Pressure Metalorganic Chemical Vapor Deposition Research Articles

Improved surface morphology and reduced V-pits density of lattice-matched AlInN films grown by atmospheric pressure metalorganic chemical vapor deposition

AlInN has emerged as a promising material for advanced optoelectronic and electronic devices due to its unique properties. However, achieving AlInN layers with excellent surface morphology remains challenging. Here, Al0.83In0.17N layers lattice-matched to GaN/sapphire were grown by atmospheric-pressure metalorganic chemical vapor deposition at 875 °C. The lowest surface roughness measured by atomic force microscopy was 0.37 nm after optimizing the growth temperature and flux of precursors. The roughness value was constant in the range of 15–72 nm film thickness. Introducing a TMI pre-flow period before AlInN growth, further reduced roughness to 0.28 nm, although a graded inclusion of Ga into the AlInN near the GaN/AlInN interface was observed. This improved surface morphology was interpreted by the In-surfactant effect enriched by the pre-flow in the early stage of AlInN. Additionally, the V-pits density was as low as 2×105 cm−2, primarily due to high growth pressure and also influenced by relatively high growth temperature. Analysis of Al incorporation using second-order reaction model suggests that the severe parasitic reactions between TMA and NH3 at atmospheric pressure can be effectively eliminated by a high total gas flow rate of 72 slm, ensuring in-plane uniformity in surface morphology and relatively good crystalline quality.

The effect of Ag doping on the structure, optical, and electronic properties of ZnO nanostructures deposited by atmospheric pressure MOCVD on Ag/Si substrates

Atmospheric pressure metal–organic chemical vapour deposition was used to synthesize Ag-containing ZnO nanostructures of different morphology on Si substrates coated by Ag. Ag from Ag/Si substrates and Ag from silver acetylacetonate after its decomposition were used as a catalyst for ZnO nanocrystal growth for deposition of ZnO nanostructures with different morphologies. We investigated the relation of the structural parameters and chemical composition probed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy with the photoluminescence (PL) properties and electron–phonon coupling (EPC) reflected in the multi-phonon Raman spectra. The Raman and PL spectra were studied at different powers of the exciting laser radiation (P exc). The spectral position and width of the phonon Raman peaks and the near bandgap PL band at low P exc are supposed to be determined by the structural quality of the surfaces/boundaries of the crystallites. The intensity of the near-bandgap and defect-related PL and the magnitude of the EPC are additionally affected by the dopant concentration. Because of the large crystallite size (>30 nm, determined from XRD), the effects of phonon or electron confinement are negligible in these nanostructures. The behaviour of the position and width of phonon and PL bands with increasing P exc indicates that the heat dissipation in the film, which is dependent on the nanostructure morphology and Ag content, plays an important role. In addition, the cytotoxicity of ZnO:Ag nanostructures was investigated by using monolayer cell cultures of epithelioid origin Madin-Darby bovine kidney and Madin-Darby canine kidney cells at a MTT assay revealing that the level of silver doping of ZnO nanostructures, their morphology, and geometric dimensions determine their toxic effects.

The Effect of Ag-Doping on the Cytotoxicity of ZnO Nanostructures Grown on Ag/Si Substrates by APMOCVD

The search and development of new nanostructures and nanomaterials are very important for the progress of nanotechnology and modern microbiology. Due to the unique properties of silver and zinc oxide, these nanoparticles are the optimal basis for creating nanostructures with potential antiviral activity. An important issue in these studies is the establishment of cytotoxicity of these nanoparticles and their composites. Aim. To define the influence of substrate temperature and Ag concentration in ZnO lattice on the microstructure and cytotoxicity of zinc oxide nanostructures. Methods. Pure and Ag-doped ZnO nanostructures were grown on Ag/Si substrates by atmospheric pressure metalorganic chemical vapor deposition method using a mixture of zinc acetylacetonate and silver acetylacetonate powders as a precursor. Argentum thin films were deposited on Si substrates by a thermal evaporation method. MTT-assay was used for the analysis of MDBK and MDCK cell viability in the definition of zinc oxide nanostructure cytotoxicity. Results. Ag-doped zinc oxide nanostructures were grown and characterized by X-ray diff raction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. It was found that Si substrate and pure zinc oxide do not inhibit the cell viability of both epithelial cultures whereas Ag-doped ZnO nanostructures inhibit the cell viability because of all-time exposure in a sample without dilution. The cytotoxic effect was not observed at higher dilutions for Ag-doped zinc oxide nanostructures. Conclusions. The investigation of the effect of Ag-doping on the morphology and cytotoxicity of zinc oxide nanostructures is very important for implementing zinc oxide nanostructures into the current optoelectronics and photocatalysis.

The Influence of the Preheating Temperature of the (−2 0 1) β-Ga2O3 Substrates on c-Plane GaN Epitaxial Growth

In this paper, we demonstrate the direct epitaxial growth of c-plane GaN on a preheated (−2 0 1) β-Ga2O3 single-crystal substrate with no interlayer or pre-patterning processes by using the atmospheric pressure metalorganic chemical vapor deposition method. The results show that high-temperature preheating (>500 °C) can modify the surface morphology of the substrate so that the crystalline quality of the grown GaN layer can be improved. With higher preheated temperatures, the grown GaN layer reveals smaller FWHM (full width at half-maximum) of the X-ray rocking curve. In addition, we find that the photoluminescence spectra of the GaN layers reveal their narrowest linewidth at a preheated temperature of 800 °C. These results support improvements of crystalline quality and provide optimization of a c-GaN grown epitaxially on the preheated (−2 0 1) β-Ga2O3 substrates for further device fabrication.

Atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) growth of undoped and aluminium-doped ZnO thin film using hot wall reactor

In this contribution, a hot wall reactor via economic atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) was adopted for Un-doped and Al-doped Zinc oxide films were deposited on borosilicate glass and silicon substrates. To avoid the use of an expensive vacuum system, all experiments were realized at atmospheric pressure. The chemical reagents used for this experiment are Zinc acetylacetonate (Zn(acac)2) and aluminium acetylacetonates (Al (acac)2) under atmospheric conditions. The obtained films are characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Uv-–vis spectrometer, respectively. As results, it is found that The un-doped ZnO films are polycrystalline. However, a significant enhancement in the intensity of the relevant (100) reflection is observed when Zinc oxide films are doped with Al. It is also observed that the Al-doped Zinc oxide films present higher transparency in the visible region and resistivities of 2.55 ohm cm and 1.44 ohm cm for un-doped and Al doped films respectively

Improved Performance of Ge Solar Cell Using Graphene Quantum Dots.

We investigated the effect of graphene quantum dots (GQDs) on performance of single-junction Ge solar cell grown on (100) substrate by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Isobutylgermane (IBuGe) is used as a Ge precursor for the Ge solar cell growth. By employing GQDs, the power conversion efficiency of the Ge solar cell is improved up to 3.90% (Voc of 0.22 V, Jsc of 28.52 mA/cm², and FF of 63.83%) through effective photon management as compared to bare Ge solar cells of 3.24% under AM 1.5G illumination.

Application of ZnO Nanorods Based Whispering Gallery Mode Resonator in Optical Immunosensors

In this research a whispering gallery mode (WGM) resonator based on vertically oriented ZnO nanorods, which were formed on silicon surface (silicon/ZnO-NRs), has been applied in the design of optical immunosensor that was dedicated for the determination of grapevine virus A-type (GVA) proteins. Vertically oriented ZnO-NRs were grown on silicon substrates by atmospheric pressure metal organic chemical vapor deposition (APMOCVD) and the silicon/ZnO-NRs structures formed were characterized by structural and optical methods. Optical characterization demonstrates that silicon/ZnO-NRs-based structures can act as ‘whispering gallery mode’ (WGM) resonator where quasi-whispering gallery modes (quasi-WGMs) are generated. These quasi-WGMs were experimentally observed in the visible and infrared ranges of the photoluminescence spectra. In order to design an immuno-sensing system the anti-GVA antibodies were immobilized on the surface of silicon/ZnO-NRs and in this way silicon/ZnO-NRs/anti-GVA structure was formed. The immobilization of anti-GVA antibodies and then the interaction of silicon/ZnO-NRs/anti-GVA structure with GVA proteins (GVA-antigens) resulted in an opposite shifts of the WGMs peaks in the visible range of the photoluminescence spectra observed as a defect-related photoluminescence emission of ZnO-NRs. Here designed silicon/ZnO-NRs/anti-GVA immuno-sensing structure demonstrates the sensitivity towards GVA-antigens in the concentration range of 1-200 ng/ml. Bioanalytical applicability of the silicon/ZnO-NRs-based structures in the WGMs registration mode is discussed.

Fabricating GaN-based LEDs on (−2 0 1) β-Ga2O3 substrate via non-continuous/continuous growth between low-temperature undoped-GaN and high-temperature undoped-GaN in atmospheric pressure metal-organic chemical vapor deposition

This study demonstrates two approaches to the growth of GaN-based LEDs on (−2 0 1)-oriented β-Ga2O3 single crystal substrates using metal-organic CVD under atmospheric pressure. One approach induces non-continuous growth between low-temperature undoped-GaN (u-GaN) and high-temperature u-GaN, whereas the other approach induces continuous growth. We observed the following reduction in the FWHM of X-ray diffraction rocking curves: GaN (0 0 2) on (−2 0 1) β-Ga2O3 substrate (from 464 to 342 arcsec) and GaN (1 0 2) (from 886 to 493 arcsec). An LED with six pairs of InGaN/GaN multiple quantum wells was successfully fabricated on the (−2 0 1) β-Ga2O3 single crystal substrate.

Crystal Phase Control of ε-Ga2O3 Fabricated using by Metal-Organic Chemical Vapor Deposition

e-Ga2O3 thin films were grown on (0001) sapphire, (0001) GaN, and a low-temperature buffer layer at different temperatures and flow rates of bubbled H2O (oxygen source) using trimethylgallium and H2O as precursors by using atmospheric-pressure metal-organic chemical vapor deposition. Due to the atmospheric pressure conditions, most of the Ga2O3 thin films were not grown in a pure e-phase, but contain a small portion of the β-phase. The crystal structure, crystal quality, phase ratio, and surface morphology were analyzed by using X-ray diffraction, rocking curve measurements, and field-emission scanning electron microscopy. A certain minimum H2O flow rate was required to form e-Ga2O3 thin films, and the optimal growth temperature for e-Ga2O3 was 650°C. The β-phase fraction of the mixed-phase (e + β) thin films was dominant at temperatures higher than 650 °C. The crystallinities and phase compositions of the thin films changed with the flow rate of H2O. Nearly single-crystalline Ga2O3 thin films were successfully grown on GaN and sapphire, but not on a low-temperature buffer layer. Hexagonally shaped Ga2O3 islands become aligned in an ordered direction that correlated to the substrate’s orientation during the initial stage of the growth and coalesced to complete a two-dimensional layer as the growth went on.

Free standing c-GaN films grown by low-pressure metalorganic chemical vapor deposition on GaP (100) substrates

Gallium nitride (GaN) films were synthesized by low pressure metalorganic chemical vapor deposition on GaP (100) substrates. Samples were grown using three-step growth method, which includes a) a nitridation process of the GaP surface, b) the growth of a GaN buffer layer and c) the growth of the high-temperature epilayer. X-ray diffraction, Raman spectroscopy and FESEM and HRTEM were used to study the changes in the surface, which suggests that the cubic phase nucleation takes place during nitridation process and remained at the top surface, which results in preferential growth of c-GaN.

Surface morphological properties of CdxZn(1-x)S thin films deposited by low-cost atmospheric pressure metal organic chemical vapour deposition technique (AP-MOCVD)

The CdxZn(1-x)S films have been deposited by low cost atmospheric pressure metal organic chemical vapour deposition (AP-MOCVD) technique and the resulting morphological properties were successfully evaluated for solar cell applications. All morphological properties presented here were investigated by Field-Emission Scanning Microscopy (FESEM) and Energy Dispersive X-Ray (EDX) spectroscopy. It has been observed that the film thickness and grain size have been greatly influenced by the molar ratio of cadmium and zinc, deposition temperature and time. The average grain size of Cd0.5Zn0.5S films (98.16 nm thick) was obtained with deposition temperature and time of 440°C and 2.5 minutes, respectively.

A study on film formation mechanisms and precursor/solvent compatibility in PP-MOCVD of Al2O3 films using aluminum tri-sec-butoxide with hexane and toluene

Pulsed pressure metal-organic chemical vapor deposition (PP-MOCVD) has been used to deposit aluminum oxide films using aluminum tri-sec-butoxide (ASB) as a precursor and hexane and toluene as solvents at 475°C. Comparisons between solvent compatibility with ASB have been made. In addition to the solvents, different precursor/solvent solution concentrations (0.125mol% and 0.5mol%) and a shield have been used to investigate film formation mechanisms. This was done by studying the influence of these parameters on film properties (morphology and deposition rate). A droplet vaporization numerical model has been used to support explanations given for the dependence of properties on the process parameters. The results suggest that film formation might take place by four mechanisms including vapor phase deposition, Leidenfrost aerosol formation, homogeneous particle formation and liquid droplet impingement. The results also suggest that hexane has a better compatibility with ASB and is a better solvent than toluene.

Precursors for p‐Type Nickel Oxide: Atmospheric‐Pressure Metal–Organic Chemical‐Vapour Deposition (MOCVD) of Nickel Oxide Thin Films with High Work Functions

A series of unsymmetrical nickel β‐diketonate derivatives have been synthesised and structurally characterised for application as atmospheric‐pressure metal–organic chemical vapour deposition (AP‐MOCVD) precursors for nickel oxide. (TMEDA)Ni[MeC(O)CHC(O)OEt]2 (TMEDA = tetramethylethylenediamine) was selected and used to deposit NiO films of varying thickness onto commercial indium tin oxide (ITO)‐coated glass; the work function of the ITO was raised as a consequence.

Influence of Growth Temperature on the Characteristics of Single-Junction p–i–n InGaP Solar Cells.

Single-junction p–i–n InGaP solar cells are grown at various temperatures from 620 to 700 °C by low pressure metalorganic chemical vapor deposition on GaAs (001) substrates. The short circuit current density of the p–i–n InGaP solar cells increases by up to 38.8% when the growth temperature is reduced from 700 to 620 °C, while the open circuit voltage and fill factor show relatively small changes. The external quantum efficiency, especially, in the wavelength regime below 500 nm, is improved for the p–i–n InGaP solar cells grown at lower temperatures. The improvement might be attributed to the reduced absorption loss of the photons in the n-InGaP emitter region. The highest conversion efficiency of 11.01% is attributed from the p–i–n InGaP solar cell grown at 640 °C. Electron mobility and concentration of undoped InGaP layers are investigated as a function of the growth temperature and correlated with the p–i–n InGaP solar cell performance.

Highly efficient epitaxial Ge solar cells grown on GaAs (001) substrates by MOCVD using isobutylgermane

Single-junction Ge solar cells have been epitaxially grown on GaAs (001) substrates by a low pressure metalorganic chemical vapor deposition using isobutylgermane. Various growth conditions have been studied to reduce the high doping level of over 1×1019cm−3 of the p-type Ge epitaxial layer, which is detrimental to the minority carrier collection efficiency. By increasing the growth rate and employing a discontinuous doping technique, the p-type doping level of the epitaxial Ge layer has been lowered to 2×1018cm−3, and the hole mobility increased from 44 to 162cm2/Vs. A high power conversion efficiency of 6.72% can be achieved under AM1.5G illumination by the epitaxial Ge solar cell with the lowered doping level in the p-type Ge base region. The spectral response of the epitaxial Ge solar cell with a 5µm thick base layer is good enough to use for InGaP/GaAs/Ge triple-junction solar cells.

The Effect of Growth Temperature and V/III Flux Ratio of MOCVD Antimony Based Semiconductors on Growth Rate and Surface Morphology

Epitaxial Al x Ga 1-x Sb layers on GaSb and GaAs substrates have been grown by atmospheric pressure metalorganic chemical vapor deposition using TMAl, TMGa and TMSb. Nomarski microscope and a profiler were employed to examine the surface morphology and growth rate of the samples. We report the effect of growth temperature and V/III flux ratio on growth rate and surface morphology. Growth temperatures in the range of 520°C and 680°C and V/III ratios from 1 to 5 have been investigated. A growth rate activation energy of 0.73 eV was found. At low growth temperatures between 520 and 540°C, the surface morphology is poor due to antimonide precipitates associated with incomplete decomposition of the TMSb. For layers grown on GaAs at 580°C and 600°C with a V/III ratio of 3 a high quality surface morphology is typical, with a mirror-like surface and good composition control. It was found that a suitable growth temperature and V/III flux ratio was beneficial for producing good AlGaSb layers. Undoped AlGaSb grown at 580°C with a V/III flux ratio of 3 at the rate of 3.5 μm/hour shows p-type conductivity with smooth surface morphology

The relationship between the dislocations and microstructure in In0.82Ga0.18As/InP heterostructures.

In this work, we propose a formation mechanism to explain the relationship between the surface morphology (and microstructure) and dislocations in the In0.82Ga0.18As/InP heterostructure. The In0.82Ga0.18As epitaxial layers were grown on the InP (100) substrate at various temperatures (430 °C, 410 °C and 390 °C) using low pressure metalorganic chemical vapor deposition (LP-MOCVD). Obvious protrusions and depressions were obseved on the surface of the In0.82Ga0.18As/InP heterostructure because of the movement of dislocations from the core to the surface. The surface morphologies of the In0.82Ga0.18As/InP (100) system became uneven with increasing temperature, which was associated with the formation of dislocations. Such research investigating the dislocation of large lattice mismatch heterostructures may play an important role in the future-design of semiconductor films.

Correlation between mobility collapse and carbon impurities in Si-doped GaN grown by low pressure metalorganic chemical vapor deposition

In the low doping range below 1 × 1017 cm−3, carbon was identified as the main defect attributing to the sudden reduction of the electron mobility, the electron mobility collapse, in n-type GaN grown by low pressure metalorganic chemical vapor deposition. Secondary ion mass spectroscopy has been performed in conjunction with C concentration and the thermodynamic Ga supersaturation model. By controlling the ammonia flow rate, the input partial pressure of Ga precursor, and the diluent gas within the Ga supersaturation model, the C concentration in Si-doped GaN was controllable from 6 × 1019 cm−3 to values as low as 2 × 1015 cm−3. It was found that the electron mobility collapsed as a function of free carrier concentration, once the Si concentration closely approached the C concentration. Lowering the C concentration to the order of 1015 cm−3 by optimizing Ga supersaturation achieved controllable free carrier concentrations down to 5 × 1015 cm−3 with a peak electron mobility of 820 cm2/V s without observing the mobility collapse. The highest electron mobility of 1170 cm2/V s was obtained even in metalorganic vapor deposition-grown GaN on sapphire substrates by optimizing growth parameters in terms of Ga supersaturation to reduce the C concentration.

Cobalt(I) Olefin Complexes: Precursors for Metal-Organic Chemical Vapor Deposition of High Purity Cobalt Metal Thin Films.

We report the synthesis and characterization of a family of organometallic cobalt(I) metal precursors based around cyclopentadienyl and diene ligands. The molecular structures of the complexes cyclopentadienyl-cobalt(I) diolefin complexes are described, as determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis and thermal stability studies of the complexes highlighted the isoprene, dimethyl butadiene, and cyclohexadiene derivatives [(C5H5)Co(η(4)-CH2CHC(Me)CH2)] (1), [(C5H5)Co(η(4)-CH2C(Me)C(Me)CH2)] (2), and [(C5H5)Co(η(4)-C6H8)] (4) as possible cobalt metal organic chemical vapor deposition (MOCVD) precursors. Atmospheric pressure MOCVD was employed using precursor 1, to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere (760 torr) of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 325, 350, 375, and 400 °C, respectively, by scanning electron microscopy and atomic force microscopy reveal temperature-dependent growth features. Films grown at these temperatures are continuous, pinhole-free, and can be seen to be composed of hexagonal particles clearly visible in the electron micrograph. Powder X-ray diffraction and X-ray photoelectron spectroscopy all show the films to be highly crystalline, high-purity metallic cobalt. Raman spectroscopy was unable to detect the presence of cobalt silicides at the substrate/thin film interface.

Growth mechanism of single-crystalline NiO thin films grown by metal organic chemical vapor deposition

Nickel oxide (NiO) thin films were grown by atmospheric-pressure metal organic chemical vapor deposition (APMOCVD). Growth was carried out using various growth parameters, including the growth temperature, the input precursor (O2/Ni) ratio, and the type of substrate material. Effects of the growth parameters on the structural and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the crystal structure and quality were strongly affected by the growth temperature and the type of substrate material. At an optimized growth temperature, single-crystalline NiO films were grown on MgO(100) and MgO(111) substrates in a cube-on-cube orientation relationship, while on an Al2O3(001) substrate, the film was grown in the NiO[111] direction. The use of MgO substrates successfully suppressed the formation of twin defects, which have been frequently reported in the growth of NiO. The difference in the formation of the twin defects on MgO and Al2O3 substrates was discussed. It was observed that the resistivity dependence on crystal quality was affected by the choice of substrate material. The effects of the precursor ratio on the transmittance and resistivity of the films were also investigated. Improved transparency in the visible wavelength region and higher conductivity were found in films grown with higher O2/Ni ratios.