Metalorganic Vapor Deposition Research Articles

Improvement of electrical properties by insertion of AlGaN interlayer for N-polar AlGaN/AlN structures on sapphire substrates

In this study, we propose nitrogen-polar (N-polar) Al0.1Ga0.9N/Al0.9Ga0.1N/aluminum nitride (AlN) structures. N-polar Al0.1Ga0.9N/Al0.9Ga0.1N/AlN was grown on a sapphire substrate with a misorientation of 2° with respect to the m-axis using metal–organic vapor deposition. The effects of varying the Al0.9Ga0.1N interlayer thickness from 30 nm to 1 μm using pulsed H2 etching on the planarity and current–voltage characteristics of the samples were investigated. The current first improved upon increasing the interlayer thickness from 30 to 300 nm, owing to the reduction in interfacial impurities between (aluminum) gallium nitride (Al)GaN) and Al0.9Ga0.1N, but subsequently decreased upon further increasing the thickness because of the relaxation growth of the interlayer. Furthermore, pulsed H2 etching of the Al0.9Ga0.1N interlayer suppressed step bunching and improved planarity. Subsequently, the proposed method was employed to fabricate N-polar Al0.1Ga0.9N/Al0.9Ga0.1N/AlN heterostructure FETs, which demonstrated five times higher source-drain current (I DS) than that of conventional structures without an interlayer.

(Invited) Dilute Anion Alloyed III-Nitride Nanowires for Photoelectrochemical Water Splitting

The record efficiencies in photovoltaic devices and hydrogen production via photoelectrochemical water splitting have been achieved in both cases by employing complex architectures of III-V alloys 1, which has been enabled by the outstanding charge carrier transport properties, band gap and band edge engineering flexibility, as well as highly mismatch growth that can be achieved in III-V alloys by controlling their chemical composition.It has been extensively demonstrated that Molecular Beam Epitaxy (MBE) and Metal-Organic Physical Vapor Deposition (MOPVD) techniques can produce III-V multinary alloys with compositions beyond miscibility gaps due to their “far from equilibrium” nature. And although great progress has been made towards improving the growth rate in these techniques, III-V device synthesis cost is still significantly higher (one order of magnitude) than Si solar cells manufacturing technologies 2. In this context, it is necessary to develop novel synthesis methods that yield high crystalline quality III-V alloys, higher throughput, and lower operational cost. For instance, Hydride/Halide Vapor Phase Epitaxy HVPE-grown GaAs top cell incorporated in a GaAs/Si tandem cell is an example of an optimized photovoltaic device with 31.4% efficiency, showcasing the uttermost potential of this growth method 2.More recently, Halide Vapor Phase Epitaxy growth of GaSbzP1-z polycrystalline free-standing films with up to 6.7% antimony incorporation and growth rates around 500 µm/h has been reported3. Linear sweep voltammetry measurements in 1M H2SO4 using GaSbzP1-z photoanodes showed lower onset potentials and higher fill factors compared to single crystal GaP. These results have been attributed to the visible light absorbing capabilities (direct band gaps between 2.2 and 2.5 eV), and lower charge transfer resistance at the semiconductor/electrolyte interface.On the other hand, a novel method for gallium nitridation involving plasma-activated nitrogen species dissolution into molten gallium has enabled the growth of single crystal GaN4. Furthermore, dilute anion Ga-Nitride alloys have been synthesized with the same technique but including other V-group species ions, i.e., Sb+ and Bi+, that can substitute nitrogen forming ternary GaSbxN1-x and GaBiyN1-y.In this presentation, we show the progress with dilute anion alloyed III-Nitride nanowires, GaSbxN1-x and GaBiyN1-y, synthesized by dissolving gallium, antimony or bismuth and plasma-activated nitrogen species into copper or gold droplets. Antimony and bismuth incorporation levels determined through x-ray diffraction c-plane peak shift, x and y, reached levels as high as 5.6 and 8.8 at%, respectively, resulting in direct band gap energies around 2.0 eV, determined through diffuse reflectance and photocurrent spectroscopy measurements. The visible light absorbing nanowire films exhibited photocurrent onset potentials around 0.0 V vs RHE when tested in 1 M sulfuric acid solution and 3-electrode setup with Ag/AgCl reference and Pt counter electrodes. 2-electrode chronoamperometry measurements with p-Si and n-type dilute alloys showed stable photocurrent densities up to 8.5 mA*cm-2 in 30 h. These results show the promising potential of dilute anion alloyed III-Nitrides as stable photoanodes for water splitting applications, and demonstrate the advantage of this novel synthesis technique over MOCVD that in previous studies has enabled the obtention of 0-D or 1-D GaSbxN1-x structures with up to 7% anion incorporation, while compromising crystalline quality.5

Toluene combustion over Co3O4-CNTs/PSSF catalysts and investigation of the effects of acid treatment on catalytic activity

BackgroundCo3O4 shows potential as a cost-effective alternative to precious metal catalysts for VOCs catalytic combustion. However, its catalytic activity requires further enhancement. MethodsA new type of paper-like carbon nanotube membrane composite (CNTs/PSSF) was used as a support to prepare Co3O4-CNTs/PSSF catalysts by metal-organic vapor deposition (MOCVD) and impregnation method (IM) respectively for toluene combustion. Besides, the effects of acid treatment to support on the catalytic activity were investigated. Various characterization techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and oxygen temperature-programmed desorption (O2-TPD), were employed to evaluate the effects of different preparation methods and acid treatment on the structure and catalytic performance mechanism of Co3O4-CNTs/PSSF. Significant findingsThe preparation method significantly affects the catalyst's properties and catalytic activity. Compared with IM, the MOCVD-prepared catalysts show stronger coordination of carbon nanotubes, resulting in more oxygen vacancies and surface active oxygen. Additionally, oxygenous groups introduced by HNO3 form Co-O-C linkage between Co and CNTs, promoting oxygen vacancies and enhancing surface active oxygen content, thereby dramatically improving the catalyst's catalytic activity, especially for HIM-10 whose T90 is reduced by 140 °C. This work provides insights for enhancing the catalytic combustion activity of cobalt oxide.

X-Rays Diffraction Study of InGaN/GaN Heterostructures Grown by MOCVD Technique at Different Temperatures

Indium gallium nitride / gallium nitride (InGaN/GaN) heterostructures were grown by using metal organic vapor deposition technique with four different growth temperatures (740 °C, 760 °C, 780 °C, and 800 °C). The structural properties and crystalline quality were investigated using high resolution X-ray diffraction (HRXRD) technique. XRD ω-2θ scan mode at GaN (002) diffraction plane was performed to assess the film’s quality. Through the simulation fitting, the indium composition and the thickness of the thin films were obtained. From the observation, an increase in the growth temperature resulted in higher intensity and smaller full-width at half maximum value of the InGaN (002) diffraction peak, which indicated improvement to the crystalline quality of the InGaN/GaN heterostructure. Moreover, the indium composition of the InGaN epilayer was found to decrease with an increase of the growth temperature due to the thermal decomposition of In-N bond and its re-evaporation from the growing surfaces.

The dependence of indium incorporation on specified temperatures in growing InGaN/GaN heterostructure using MOCVD technique

In this study, InGaN/GaN heterostructures were grown using metal organic vapor deposition (MOCVD) at different temperatures (800°C, 750°C and 700°C). The structural, crystallinity, surface morphology and optical properties were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and ultraviolet-visible (UV-Vis) spectrophotometer, respectively. From observation, it is found that the indium composition was obtained from XRD through the process of fitting of the simulation. The process of indium incorporation is found to be sensitive to temperature variances. When the temperature is further reduced, the indium incorporation process would become stagnant as the decomposition process of ammonia would be less efficient. FE-SEM images have revealed surface-related defects such as V-pits. The secondary energy gap is obtained from the optical characterization which confirmed the incorporation of indium in the epilayers.

Analysis of Transferred MoS2 Layers Grown by MOCVD: Evidence of Mo Vacancy Related Defect Formation

A low-temperature multi-frequency electron spin resonance (ESR) study has been carried out on 1, 3.5, and 6 layer thick MoS2 films, grown by metal organic vapor deposition (MOCVD) and subsequently transferred on SiO2/Si. This reveals the observation of a previously unreported, nearly isotropic signal at g ≈ 1.9998 with corresponding spin center (spin S = ½) densities ranging from ∼6 × 108 cm−2 to ∼5 × 1011 cm−2. The ESR investigation is closely combined with an in-depth analysis by an assortment of other experimental techniques, including atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), to ultimately result in the assignment of the ESR signal to a defect of intrinsic nature, most likely a Mo vacancy (VMo) related defect located at MoS2 grain edges or boundaries. The oxidation of the 2D material at grain edges and boundaries combined with the applied water-based transfer procedure is demonstrated to play a crucial role in the generation of the newly observed defect, thus advising caution with the currently applied process method. The presented analysis, which combines a variety of experimental techniques, contributes to the fine-tuning of the CVD growth and transfer process of high-quality few-layer MoS2 intended for next-generation nanoelectronic devices.

Study on Optical Properties and Waveguide Structure Optimization of Semiconductor Lasers with InGaAs Quantum Well

InGaAs quantum wells (QWs) are grown on GaAs substrates by metal-organic chemieal vapor deposition (MOCVD). Sample grown on substrates (100) oriented 2° off towards <111> exhibits relatively high photoluminescence (PL) intensity and narrow full-width at half-maximum (FWHM). Increasing growth rate leads to the enhancement of PL intensity and decrease of FWHM. Asymmetric waveguide layers are applied to reduce the confinement factor of base mode and increase the loss of higher-order mode.

Orientations of Al4C3 and Al films grown on GaAs substrates

A method for growth of aluminum epilayers on III-V substrates using metalorganic chemic vapor deposition (MOCVD) processes could be beneficial for optoelectronic and photovoltaic device fabrication. However, deposition from common precursors under standard MOCVD conditions results in polycrystalline Al4C3. Both Al4C3 films grown on GaAs (100) substrates, and those grown on GaAs (111) B substrates, show strong alignment of the rhombohedral [110] for the Al4C3 crystallites with the in-plane GaAs <110> directions. However, by using plasma-enhanced MOCVD at low growth temperatures, elemental Al can be deposited. Al growth by this method on (001), (111) B and (110) GaAs substrates gave textured, polycrystalline films. In all cases, the Al crystallites are primarily oriented with a <110> aligned with an in-plane <110> of the substrate at initial growth stages. These insights may lead towards growth of large-grained or epitaxial Al films.

Highly sensitive two-dimensional MoS2 gas sensor decorated with Pt nanoparticles.

A two-dimensional molybdenum disulfide (MoS2)-based gas sensor was decorated with Pt nanoparticles (NPs) for high sensitivity and low limit of detection (LOD) for specific gases (NH3 and H2S). The two-dimensional MoS2 film was grown at 400°C using metal organic gas vapour deposition. To fabricate the MoS2 gas sensor, an interdigitated Au/Ti electrode was deposited using the electron beam (e-beam) evaporation method with a stencil mask. The MoS2 gas sensor without metal decoration sensitively detects NH3 and H2S gas down to 2.5 and 30 ppm, respectively, at room temperature (RT). However, for improved detection of NH3 and H2S gas, we investigated the functionalization strategy using metal decoration. Pt NP decoration modulated the electronic properties of MoS2, significantly improving the sensitivity of NH3 and H2S gas by 5.58× and 4.25×, respectively, compared with the undecorated MoS2 gas sensor under concentrations of 70 ppm. Furthermore, the Pt NP-decorated MoS2 sensor had lower LODs for NH3 and H2S gas of 130 ppb and 5 ppm, respectively, at RT.

Buried-Heterostructure Quantum Cascade Lasers Fabricated Using a Sacrificial Layer and a Two-Step Regrowth Process

We report various aspects related to the selective area growth of thick InP:Fe layers by metal organic vapor deposition and their application to buried-heterostructures. In particular, we focus on the development of planar buried-heterostructure-quantum cascade lasers using selective wet chemical etching for ridge mesa preparation and versatile regrowth processes. After describing the optimization of the insulating properties of InP:Fe layers, we expose our approach to circumvent the difficulties inherent to the selective area growth on non-planar structures. By adding an InGaAs/InP layer stack (where, the InGaAs layer is used as a sacrificial layer) on the top of the active region, reproducible regrowths have been successfully carried out with good optical, electrical and crystalline quality. Using this method, buried-heterostructure quantum cascade lasers characterized in TM00 mode, exhibited output powers in the range of 2.5 W and wall plug efficiencies of about 13% at room temperature.

Control of Wigner localization and electron cavity effects in near-field emission spectra of In(Ga)P/GaInP quantum-dot structures

Structural and emission properties of few-electron In(Ga)P/GaInP quantum dots (QDs) representing natural Wigner molecules (WM) and whispering gallery mode (WGM) electron ($e$) cavities have been investigated. QD structures were grown using self-organized metal-organic vapor phase epitaxy and deposition from $\ensuremath{\sim}3$ to 7 monolayers of InP at $700{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Using atomic force microscopy, transmission electron microscopy, near-field scanning optical microscopy (NSOM), and $\ensuremath{\mu}$-photoluminescence ($\ensuremath{\mu}$-PL) spectra we obtained In(Ga)P/GaInP QDs having lateral size 80--180 nm, height 5--30 nm, Ga content 0.0--0.4, density $2\ensuremath{-}10\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}2}$, and electron population up to 20 and demonstrated control of their density and size distribution. Using high-spatial-resolution low-temperature PL spectra, NSOM imaging, and calculations of charge density distributions we observed Wigner localization and $e$-cavity effects for a series of dots having quantum confinement $\ensuremath{\hbar}{\ensuremath{\omega}}_{0}=0.5\ensuremath{-}6\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$. We used these data together with time-resolved PL measurements to clarify the effect of Coulomb interaction and WM formation on emission spectra of few-electron QDs. We present direct observation of $2e$, $6e$, and $9e$ WMs; $2e$ and $4e$ WGMs; and Fabry-Perot $e$ modes and establish conditions of $e$-WGM-cavity formation in these QDs.

Crystal Size and Stress Account in Reciprocal Space Map

In this study, five periodic InGaN / GaN LED (light emitting diode) structures grown by the Metal Organic Vapor Deposition (MOCVD) at different active layer growth temperatures were studied. These structures were grown as InGaN / GaN multiple quantum wells (MQW) between c-oriented sapphire substrate and n-GaN and p-AlGaN + GaN contacts. These constructions were characterized by the high-resolution X-ray diffraction (HR-XRD) system. HRXRD patterns obtained by X-ray diffraction and Reciprocal space maps were performed from the same data. One of the most effective ways of studying the crystal lattice is reciprocal space mapping with HR-XRD technique. This technique does not damage the sample. Information can be obtained from the internal system of the sample or from the intermediate layer including substrate. Using the FWHM (β hkl ) values and the elastic coefficients of the structures obtained for each of the three samples separately with the inverse mesh technique, D (nm) particle size, σ (GPa) uniform stress, e strain, u (kJm -3 ) anisotropic energy density parameters were calculated. These calculations were done in a Scherrer method and Uniform Deformation Model (UDM) which is the Williamson Hall method, modified uniform Williamson stresses model (USDM) and Uniform Deformation Energy Density Model (UDEDM). The results show that the stretching in the crystal size is very little. Line expansion in HR-XRD is due to small crystal size and lattice strain. UDEDM, one of the W-H methods, has emerged as the most suitable model for stretching..

Electrodeposition and Photocharacterization of In2Se3 Thin Films Using PP-ALD for Use As a Potential Photoanode

Indium (III) selenide is an n-type semiconductor that displays 4 main crystal structures. While the more prevalent α and β structures have a direct bandgap of 1.62 eV, the γ structure has been found to have a bandgap of 1.9 eV.1,2 In current work, In2Se3 films were deposited using a pulse potential atomic layer deposition (PP-ALD) technique derived from E-ALD that relies upon the principles of ALD and underpotential deposition (UPD) to create ordered atomic layers. In PP-ALD both precursors, In and Se, are present in one solution that is pumped through the flow cell introducing the ions to the substrate. A cathodic pulse is then used to reductively deposit limited amounts of In and Se on the substrate surface, followed by an anodic pulse used to oxidatively strip any bulk In away from the surface leaving atomic layers of In2Se3. At pH=1, the deposition process creates bubbles in the flow cell that lead to regions of limited deposition. However, at pH=2, less bubbles are formed during the deposition process, leading to more uniform samples. Further investigations into the optimal cathodic and anodic deposition potentials for the PP-ALD program at pH=2 need to be done. These In2Se3 films have been demonstrated to have good photocurrent and have potential as an n-type photoanode in photoelectrochemical cell applications. Czerniawski, J.; Stickney, J.; Electrodeposition of In2Se3 Using Potential Pulse Atomic Layer Deposition. J. Phys. Chem. C 2016. 120, 16162-16167.Chang, K.; Lahn, S.; Chang, J. Growth of single-phase In2Se3 by using metal organic vapor deposition with dual-source precursors. Appl. Phys. Lett. 2006. 89, 182118.

INVESTIGATION OF ZnO NANO STRUCTURES FABRICATED ON AL2O3 SUBSTRACTES BY MOCVD

High quality ZnO nanostructures were grown directly on sapphire subtracts by metal organic vapor deposition. By changing the growth conditions, the different nano structures (nanorods,nanotubes, nanowalls, nanonetworks) can be selectively. These nanostructures were all epitaxially grown and had the same epitaxial relationship with respect to the substrate. Mechanisms corresponding to different nanostructures were discussed. The nanostructures exhibited stable excitonic states at room temperature, and the emission due to exciton-exciton scattering was observed

Thermal resistance measurement of In3SbTe2 nanowires

The thermal resistance along the thickness of In3SbTe2 crystalline nanowires was measured using the scanning thermal microscopy in 3ω mode. The nanowires were grown by metal organic vapor deposition, exploiting the VLS mechanism induced by Au metal‐catalyst nanoparticles and harvested on a SiO2/Si substrate. Two nanowires with different thickness (13 and 23 nm) were investigated. The thermal resistance of the nanowires was determined using two different approaches; the first one exploits the experimental data, whereas the second one is more sophisticated, since it involves a minimization procedure. Both methods led to comparable values of the thermal resistance along the transverse direction (thickness) of the nanowire. The obtained results were explained starting from the mean free path of phonons calculated in the In3SbTe2 bulk.

Highly elongated vertical GaN nanorod arrays on Si substrates with an AlN seed layer by pulsed-mode metal–organic vapor deposition

Precisely controlled morphology of GaN nanorods was obtained on a thin AlN seed layer and their height increased as the diameter of the mask openings decreased.

Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process

Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga0.97N0.9O0.09 is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga0.97N0.9O0.09 of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86w/w% of gallium and Indium are leached using 4M HCl, 100°C and pulp density of 100kg/m3, respectively. After mechanochemical oxidation, both these processes achieved 90w/w% of gallium and 1.86w/w% of indium leaching at their optimum condition.

Thermoelectric Properties of ZnO Thin Films Grown by Metal-Organic Chemical Vapor Deposition

ABSTRACTThermoelectric (TE) materials have gained renewed interests in last decades for both power generation and energy conservation from waste-heat harvesting. Research in the discovery of best TE materials such as, bulk materials, complex structures, and low dimensional play crucial role to achieve high efficiency TE materials. Wide bandgap materials like ZnO can be promising candidate for high efficiency TE power generation owing to its low-cost, nontoxicity, and stability at high temperatures. In this paper, room temperature TE properties of thin film ZnO grown by metal organic vapor deposition (MOCVD) are reported. TE properties of thin film GaN are also studied as reference to that of thin film ZnO. Moreover, high resolution x-ray diffraction (HRXRD), room temperature photoluminescence (PL) with deep ultraviolet (DUV) spectroscopy (excitation at 248nm), hall effect, and thermal gradient methods have been employed to investigate the effect of structural, optical, electrical, and thermal properties of the samples, respectively. The effect of doping concentrations and structural defects on Seebeck coefficients of thin film ZnO are systematically studied and discussed in this work.

Extraordinary N atom tunneling in formation of InN shell layer on GaN nanorod m-plane sidewall

We report the extraordinary tunneling process that finds the lower cohesive energy route for stablizing InN shell layer on m-plane sidewall of GaN nanorod. The [0001] orientated GaN nanorod array is grown on sapphire substrate patterned with Ga nanoparticle by metal–organic vapor deposition method, based on which the simulation structures of c-plane top surface and m-plane sidewall surface is constructed for the first-principles calculations. The results show that the introduction of In wetting monolayer could effectively lower the cohesive energy of adalayers on non-polar GaN surfaces. Most importantly, it is revealed that there exists an extraordinary tunneling process in which the N atoms will drag out the In wetting atoms and tunnel through to form stable InN shell layer on the nanorod sidewall.

Large interface diffusion in endotaxial growth of MnP films on GaP substrates

The metal organic vapor deposition of MnP films on GaP (100) substrates is shown to have a substantial endotaxial component. A study of the growth time evolution of the endotaxial depths of MnP grains reveals a diffusion-controlled growth with a relatively large diffusion coefficient of Mn in GaP. The value (2.2 ± 1.5) × 10−15 (cm2/s) obtained at 650 °C is at least two orders of magnitude larger than the reported Mn diffusion in bulk GaP. GaP surface mounds provide further indirect evidence that this large diffusion coefficient is concurrent with the out-diffusion of Ga atoms at the growing MnP/GaP interface. No trace of dislocations could be observed at or near this interface, which strongly suggests that Mn diffusion occurs through vacant sites generated by the difference between the crystallographic structures of MnP and GaP.