystal structure improvement with temperature increase in this range. At the same time, X-Ray photoelectron spectroscopy (XPS) method allowed to reveal non-stoichiometric phase fraction increase, corresponding to increased sulfur vacancies (VS) concentration from approximately 0.9 at.% to 3.6 at.%. Established dependency between the crystallite domains size and VS concentration suggests that these vacancies are form predominantly at the grain boundaries. The results suggest that an increased Vs concentration and enhanced charge carriers scattering at the grains' boundaries should be the primary reasons of films' resistivity increase from 4 kΩ·cm to 39 kΩ·cm. [ABSTRACT FROM AUTHOR]

Among semiconductor metal oxides, that are an important class of sensing materials, titanium dioxide (TiO2) thin films are widely employed as sensors because of their high chemical and mechanical stability in harsh environments, non-toxicity, eco-compatibility, and photocatalytic properties. TiO2-based chemical oxygen demand (COD) sensors exploit the photocatalytic properties of TiO2 in inducing the oxidation of organic compounds to CO2. In this work, we discuss nanostructured TiO2 thin films grown via low-pressure metal organic chemical vapor deposition (MOCVD) on metallic AISI 316 mesh. To increase the surface sensing area, different inorganic acid-based chemical etching protocols have been developed, determining the optimal experimental conditions for adequate substrate roughness. Both chemically etched pristine meshes and the MOCVD-coated ones have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) microanalysis, and X-ray photoelectron spectroscopy (XPS). We demonstrate that etching by HCl/H2SO4 at 55 °C provides the most suitable surface morphology. To investigate the behavior of the developed high surface area TiO2 thin films as COD sensors, photocatalytic degradation of functional model pollutants based on ISO 10678:2010 has been tested, showing for the best performing acid-etched mesh coated with polycrystalline TiO2 an increase of 60% in activity, and degrading 66 µmol of MB per square meter per hour. [ABSTRACT FROM AUTHOR]

Zirconia layers are often used as thermal barriers. In recent years, depositions by chemical vapor deposition methods using a metalorganic precursor (MOCVD) have been primarily investigated. Here, we combine MOCVD with plasma activation ‐ plasma‐enhanced chemical vapor deposition (PECVD]) ‐ of the gas phase and/or the growth surface to lower the growth temperature and to allow for a flexible coating design. PECVD causes the precursor to be transformed into a chemically active species, yielding thin films with a five times higher sticking coefficient compared to MOCVD. This leads to the onset of crystallization at lower surface temperatures. Carbon is incorporated at oxygen sites, so that the crystalline structure of zirconia is preserved, but the electrical conductivity is affected. The thermal conductivity is like that of pure zirconia. [ABSTRACT FROM AUTHOR]

In this article, a high-composition (>35%) thick-barrier (>30 nm) AlGaN/AlN/GaN high-electron-mobility transistor (HEMT) structure grown on a sapphire substrate with ultra-low sheet resistivity (<250 Ω/□) is reported. The optimization of growth conditions, such as reduced deposition rate, and the thickness optimization of different epitaxial layers allowed us to deposit a crack-free high-composition and thick AlGaN barrier layer HEMT structure. A significantly high two-dimensional electron gas (2DEG) density of 1.46 × 1013 cm−2 with a room-temperature mobility of 1710 cm2/V·s was obtained via Hall measurement using the Van der Pauw method. These state-of-the-art results show great potential for high-power Ga-polar HEMT design on sapphire substrates. [ABSTRACT FROM AUTHOR]

We employed the selective-area-epitaxy technique using metalorganic chemical vapor deposition to fabricate and study samples of semiconductor heterostructures that incorporate highly strained InGaAs quantum wells (980–990 nm emission wavelength). Selective area epitaxy of InGaAs quantum wells was performed on templates that had a patterned periodic structure consisting of a window (where epitaxial growth occurred) and a passive mask (where epitaxial growth was suppressed), each with a width of 100 µm for every element. Additionally, a selectively grown potential barrier layer was included, which was characterized by an almost parabolic curvature profile of the surface. We conducted a study on the influence of the curvature profile of the growth surface on the optical properties of InGaAs quantum wells and the spatial distribution of composition in an ultrawide window. Our results showed that, under fixed selective-area-epitaxy conditions, the composition of the InxGa1−xAs and the wavelength of the quantum-well emission changed across the width of the window. Our study demonstrates that increasing the curvature profile of the growth surface of highly strained quantum wells leads to a transition in the photoluminescence wavelength distribution profile across the window, from quasi-parabolic to inverted parabolic. [ABSTRACT FROM AUTHOR]