Metalorganic Chemical Vapor Deposition Method Research Articles

EFFECTS OF THE ORGANIC SOLVENT IN CARRIER GAS ON THE PREPARED TiO2 THIN FILM BY METAL-ORGANIC CHEMICAL VAPOR DEPOSITION METHOD

Titanium dioxide ( TiO 2) thin films are prepared on glass substrates by metal-organic chemical vapor deposition (MOCVD) method using the different organic solvents, e.g. ethanol or cyclohexane, in nitrogen carrier gas with different their concentrations. We reported the effects of the each organic solvent in the carrier gas for MOCVD method on the morphology of the composed particles, the thickness, the surface roughness, and the transparency of the prepared TiO 2 thin films with changing the deposition temperature. The morphology of the particles which compose the thin films, and the surface roughness of the prepared TiO 2 thin films are observed and measured by atomic force microscope (AFM) and field emission scanning electron microscopy (FE-SEM). The film thickness is measured by fluorescent X-ray spectroscopy (XRF), and the transparency of the films is confirmed by UV-vis spectroscopy. The transparencies of the TiO 2 thin films differ depending on the MOCVD conditions, e.g. the organic solvents species, the concentration of the container in the carrier gas and the deposition temperatures. We have found that the species and the concentration of the organic solvents in the carrier gas are very important factor to prepare homogeneous TiO 2 thin films by MOCVD method; cyclohexane inhibits to aggregate of the TiO 2 nanoparticles on the glass substrate during the MOCVD process.

Study of Depth-Dependent Tetragonal Distortion of GaN Epilayer with Tri-Layer AlGaN Interlayer Growth on Si(111)

A GaN epilayer with tri-layer AlGaN interlayer grown on Si (111) by metal-organic chemical vapor deposition (MOCVD) method was discussed by synchrotron radiation x-ray diffraction (SRXRD) and Rutherford backscattering (RBS)/C. The crystal quality of the epilayer is very good with a χmin=2.1%. According to the results of the θ-2θ scan of GaN(0002) and GaN(1122), the epilayer elastic strains in perpendicular and parallel directions were calculated respectively to be-0.019% and 0.063%. By the angular scan using RBS/C around a symmetric [0001] axis and an asymmetric [1213] axis in the (1010) plane of the GaN layer, the tetragonal distortion (eT ) were determined to be 0.09%. This result coincides with that from SRXRD perfectly. The strain decreases gradually towards the near-surface layer, which will avoid the film cracks efficiently and improve the crystal quality of the GaN epilayer remarkably.

CexAlyOz/TiN stack analysis for Metal–Insulator–Metal applications: Effect of annealing and the metal electrode deposition method

CexAlyOz thin films were deposited on TiN metal electrode by metalorganic chemical vapour deposition method at 400°C. The detailed physical characterization on CexAlyOz/TiN stack upon annealing at different temperatures (600°C and 850°C) and for different deposition methods (Atomic vapour deposition (AVD) and Physical vapour deposition (PVD)) of electrode material were done for possible Metal–Insulator–Metal applications. X-ray diffraction results exhibited that the dielectric and TiN(AVD) are amorphous while TiN(PVD) is crystalline for the as deposited stacks. Annealing on CexAlyOz/TiN(AVD) at 600°C, initiates CeO2 crystallization in the dielectric with composition of Ce:Al=0.5 as obtained by X-ray photoelectron spectroscopy. In CexAlyOz/TiN(PVD) stack, the dielectric remains in its amorphous state until 850°C. However, TiO2 crystallization is formed at 600°C in CexAlyOz/TiN(PVD). Time of flight secondary ion mass spectroscopy depth profiling data proves that the annealing at 600°C caused the oxidation of both the metal electrodes and the inter-diffusion of Ti from the bottom metal electrode through the dielectric layer.

Lipon thin films grown by plasma-enhanced metalorganic chemical vapor deposition in a N 2–H 2–Ar gas mixture

Lithium phosphorus oxynitride (Lipon) thin films have been deposited by a plasma-enhanced metalorganic chemical vapor deposition method. Lipon thin films were deposited on approximately 0.2 μm thick Au-coated alumina substrates in a N 2–H 2–Ar plasma at 13.56 MHz, a power of 150 W, and at 180 °C using triethyl phosphate [(CH 2CH 3) 3PO 4] and lithium tert-butoxide [(LiOC(CH 3) 3] precursors. Lipon growth rates ranged from 10 to 42 nm/min and thicknesses varied from 1 to 2.5 μm. X-ray powder diffraction showed that the films were amorphous, and X-ray photoelectron spectroscopy (XPS) revealed approximately 4 at.% N in the films. The ionic conductivity of Lipon was measured by electrochemical impedance spectroscopy to be approximately 1.02 μS/cm, which is consistent with the ionic conductivity of Lipon deposited by radio frequency magnetron sputtering of Li 3PO 4 targets in either mixed Ar–N 2 or pure N 2 atmosphere. Attempts to deposit Lipon in a N 2–O 2–Ar plasma resulted in the growth of Li 3PO 4 thin films. The XPS analysis shows no C and N atom peaks. Due to the high impedance of these films, reliable conductivity measurements could not be obtained for films grown in N 2–O 2–Ar plasma.

Heteroepitaxy of ZnO Films on Epi-GaN/Al<sub>2</sub>O<sub>3</sub>(0001) by MOCVD

Single crystalline ZnO thin films have been deposited on epi-GaN/sapphire (0001) substrates by the metalorganic chemical vapour deposition (MOCVD) method. The structural and optical properties of the ZnO films were investigated in detail. The film prepared at 600°C was epitaxial single crystalline with the wurtzite structure of pure ZnO and a single orientation of (0002) direction. High-resolution transmission electron microscopy was used to investigate the interface area, and a clear orientation relationship of ZnO (0001) || GaN (0001) and ZnO [] || GaN [] was obtained. The average transmittance for the samples in the visible range was over 75%.

Selective Palladium‐Loaded MIL‐101 Catalysts

Palladium nanoparticles (NPs) of different mean particle size have been synthesized in the host structure of the porous coordination polymer (or metal-organic framework: MOF) MIL-101. The metal-organic chemical vapor deposition method was used to load MIL-101 with the Pd precursor complex [(η(5)-C(5)H(5))Pd(η(3)-C(3)H(5))]. Loadings higher than 50 wt.% could be accomplished. Reduction of the Pd precursor complex with H(2) gave rise to Pd NPs inside the MIL-101 (Pd@MIL-101). The reduction conditions, especially the temperature, allows us to make size-conform (size of the Pd NPs correlates with the size of the cavities of the host structure of MIL-101) and undersized Pd NPs. The Pd@MIL-101 samples were characterized by X-ray diffraction, IR spectroscopy, Brauner-Emmett-Teller (BET) analysis, elemental analysis, and transmission electron microscopy (TEM). Catalytic studies, hydrogenation of ketones, were performed with selected Pd@MIL-101 catalysts. Activity, selectivity, and recyclability of the catalyst family are discussed.

Evolution of the deformation state and composition as a result of changes in the number of quantum wells in multilayered InGaN/GaN structures

The methods of high-resolution X-ray diffraction have been used to study the multilayered structures in an InxGa1 − xN/GaN system grown by the method of metal-organic chemical-vapor deposition. A correlation between the strain state (relaxation) of the system, the indium content within quantum wells, the ratio of the barrier/well thicknesses, and the number of quantum wells in the active superlattice is established. It is shown that partial relaxation is observed even in a structure with one quantum well. The results we obtained indicate that the relaxation processes are bound to appreciably affect the optical characteristics of devices.

Effects of growth pressure on the properties of p-GaN layers

The influence of growth pressure on the properties of p-GaN grown by metal-organic chemical vapor deposition method was investigated. The p-GaN layers were grown at low temperature under growth pressures ranging from 100 to 400 mbar. We find that higher growth pressure leads to lower Mg incorporation in the p-GaN layer and results in high resistivity of p-GaN grown at 400 mbar. By optimizing the Cp2Mg/TMGa ratio, however, low sheet resistivity can be achieved for p-GaN grown at 100–300 mbar. The p-GaN grown at 300 mbar using optimal Cp2Mg/TMGa ratio of 1.3% shows the highest hole concentration of 5.0×10 17 cm −3 and the consequent minimum sheet resistivity of 2.6×10 4 Ω/sq. The superior electrical properties are ascribed to the reduction of compensation effect for the layer grown under the high growth pressure.

Epitaxial lateral overgrowth of GaN on sapphire substrates using in-situ carbonized photoresist mask

Epitaxial lateral overgrowth (ELO) GaN samples were successfully grown on masked sapphire (0 0 0 1) substrates using an in-situ carbonized photoresist (PR) mask by a metalorganic chemical vapor deposition (MOCVD) method. The PR masks for the ELO process were prepared using conventional lithography in the form of a stripe with an opening of 4 μm and a period of 16 μm. The stripe-patterned PR was annealed at 1000 °C in a H 2 atmosphere. The stripes were aligned parallel to the [ 1 1 − 2 0 ] Al 2 O 3 direction. The ELO process of GaN was strongly dependent on the direction of the stripes. Overall, the PR masks on the sapphire substrate were carbonized during the heating step before the main growth, so that the carbonized PR mask acted as an ELO mask. The study results confirmed the promising potential of the ELO process using an in-situ carbonized PR mask as a single-step technique.

Influence of thermally diffused aluminum atoms from sapphire substrate on the properties of ZnO epilayers grown by metal-organic chemical vapor deposition

In this study, the authors investigate the evolution of the structural and electrical properties of ZnO epilayers grown by the metal-organic chemical vapor deposition method on c-sapphire substrates. The inserting of a low-temperature ZnO buffer layer not only significantly improves the structural quality of the high-temperature (HT)-grown ZnO epilayer on a sapphire substrate but also results in high background electron concentration in it from the Hall-effect measurement. After subtracting the conductive contribution from a thin degenerated layer mostly formed between the buffer layer and the substrate based on the two-layer model, the deduced electron-carrier concentration is still in the order of 1018 cm−3, which is much larger than the 1016 cm−3 obtained from capacitance-voltage measurement near the top surface. This indicates that a much thicker layer with high carrier concentration should be formed in the HT-grown ZnO epilayer, which is significantly different from that observed in GaN epitaxy, where only a thin degenerated interfacial layer is suggested to form in the GaN buffer layer. Al atoms’ distribution acquired from secondary-ion mass spectrometry shows a strong dependence on the temperature of the ZnO growth process, indicating that a thermally enhanced diffusion mechanism should be responsible for the observation of the enhanced Al atom concentration in the HT-grown ZnO epilayer. As substituted Al atoms on the Zn site act as donors in ZnO, the one-to-one correspondence between Al content and the carrier concentration, as well as the analysis of temperature-dependent Hall-effect measurement, indicates that diffusion-induced gradient-distributed AlZn shallow donors should be the main origin of the high background-carrier concentration in the HT-grown ZnO epilayers.

Growth Behavior and Characteristics of One Dimensional ZnO Nanostructures by Metalorganic Chemical Vapor Deposition

The ZnO nanorods have been grown on silicon substrates by a metalorganic chemical vapor deposition (MOCVD) process with/without Au catalytic layer. The growth behavior of ZnO nanorods changed with the catalytic layer. The presence of Au catalyst complicated the growth direction of ZnO nanorods in the MOCVD methods. The ZnO nanorods had single crystalline atomic structure and pure compositions without impurities and strong and narrow excitonic emission. We investigated the growth behavior of the ZnO nanostructures which are leading candidate for optical applications.

The explanation of InN bandgap discrepancy based on experiments and first-principle calculations

Indium nitride (InN) films with different free electron concentration and optical bandgap were grown either directly on sapphire substrate or on pre-covered gallium nitride (GaN) buffer through metal-organic chemical vapor deposition (MOCVD) method. Based on first-principle calculations, we confirm that the widening of InN optical bandgap reported before is caused by high density of free electrons. To find the contributor of the free electrons, the characteristic energetic levels of ON, VN and SiIn are investigated. We find that they are all high enough to uplift the optical bandgap from about 0.78 eV to 1.9 eV, which almost can't be enlarged further when it reaches 2.09 eV.

Influence of Na on the structure of Bi 4Ti 3O 12 films deposited by liquid-delivery spin MOCVD

Thin Na-substituted Bi 4Ti 3O 12 films were grown by the liquid-delivery spin metal-organic chemical vapor deposition (MOCVD) method with different concentrations of sodium bis(trimethylsilyl)amide [Na(TMSA)] as Na precursor. At a substrate temperature of 600 °C the original Aurivillius structure was preserved, however high resolution x-ray diffraction (HRXRD) studies indicate that the Na-substituted phase exhibits a slightly smaller lattice parameter compared to the pure Bi 4Ti 3O 12 phase. From additional x-ray photoemission spectroscopy (XPS) results, we have concluded that monovalent Na + ions have been incorporated on Bi 3+ sites in the perovskite units. The proposed charge compensation for this aliovalent substitution is explained by a shift of the valence state of Bi 3+ ions in the vicinity of the incorporated Na + ions from 3+ to 5+. Due to the small ionic radius of the Bi 5+ ions, the incorporation efficiency amounts to a few atomic percent only.

Plasma-Enhanced Metalorganic Chemical Vapor deposition of Lipon Thin Films

ABSTRACTLithium phosphorus oxynitride (Lipon) thin films have been deposited by a plasmaenhanced metalorganic chemical vapor deposition (PE-MOCVD) method using triethyl phosphate [(CH2CH3)3PO4] and lithium tert-butoxide [(LiOC(CH3)3] precursors. Growth rates were between 100 and 415 Å/min, and thicknesses ranged from 1 to 2.5 μm. X-ray powder diffraction showed that the films were amorphous, and X-ray photoelectron spectroscopy revealed approximately 6.9 at.% carbon in the films. The ionic conductivity of Lipon was measured using electrochemical impedance spectroscopy (EIS) and approximately 1.02 μS/cm was obtained, which is consistent with the ionic conductivity of Lipon deposited by radio frequency magnetron sputtering of Li3PO4 targets. An all-solid-state thin-film lithium microbattery such as Li/Lipon/LiCoO2/Au/substrate was successfully fabricated with Lipon deposited by PE-MOCVD. The battery has a capacity of ca. 22 μAh/cm2μm.

Transparent Conducting ZnO:Ga Epitaxial Films Prepared on Epi-GaN/Al<sub>2</sub>O<sub>3</sub> (0001) by MOCVD

High-quality Gallium-doped zinc oxide (ZnO:Ga) films have been prepared on epi-GaN/sapphire (0001) substrates by the metalorganic chemical vapour deposition (MOCVD) method. The relative amount of gallium doping was varied from 0 to 8% (atomic ratio). The structural, electrical and optical properties of the ZnO:Ga films have been investigated in detail, as a function of Ga content. All the prepared samples have the wurtzite structure of pure ZnO with a strong (0002) preferred orientation. The microstructure for the surface of films was markedly influenced by the amount of Ga doping. The resistivity decreases continuously with adding Ga content and reaches to the value of 8.4×10-3 Ω•cm at 8%. The average transmittance for the deposited ZnO:Ga samples in the visible range was over 75%.

Preparation and characterization of single crystalline SnO2 films deposited on TiO2 (0 0 1) by MOCVD

Tin oxide (SnO2) epitaxial thin films have been prepared on TiO2 (001) substrates at different temperatures by metalorganic chemical vapor deposition (MOCVD) method. The obtained films were pure SnO2 with the tetragonal rutile structure. An in-plane orientation relationship of (001) SnO2‖(001) TiO2 with [100] SnO2‖[100] and [010]SnO2‖[010]TiO2 between the film and substrate was determined. The SnO2 film prepared at 600°C presented the best single crystalline structure. The average transmittance of the SnO2 samples in the visible range exceeded 68%. In the photoluminescence spectra, a broad luminescence band centered at 615nm was observed.

Zero-dimensional field emitter based on ZnO quantum dots

ZnO quantum dots (QDs) with diameter around 6 nm were grown by a catalyst-free metalorganic chemical vapor deposition method and applied as electron field emitters. The Ga doping resulted in a considerable improvement of the field emission properties. Macroscopic field emission measurements revealed that the Ga-doped ZnO QDs have a low turn-on field of 1.3 V/μm and a large field enhancement factor up to 104. Probe force microscopy and scanning field emission probe microscopy were used for mapping at submicrometer scale of the spatial distribution of the work function and the field emission, respectively. The local measurements indicated a spatial correlation between both properties that could be linked to spatial variations of the Ga doping level.

Invariable optical properties of phosphor-free white light-emitting diode under electrical stress

This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours' current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode.

Structural, optical and electrical properties of Al–N codoped ZnO films by RF-assisted MOCVD method

N-doped ZnO films were produced using N 2 as N source by metal-organic chemical vapor deposition (MOCVD) system which has been improved with radio-frequency (RF)-assisted equipments. The data of secondary ion mass spectroscopy (SIMS) indicate that the concentration of N in N-doped ZnO films is around 5 × 10 20 cm −3, implying that sufficient incorporation of N into ZnO can be obtained by RF-assisted equipment. On this basis, the structural, optical and electrical properties of Al–N codoped ZnO films were studied. Then, the effect of RF power on crystal quality, surface morphologies, optical properties was analyzed using X-ray diffraction, atomic force microscopy and photo-luminescence methods. The results illustrate that the RF plasma is the key factor for the improvement of crystal quality. Then the observation of A 0X recombination associated with N O acceptor in low-temperature PL spectrum proved that some N atoms have occupied the positions of O atoms in ZnO films. Hall measurements shown that p-type ZnO film deposited on quartz glasses was obtained when RF power was 150 W for the Al–N codoped ZnO films, while the resistivity of N-doped ZnO films was rather high. Compared with the Al-doped ZnO film, the obviously increased resistivity of codoped films indicates that the formation of N O acceptors compensate some donors in ZnO films effectively.

Room‐temperature ferromagnetism in V‐doped GaN thin films grown by MOCVD

AbstractV‐doped GaN thin films were grown on c‐sapphire substrate by metal organic chemical vapour deposition method (MOCVD). We have used vanadium tetrachloride (VCl4) to intentionally incorporate vanadium (V) during the crystal growth of GaN. X‐ray diffraction measurements revealed no secondary phase in the samples.Magnetic experiments using superconducting quantum interference device (SQUID) showed clear hysteresis loop in magnetization versus applied field (M –H) curves for V‐doped GaN films. The ferromagnetic behavior was evidenced at 300 K, implying the Curie temperature to be over 300 K. Strong and broad blue‐luminescent band (centered at 2.6 eV) is induced by the V doping in GaN. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)