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A series of (In 1- x Al x) 2 O 3 (0.1 ≤ x ≤ 0.6) films with tunable bandgap were grown on MgO (100) substrates by MOCVD. The influences of chemical compositions and growth temperatures on the film properties were studied systematically. XRD analyses indicated that the film quality degraded from crystalline to amorphous structure as Al concentration (x) increased. The (In 1- x Al x) 2 O 3 films prepared at 700 °C exhibited better film crystallinity than those of the ones grown at 600 °C. The films prepared at 700 °C with x = 0.1–0.3 showed an epitaxial In 2 O 3 <111> orientation with the corresponding growth relationship of In 2 O 3 (111)∥MgO (100). The film with x = 0.2 exhibited the best crystallinity and the largest grain size of 25.9 nm. The Hall mobilities and resistivities of the films were influenced evidently by Al concentrations. The Hall mobility showed a monotonous decrease from 12 to 1.1 cm2V−1s−1 as x increased from 0.1 to 0.6. The lowest resistivity of 9.2 × 10−3 Ω cm was acquired for the film with x = 0.2. The average transmittances in the visible region for all the films were beyond 83%. The bandgap of the (In 1- x Al x) 2 O 3 films can be regulated in the range of 3.85–4.88 eV by changing Al concentrations from 0.1 to 0.6. [ABSTRACT FROM AUTHOR]

In this work, a solar-blind ultraviolet (UV) photodetector based on a three-terminal enhancement-mode (E-mode) Si-doped β -Ga2O3 (β -Ga2O3:Si) metal-semiconductor field-effect transistor structure is demonstrated, whose threshold voltage (V th) and subthreshold swing are 4.04 V and 1.4 V decâˆ'1, respectively. A 400 nm thick β -Ga2O3:Si thin film is prepared on sapphire substrate by using metal-organic chemical vapor deposition method. Controlling the channel currents by the Schottky gate voltage in the dark and under illuminations, the photodetector shows dark current (I dark) as low as 13.4 pA, photo-to-dark current ratio of 4.85 Ă— 104 and linear dynamic range of 29.6 dB, illuminated by 254 nm UV light of 245 ÎĽ W cmâˆ'2. As the UV light is turned on and off, the output current rise and decay time (Ď„ r and Ď„ d) are 420 ms and 350 ms. Moreover, at drain voltage (V ds) of 5 V and gate voltage (V gs) of 0 V, the responsivity (R), specific detectivity (D*) and external quantum efficiency are achieved as 74 A Wâˆ'1, 2.15 Ă— 1014 cm Hz1/2 Wâˆ'1 (Jones) and 3.6 Ă— 104%, respectively. [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]

The structurally related cobalt β‐diketonate complexes Co(acac)2, Co(acac)2 ⋅ TMEDA, Co(tfac)2 ⋅ TMEDA, and Co(hfac)2 ⋅ TMEDA (acac=2,4‐pentanedionate, tfac=1,1,1‐trifluoro‐2,4‐pentane‐dionate, hfac=1,1,1,5,5,5‐hexafluoro‐2,4‐pentane‐dionate, TMEDA=N,N,N′,N′‐tetramethylethylenediamine) were thermochemically (thermogravimetric analysis, differential scanning calorimetry) and spectroscopically (infrared, UV‐VIS and electron resonance spectroscopy) characterised and used as precursor for the MOCVD growth of cobalt monoxide (CoO) thin films. The influence of the degree of fluorination of the cobalt precursors on the morphology (scanning electron microscopy) and phase composition (X‐ray diffraction) of the CoO films is demonstrated. Carbon, nitrogen and fluorine impurities as a result of the thermal decomposition of the 2,4‐pentanedionate and tetraamine ligands in the films were identified by X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry, Rutherford backscattering spectrometry and nuclear reaction analysis. In addition, the influence of these contaminants on the electrocatalytically activity for the oxygen evolution reaction (OER) in alkaline media of the MOCVD grown CoO films is shown. [ABSTRACT FROM AUTHOR]

In this work, multi-finger current aperture vertical electron transistors (CAVETs) are fabricated with co-integrated high electron mobility transistors (HEMTs). The devices are realized by Mg-ion implantation and metalorganic chemical vapor deposition (MOCVD) regrowth. The intrinsic CAVET design is optimized for robust device performance and applied on multi-finger devices having a total gate periphery of ${W}_{{\text {G}}} =13.5$ mm and ${W}_{{\text {G}}} =77$ mm. Mappings of the transfer characteristics revealed reliable turn-off behavior demonstrating the suitability of the intrinsic device layout. The largest CAVETs revealed a total ON-state resistance of ${R}_{ \mathrm{\scriptscriptstyle ON}} = 1.67\,\,\Omega $ and a maximum drain current of ${I}_{{\text {D},\text {MAX}}} =20.3$ A at ${V}_{\text {GS}} = {3}$ V. A pulse robustness of ${P}_{\text {PULS}} =976$ W at ${V}_{\text {DS}} =50$ V and a pulsewidth of 500 $\mu \text{s}$ is shown without thermal destruction. Additionally, HEMTs are co-integrated on-chip. This combination of HEMTs and reliable large area CAVETs enables the design of high-performance, monolithically integrated GaN power circuits (GaN power ICs) based on the CAVET technology. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD), which involves chemical reactions in gases for deposition on a heated surface, is an extensively used manufacturing technique for obtaining thin films of materials like silicon, graphene, silicon carbide, aluminum nitride, and gallium nitride (GaN). The process is driven by heat and mass transfer, fluid flow, and chemical reactions in the gases and at the surface. GaN is one of the most promising materials for manufacturing optical and electronic devices. However, the reliability and durability of the GaN-based devices depend on the crystalline quality of the thin films used. In this study, the epitaxial growth of GaN thin films on sapphire (Al2O3) wafers is carried out in a vertical rotating disk metalorganic chemical vapor deposition (MOCVD) system. Epitaxial growth refers to the process of growing a crystal of a particular orientation on the top of another crystal, with the orientation being determined by the underlying crystal. MOCVD reactors are CVD systems that use metalorganic compounds that consist of metal and organic ligands, leading to materials like GaAs, AlN, InN, and GaN. The quality of the thin films is largely determined by the choice of operating conditions such as the flowrate, surface temperature, and concentration of the metalorganic precursors that decompose due to heat in the reactor, react, and deposit the desired material on the surface of a wafer or a heated susceptor. In this experimental study, the crystalline quality and surface morphology of GaN thin films are evaluated using atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy. The correlation between the crystalline quality of GaN thin films and the flowrate of the precursors is examined in detail on the basis of an evaluation of the dislocation density. The results indicate that a low concentration (V/III) ratio, where V and III refer to elements in the fifth and third groups of the periodic table, is beneficial for obtaining a high deposition rate since a low value of this ratio implies a high precursor concentration. However, it negatively affects the crystalline quality of the thin film. Similarly, high V/III ratios lead to low deposition rates and better crystalline quality, indicating the need to optimize the process. [ABSTRACT FROM AUTHOR]

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

Copper dithiocarbamate and aluminium dithiocarbamate were prepared and then characterized by infrared spectroscopy. The combination of the prepared precursors in different ratios was deposited on glass substrates using metal-organic chemical vapour deposition (MOCVD) technique at 450oC through the pyrolysis of the precursors to yield Cu-Al-S thin films. Compositional, morphological, structural and optical characterizations were then carried out. The compositional analysis revealed that the ratio of Cu to Al in the precursor is not preserved in the films. Morphological study showed that the films are polycrystalline in nature whose homogeneity and grain size distribution decrease with a decrease in Al content of the films. The crystallinity of the films was further revealed from the PXRD results with the formation of the Cu-Al-S crystal structure as the Al content increases in the precursor. The energy gap obtained falls between 2.63 and 2.75 eV which decreases as the Al content in the films decreases. Optical constants such as refractive index and extinction coefficient exhibit a decreasing trend as the Al content in the film decreases.

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the (2¯01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices.

In this study, the surface morphology and luminescence characteristics of InGaN/GaN multiple quantum wells were studied by applying different flow rates of ammonia during MOCVD growth, and the best growth conditions of InGaN layers for green laser diodes were explored. Different emission peak characteristics were observed in temperature-dependent photoluminescence (TDPL) examination, which showed significant structural changes in InGaN layers and in the appearance of composite structures of InGaN/GaN quantum wells and quantum-dot-like centers. It was shown that these changes are caused by several effects induced by ammonia, including both the promotion of indium corporation and corrosion from hydrogen caused by the decomposition of ammonia, as well as the decrease in the surface energy of InGaN dot-like centers. We carried out detailed research to determine ammonia’s mechanism of action during InGaN layer growth.

Abstract We report optical phonon vibration modes in ensembles of self-catalyzed InP/InAs/InP multi core-shell one-dimensional nanostructures (nanopillars and nanocones) grown on InP(111)B substrates using liquid indium droplets as a catalyst via metal-organic chemical vapor deposition. We characterized the Raman vibration modes of InAs E1(TO), InAs A1(TO), InAs E1(LO), InP E1(TO), InP A1(LO), and InP E1(LO) from the ensemble of as-grown nanostructures. We also identified second-order Raman vibration modes, associated with InP E1(2TO), E1(LO+TO), and E1(2LO), in the InP/InAs/InP core-shell nanopillars and nanocones. Raman spectra of InP/InAs/InP nanopillars showed redshift and broadening of LO modes at low-frequency branches of InAs and InP. Due to the polar nature in groups III–V nanowires, we observed strong frequency splitting between InAs E1(TO) and InAs A1(LO) in InP/InAs/InP nanocones. The Raman resonance intensities of InP and InAs LO modes are found to be changed linearly with an excitation power. By tilting the substrate relative to the incoming laser beam, we observed strong suppression of low-frequency branch of InP and InAs LO phonon vibrations from InP/InAs/InP nanocones. The integrated intensity ratio of InP E1(TO)/E1(LO) for both nanostructures is almost constant at 0-degree tilt, but the ratio of the nanocones is dramatically increased at 30-degree tilt. Our results suggest that Raman spectroscopy characterization with a simple substrate tilting method can provide new insights into non-destructive characterization of the shape, structure, and composition of the as-grown nanostructures for the wafer-scale growth and integration processing of groups III–V semiconducting hetero-nanostructures into nanoelectronics and photonics applications.

Abstract AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) suffer from electron overflow and insufficient hole injection. In this paper, novel DUV LED structures with superlattice electron deceleration layer (SEDL) is proposed to decelerate the electrons injected to the active region and improve radiative recombination. The effects of several chirped SEDLs on the performance of DUV LEDs have been studied experimentally and numerically. The DUV LEDs have been grown by metal-organic chemical vapor deposition (MOCVD) and fabricated into 762 × 762 μm2 chips, exhibiting single peak emission at 275 nm. The external quantum efficiency of 3.43% and operating voltage of 6.4 V are measured at a forward current of 40 mA, indicating that the wall-plug efficiency is 2.41% of the DUV LEDs with ascending Al-content chirped SEDL. The mechanism responsible for this improvement is investigated by theoretical simulations. The lifetime of the DUV LED with ascending Al-content chirped SEDL is measured to be over 10,000 h at L50, due to the carrier injection promotion.

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 WSe 2 using four-dimensional scanning transmission electron microscopy (4D-STEM). Experimentally, WSe 2 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 WSe 2 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.

In this paper, we reported changes in the growth morphology of n+InAs nanowires (NWs) doped with Te which were selectively grown on nano-hole patterned InP(111)B substrates using an MOCVD method. While the vertical growth of InAs NWs in the direction was extremely suppressed, their lateral growth was enhanced when the diethyl-tellurium (DETe) flow rate was increased as they grew. Moreover, the sidewall planes evolved from (11¯0) (90° against the (111) plane) to a reverse-tapered morphology, which had a 62° slope against the InP (111)B plane, when the Te flow rate and growth time were increased. This indicates that the surfactant effect of adsorbed Te atoms on InAs changes the relative growth rate between (111) and (11¯0) due to the increase in surface free energy in the growth plane.

In this article, we reported on a Ga2O3-based Schottky barrier diode and heterojunction diode from MOCVD. The Si-doped n-type Ga2O3 drift layer, grown by MOCVD, exhibited high crystal quality, flat surfaces, and uniform doping. The distribution of unintentional impurities in the films was studied. Then nickel Schottky barrier diode and p-NiO/n-Ga2O3 heterojunction diode were fabricated and measured. Without any electric field management structure, the Schottky barrier diode and heterojunction diode have specific resistances of 3.0 mΩ·cm2 and 6.2 mΩ·cm2, breakdown voltages of 380 V and 740 V, thus yielding power figures of merit of 48 MW·cm−2 and 88 MW·cm−2, respectively. Besides, both devices exhibit a current on/off ratio of more than 1010. This shows the prospect of MOCVD in power device manufacture.

β-Ga2O3 thin films grown on widely available c-plane sapphire substrates typically exhibit structural defects due to significant lattice and thermal expansion mismatch, which hinder the use of such films in electronic devices. In this work, we studied the impact of a nucleation layer on MOCVD-grown β-Ga2O3 thin film structure and morphology on a c-plane sapphire substrate. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, transmission and scanning electron microscopy, while the composition was confirmed by X-ray photoelectron spectroscopy and micro-Raman spectroscopy. It was observed that the use of a nucleation layer significantly increases the grain size in the films in comparison to the films without, particularly in the samples in which H2O was used alongside O2 as the oxygen source for the nucleation layer growth. Our study demonstrates that a nucleation layer can play a critical role in obtaining high quality β-Ga2O3 thin films on c-plane sapphire.

The ultra-wide bandgap (~6.2 eV), thermal stability and radiation tolerance of AlN make it an ideal choice for preparation of high-performance far-ultraviolet photodetectors (FUV PDs). However, the challenge of epitaxial crack-free AlN single-crystalline films (SCFs) on GaN templates with low defect density has limited its practical applications in vertical devices. Here, a novel preparation strategy of high-quality AlN films was proposed via the metal organic chemical vapor deposition (MOCVD) technique. Cross-sectional transmission electron microscopy (TEM) studies clearly indicate that sharp, crack-free AlN films in single-crystal configurations were achieved. We also constructed a p-graphene/i-AlN/n-GaN photovoltaic FUV PD with excellent spectral selectivity for the FUV/UV-C rejection ratio of >103, a sharp cutoff edge at 206 nm and a high responsivity of 25 mA/W. This work provides an important reference for device design of AlN materials for high-performance FUV PDs.

This paper reports an AlGaN-based ultraviolet-B light-emitting diode (UVB-LED) with a peak wavelength at 293 nm that was almost free of efficiency droop in the temperature range from 298 to 358 K. Its maximum external quantum efficiencies (EQEs), which were measured at a current density of 88.6 A cm–2, when operated at 298, 318, and 338 K were 2.93, 2.84, and 2.76%, respectively; notably, however, the current droop (J-droop) in each of these cases was less than 1%. When the temperature was 358 K, the maximum EQE of 2.61% occurred at a current density of 63.3 A cm–2, and the J-droop was 1.52%. We believe that the main mechanism responsible for overcoming the J-droop was the uniform distribution of the concentrations of injected electrons and holes within the multiple quantum wells. Through the subtle design of the p-type AlGaN layer, with the optimization of the composition and doping level, the hole injection efficiency was enhanced, and the Auger recombination mechanism was inhibited in an experimental setting.

The mechanical stability of commercial GaP/Si templates during thermal annealing and subsequent growth of GaP and AlGaP using metal-organic chemical-vapour deposition is investigated. Although the as-grown GaP layer of the template originally presents an excellent surface morphology, annealing at temperatures between 645 ∘ C to 845 ∘ C to remove the native oxide prior to growth leads to plastic relaxation, accompanied by a variety of defects, including a dense grid of micro-twins. These micro-twins detrimentally affect GaP and AlGaP layers grown subsequently on the template. [ABSTRACT FROM AUTHOR]

Using the example of epitaxial lateral overgrowth of AlN on trench‐patterned AlN/sapphire templates, the impact of introducing a high‐temperature annealing step into the process chain is investigated. Covering the open surfaces of sapphire trench sidewalls with a thin layer of AlN is found to be necessary to preserve the trench shape during annealing. Both the influence of annealing temperature and annealing duration are investigated. To avoid the deformation of the AlN/sapphire interface during annealing, the annealing duration or annealing temperature must be low enough. Annealing for 1 h at 1730 °C is found to allow for the lowest threading dislocation density of 3.5 × 108 cm−2 in the subsequently grown AlN, while maintaining an uncracked smooth surface over the entire 2 in. wafer. Transmission electron microscopy study confirms the defect reduction by high‐temperature annealing and reveals an additional strain relaxation mechanism by accumulation of horizontal dislocation lines at the interface between annealed and nonannealed AlN. By applying a second annealing step, the dislocation density can be further reduced to 2.5 × 108 cm−2. [ABSTRACT FROM AUTHOR]

Red LEDs were grown by metalorganic chemical vapor deposition with a high active region temperature of 870 °C on a relaxed InGaN/GaN superlattice buffer. The buffer was 100% biaxially relaxed by the thermal decomposition of an InGaN underlayer, measured by high resolution X-ray diffraction. Fabricated LEDs showed a low forward voltage of 2.25 V at a current density of 25 Acmâˆ'2 with no Al-containing layers in the active region, a peak emission wavelength of 633 nm at 200 Acmâˆ'2 and an on-wafer peak external quantum efficiency of 0.05%. Uniform red emission and relaxation were observed across a two inch substrate. [ABSTRACT FROM AUTHOR]

This paper details 3 years of cadmium telluride (CdTe) photovoltaic performance onboard the AlSat‐1N CubeSat in low earth orbit. These are the first CdTe solar cells to yield I–V measurements from space and help to strengthen the argument for further development of this technology for space application. The data have been collected over some 17 000 orbits by the CubeSat with the cells showing no signs of delamination, no deterioration in short circuit current or series resistance. The latter indicating that the aluminium‐doped zinc oxide transparent front electrode performance remained stable over the duration. Effects of temperature on open circuit voltage (Voc) were observed with a calculated temperature coefficient for Voc of −0.19%/°C. Light soaking effects were also observed to increase the Voc. The fill factor decreased over the duration of the mission with a major contribution being a decrease in shunt resistance of all four of the cells. The decrease in shunt resistance is speculated to result from gold diffusion from the rear contacts into the absorber and through to the front interface. This has likely resulted in the formation of a deep trap state within the CdTe and micro shunts formed between the rear and front contact. Further development of this technology should therefore utilise more stable back contacting methodologies more commonly employed for terrestrial CdTe modules. [ABSTRACT FROM AUTHOR]

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A new principle for supplying volatile precursors to MOCVD gas-phase chemical deposition systems is proposed, based on a two-stage evaporation of an organic solution of precursors from a soaked cotton thread, which passes sequentially through the zones of evaporation of the solvent and precursors. The technological capabilities of TSF-MOCVD (Thread-Solution Feed MOCVD) are demonstrated based on examples of obtaining thin epitaxial films of СеО2, h-LuFeO3 and thin-film heterostructures β-Fe2O3/h-LuFeO3. The results of studying the obtained films by X-ray diffraction, energy dispersive X-ray analysis, and high- and low-resolution transmission microscopy are presented. Using the TSF module, one can finely vary the crystallisation conditions, obtaining coatings of the required degree of crystallinity, as evidenced by the obtained dependences of the integral width of the h-LuFeO3 reflection on the film growth rate. Based on the TEM and XRD data, it was concluded that β-Fe2O3 grows epitaxially over the h-LuFeO3 layer. Thus, using TSF-MOCVD, one can flexibly change the composition of layered heterostructures and obtain highly crystalline epitaxial films with a clear interface in a continuous deposition process

The spectral response properties of AlGaN Schottky barrier detectors with different Al content were investigated. It was found that the responsivity of AlGaN detectors decreases with increase in Al content in AlGaN. It was found that neither dislocation density nor the concentration of carbon and oxygen impurities made any remarkable difference in these AlGaN devices. However, the positron annihilation experiments showed that the concentration of Al or Ga vacancy defects (more likely Ga vacancy defects) in AlGaN active layers increased with the increase in Al content. It is assumed that the Al or Ga vacancy defects play a negative role in a detector’s performance, which increases the recombination of photogenerated carriers and reduces the detector responsivity. It is necessary to control the concentration of vacancy defects for the high performance AlGaN detectors.

Very few sodium complexes are available as precursors for the syntheses of sodium-based nanostructured materials. Herein, the diglyme, triglyme, and tetraglyme (CH3O(CH2CH2O)nCH3, n = 2–4) adducts of sodium hexafluoroacetylacetonate were synthesized in a single-step reaction and characterized by IR spectroscopy, 1H, and 13C NMR. Single-crystal X-ray diffraction studies provide evidence of the formation of the ionic oligomeric structure [Na4(hfa)6]2−•2[Na(diglyme2]+ when the diglyme is coordinated, while a mononuclear seven-coordinated complex Na(hfa)•tetraglyme is formed with the tetraglyme. Reaction with the monoglyme (CH3OCH2CH2OCH3) does not occur, and the unadducted polymeric structure [Na(hfa)]n forms, while the triglyme gives rise to a liquid adduct, Na(hfa)•triglyme•H2O. Thermal analysis data reveal great potentialities for their applications as precursors in metalorganic chemical vapor deposition (MOCVD) and sol-gel processes. As a proof-of-concept, the Na(hfa)•tetraglyme adduct was successfully applied to both the low-pressure MOCVD and the sol-gel/spin-coating synthesis of NaF films.

The relationship between the purge time and the overall growth rate in pulsed injection metal–organic chemical vapor deposition with different V/III ratios is studied by numerical analysis. The transport behavior of TMAl and TMAlNH3 during the process is studied to understand the effect of the adductive reaction. The results show that, as the V/III ratio increases, there is a significant reduction in the average growth rate per cycle, without the addition of a purging H2 pulse between the III and V pulses, due to stronger adductive reaction. The adductive reaction can be reduced by inserting a purging pulse of pure H2 between the III and V pulses, but there is a decrease in the overall growth rate due to the longer cycle time. At smaller V/III ratios, the growth rate decreases with increasing purge times, since the gain in reducing the adductive reaction is offset by the detrimental effect of extending the cycle time. The degree of reduction in the adductive reaction is higher for larger V/III ratios. When the benefit of reducing the adductive reaction overcomes the deficiency of the extending cycle time, a remarkable enhancement of the growth rate can be obtained at high V/III ratios by inserting a pure H2 purge pulse between the III and V pulses. A higher overall growth rate can be achieved at higher V/III ratios by choosing an appropriate purge time.

Semipolar (112¯2) InGaN/GaN superlattice templates with different periodical InGaN layer thicknesses were grown on m-plane sapphire substrates using metal-organic chemical vapor deposition (MOCVD). The strain in the superlattice layers, the relaxation mechanism and the influence of the strain relaxation on the semipolar superlattice template were explored. The results demonstrated that the strain in the (112¯2) InGaN/GaN superlattice templates was anisotropic and increased with increasing InGaN thickness. The strain relaxation in the InGaN/GaN superlattice templates was related to the formation of one-dimension misfit dislocation arrays in the superlattice structure, which caused tilts in the superlattice layer. Whereas, the rate of increase of the strain became slower with increasing InGaN thickness and new misfit dislocations emerged, which damaged the quality of the superlattice relaxed templates. The strain relaxation in the superlattice structure improved the surface microtopography and increased the incorporation of indium in the InGaN epitaxial layers.

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]

The large‐area synthesis of high‐quality MoS2 plays an important role in realizing industrial applications of optoelectronics, nanoelectronics, and flexible devices. However, current techniques for chemical vapor deposition (CVD)‐grown MoS2 require a high synthetic temperature and a transfer process, which limits its utilization in device fabrications. Here, the direct synthesis of high‐quality monolayer MoS2 with the domain size up to 120 µm by metal‐organic CVD (MOCVD) at a temperature of 320 °C is reported. Owing to the low‐substrate temperature, the MOCVD‐grown MoS2 exhibits low impurity doping and nearly unstrained properties on the growth substrate, demonstrating enhanced electronic performance with high electron mobility of 68.3 cm2 V−1 s−1 at room temperature. In addition, by tuning the precursor ratio, a better understanding of the MoS2 growth process via a geometric model of the MoS2 flake shape, is developed, which can provide further guidance for the synthesis of 2D materials. [ABSTRACT FROM AUTHOR]

Advanced metal organic chemical vapor deposition technique (A-MOCVD) was used to grow 4-5 μm thick REBa2Cu3O7−δ (REBCO, RE = rare earth) films, doped with 5% and 15% Hf. Thick REBCO films doped with 5% Hf exhibit self-field critical current density (Jc) over 1.8 MA/cm2 at 77 K and 3 MA/cm2 at 65 K, 1.5 T. Increasing the Hf content to 15% resulted in Jc above 9 MA/cm2 at 20 K, 9 T. The effect of (Ba+Hf)/Cu content in Hf-added (5 and 15 mol.%) REBCO films on the critical current density at 77 K, 0 T, c-axis lattice parameter and out-of- plane texture has been studied. In addition to growth of thick film REBCO tapes with superior performance, the A-MOCVD reactor has been used to quadruple the precursor-to-film conversion efficiency above 45%. This achievement has a first order impact in lowering the cost of REBCO tapes made by A-MOCVD. [ABSTRACT FROM AUTHOR]

We have reported the development of an Advanced Metal-Organic Chemical Vapor Deposition (A-MOCVD) method featuring ohmic heating of the substrate for REBCO film growth, direct tape temperature monitoring, and laminar precursor flow. This A-MOCVD method has been used to fabricate 4–5  μm thick film REBCO tapes with record-high performance: critical currents exceeding 8700 A/12 mm at 30 K, 3 T; and engineering current density of 5200 A/mm2 at 4.2 K, 15 T. Recently, we constructed a pilot-scale reel-to-reel A-MOCVD system to scale up the technology to long tapes. Preliminary batches of tapes exhibit consistent performance and good uniformity along the length. An in-line 2D X-ray Diffraction (XRD) system has been integrated into the pilot A-MOCVD tool to monitor the REBCO texture and composition, RE2 O3 content, and the dimensions of BaMO3 (BMO, M=Zr,Hf) nanorods that act as artificial pinning centers. Specifically, the streaking angle between REBCO (103) and BZO (101) has been found to correlate well with (Ba+M)/Cu of the film, lift factor in critical current over a range of temperatures and magnetic fields, and the size of the BMO nanorods. The in-line 2D-XRD is expected to serve as a valuable quality measuring tool supporting realtime feedback control for the process to yield uniform and consistent manufacturing of high-performance REBCO tapes by Advanced MOCVD. [ABSTRACT FROM AUTHOR]

Metal-organic chemical vapor deposition (MOCVD) is a key technique for developing and manufacturing zinc oxide (ZnO) devices. The film quality and performance of these devices are influenced by the process parameters. In this study, the film deposition rate and film uniformity obtained from the simulations and experiments under different process parameters, such as the substrate temperature, operating pressure, mass fraction of the source gas, and inlet flow rate, are compared and verified. In addition, the corresponding temperature field, flow field, distribution of source mass fraction, and velocity field are analyzed using the computational fluid dynamics (CFD) method to explain the influence of the flow field change on deposition rate and film uniformity. This study also presents the correlation test for the film uniformity between the simulation and experimental results; it was found that all the 16 sets of results are significantly correlated and that more than half of them are highly correlated. To ensure the consistency of the experimental results and to prove their reliability, the repeatability test and stability test are conducted. [ABSTRACT FROM AUTHOR]

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In this article, a new data treatment based on time-resolved photoluminescence is presented. It works as a streak camera for infrared. A time-resolved photoluminescence spectrum for the HgCd0.33Te0.67 sample at 120 K was performed and analyzed. Typical time-resolved photoluminescence measurements, to compare our results with literature, were conducted. An interpretation of the behavior for three different time constants found in the signal is proposed. [ABSTRACT FROM AUTHOR]

Three InGaN/GaN quantum wells: S1 (830 °C), S2 (840 °C) and S3 (850 °C) with different barrier temperatures were grown by metal organic chemical vapor deposition (MOCVD). Due to the formation of high-density V-shaped pits, the perfect quantum well structure was destroyed and transformed into InGaN quantum dots (QDs)/quantum well (QW) hybrid structure. Atomic force microscopy (AFM), high-angle annular dark-field imaging (HAADF) and energy dispersive spectrometer (EDS) were employed to analyze the morphology and related causes of the three samples. The changes of quantum confined Stark effect (QCSE), nonradiative recombination center density and carrier localization effect at different barrier temperatures were analyzed by EPDD-PL (excitation power density dependent photoluminescence) and TD-PL (temperature dependent photoluminescence). The results show that QCSE is weaker at lower barrier temperature, because at lower temperature, the V-shaped pits are deeper, inducing more obvious stress release and lower the residual strain. With the increase of barrier growth temperature, the density of nonradiative recombination centers increase gradually. The internal quantum efficiency (IQE) of S1, S2 and S3 samples decrease with the increase of barrier growth temperature. Finally, it is found that the enhancement of QCSE and the higher density of nonradiative recombination centers are the main factors for the decrease of IQE with the increase of barrier growth temperature. [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]

We investigate the thin film quality of the epitaxial layer on Sn-doped (001)-oriented β -Ga 2 O 3 single crystal substrates. The homoepitaxial layer is grown by metal organic chemical vapor deposition (MOCVD) at 700 °C, 800 °C, 900 °C, and 1000 °C. To evaluate the grown epitaxial layer at different temperatures, the depletion layer of the Schottky barrier diode (SBD) is studied using the impedance-phase angle (Z-theta) via capacitance-voltage measurements. In addition, the Z-theta value is correlated with X-ray diffraction and transmission electron microscopy. The results show that the epitaxial layer grown at 900 °C has the best epitaxial layer quality. It is presumed that Z-theta measurements are a feasible and reliable approach to evaluate the epitaxial layer in Ga 2 O 3 -related devices. [ABSTRACT FROM AUTHOR]

A number of methods have been demonstrated to increase the sensitivity of fiber refractometers to changes in the surrounding media refractive index (SMRI). The sensor system is based on the effect of lossy mode resonance (LMR) in a thin multimode fiber with a thin film coating. A chemically resistant thin film of aluminum oxide (Al 2 O 3) was applied to the silica surface of an optical fiber by metalorganic chemical vapor deposition (MOCVD). For the first time, the possibility of obtaining aluminum oxide from a vapor-gas mixture of trimethylaluminium - isopropyl alcohol in a hydrogen reducing medium to reduce the carbon content in the sediment has been demonstrated. Using in situ control during the deposition of the coating, the movement of resonances in the transmission spectrum of the optical path was observed. The optical parameters of the deposited coating under various synthesis conditions in the temperature range from 470 to 550 °C were estimated by the movement, shape and depth of several orders of resonances. When creating test sensors, deposition was stopped when the resonance was in the spectral range of 400–1700 nm and their sensitivity in aqueous salt solutions (NaCl), as well as chemical resistance in acids (HCl, HNO 3 , H 2 SO 4 , H 3 PO 4) were evaluated. The maximum sensitivity of the implemented sensors for media with refractive indices of 1.34–1.37 was 2950 nm/RIU, which is one of the highest values found in the literature for sensors with Al 2 O 3 coating. The dependence between the temperature of the synthesis of coatings and the rate of their dissolution in orthophosphoric acid is demonstrated. It is shown that an increase in sensitivity of up to 30 % can be realized by changing the roughness of the surface of the coating or silica glass. [Display omitted] • Al 2 O 3 coatings for fiber refractometers were obtained using the MOCVD method. • Using lossy mode resonance, growth processes were studied in real time. • The influence of growth temperature on the chemical resistance of Al 2 O 3 is shown. • A method is described to increase the sensitivity of the sensor using H 3 PO 4. • The maximum sensitivity of the sensors for change refractive index was 2950 nm/RIU. [ABSTRACT FROM AUTHOR]

Traditional Au-catalyzed growth method of nanowires will mix Au atoms into Si substrates and InAs/GaSb axial heterojunction materials to introduce deep energy levels, which will seriously degrade the electrical and photoelectric properties of nanodevices. In this work, we studied in detail the effects of multiple growth parameters on self-catalyzed growth of InAs/GaSb axial heterostructured NWs on Si substrate by MOCVD. It is found that in the switching process from InAs material precursor to GaSb material precursor, if growth temperature of GaSb is not appropriate and switching time is too long, it will cause the decomposition and disappearance of InAs NWs, and directly terminate the realization of InAs/GaSb axial heterojunction NWs. Both the parameter windows of the growth temperature and V/III ratio are very narrow, which directly affects the growth trend of GaSb material in axial or radial deposition. It provides an important and meaningful method for self-catalyzed high-quality nanowires by MOCVD that up high pure GaSb nanowires requires the catalyzed guidance of alloy droplets and buffer seed nanowire and bottom InAs nanowires just meet both requirements. • We investigated influence of multiple growth parameters on self-catalyzed growth of heterostructured NWs. • GaSb NW can be grown with a high purity cubic zinc blende lattice structure. • By controlling Ga–In alloy droplets, axial or radial heterostructured NWs can be flexibly controlled. [ABSTRACT FROM AUTHOR]

Metal organic chemical vapour deposition (MOCVD) was used with a mixed single solid source precursors of copper dithiocarbamate (CuC10H16N2O2S4) and zinc dithiocarbamate (ZnC10H16N2O2S4) to prepare pyrolysed copper zinc sulphide thin films. The precursors were analysed by Fourier Transform Infrared Spectroscopy (FTIR), to determine the structures present. The films were deposited on glass substrates at a temperature of 420 0C. Experimental results showed that the compositional studies were found to be complementary. The structural analyses revealed that the film is crystalline with an average grain size of approximately 4 μm. An optical band gap energy of 2.50 eV was obtained with an absorbance that decreases with wavelength. The electrical characterization gave values of sheet resistance, resistivity and conductivity of the film as 5.13 x10-6 Ω/Sq, 2.27 x 10-1 Ω.cm and 3.61 x 10-2 (Ω.cm)-1 respectively. The findings confirmed that the synthesized precursors are potential materials for depositing high quality copper zinc sulphide thin films.

Controlling the morphology, orientation, and crystal phase of semiconductor nanowires is crucial for their future applications in nanodevices. In this work, zinc sulfide (ZnS) nanowires have been grown by metalorganic chemical vapor deposition (MOCVD), using gold or gold–gallium alloys as catalyst. At first, basic studies on MOCVD growth regimes (mass-transport, zinc- or sulfur- rich conditions) have been carried out for ZnS thin films. Subsequently, the growth of ZnS nanowires was investigated, as a function of key parameters such as substrate temperature, S/Zn ratio, physical state and composition of the catalyst droplet, and supersaturation. A detailed analysis of the structural properties by transmission electron microscopy (TEM) is given. Depending on the growth conditions, a variety of polytypes is observed: zinc-blende (3C), wurtzite (2H) as well as an uncommon 15R crystal phase. It is demonstrated that twinning superlattices, i.e., 3C structures with periodic twin defects, can be achieved by increasing the Ga concentration of the catalyst. These experimental results are discussed in the light of growth mechanisms reported for semiconductor nanowires. Hence, in this work, the control of ZnS nanowire structural properties appears as a case study for the better understanding of polytypism in semiconductor 1D nanostructures.