Metalorganic Chemical Vapor Deposition Technique Research Articles

Influence of annealing on the structural and optical properties of ZnO films grown by MOCVD

The properties of ZnO films grown on Si (1 1 1) substrates by Metal-Organic Chemical Vapor Deposition technique using diethylzinc and H 2O as reactant gases are reported. The primary focus is on understanding the origin of deep-level luminescence. As increasing the annealing temperature, a visible emission is observed both in samples annealing in oxygen atmosphere and nitrogen atmosphere. In addition, this broad defect emission becomes obviously asymmetric when the annealing temperature was increased to 1000 °C in oxygen atmosphere. Theoretical investigations have reported that the formation enthalpy of defects is varied under different conditions. With these results, it is suggested that the visible emission in ZnO films annealed in oxygen atmosphere is related to zinc vacancy and oxygen interstitial defects. While, the green emission in ZnO films which were annealed in nitrogen atmosphere is attributed to oxygen vacancy defects.

The growth behavior of GaN NWs on Si(1 1 1) by the dispersion of Au colloid catalyst using pulsed MOCVD

We report on the growth of self-assembled GaN nanowires (NWs) on Si(1 1 1) substrates via pulsed metal-organic chemical vapor deposition (MOCVD) technique. Au colloid nanoparticles dispersed on Si(1 1 1) substrate were used as catalyst to conduct the GaN NWs growth. The size of the GaN NWs can be tailored by an easy and simple method of optimizing the Au colloids catalyst using Ga pre-deposition. The pulsed MOCVD growth mode was used to grow GaN NWs in which the group III and group V precursors were introduced alternately in the sequence. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL). The XRD pattern confirmed the hexagonal structure of GaN NWs. The experimental results indicated that the GaN NW diameter depended on the size of Au+Ga droplets. The pulsed method combined with growth temperature considerably affected the shape and density of the GaN NWs.

Spectroscopic ellipsometry studies on the optical constants of Bi4Ti3O12:xNa thin films grown by metal-organic chemical vapor deposition

We have deposited undoped and Na-doped epitaxial Bi4Ti3O12 thin films on SrTiO3(001) substrates using the liquid-delivery spin metal-organic chemical vapor deposition technique. High resolution x-ray diffraction and Raman spectroscopy measurements were employed to investigate the structural perfection and incorporation of Na ions into the film. The ellipsometric measurements were carried out in the energy range 1.49–2.75eV and the corresponding experimental data were fitted. Two different dispersion relations, Cauchy's absorbent and Tauc-Lorentz, have been used to determine the optical constants of the films. It is observed that there is a decrease in optical band gap for increasing sodium content. Furthermore, it has been found that the refractive index and extinction coefficient also depend on the sodium content. The refractive index dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters were determined. The optical constants tend to decrease with increasing doping content.

Fabrication of hydroxyapatite film on Ti–29%Nb–13%Ta–4.6%Zr using a MOCVD technique

A hydroxyapatite (HAp) film was fabricated on the surface of Ti–29Nb–13Ta–4.6Zr (TNTZ) using a metal-organic chemical vapor deposition (MOCVD) technique, and the mechanical biocompatibility and HAp formability of HAp-coated TNTZ were evaluated and discussed in this study. HAp film is fabricated on the surface of TNTZ by controlling the heating temperature of the source bis-dipivaloylmethanatocalcium ((Ca(dpm)2) and (C6H5O)3PO). An α-phase precipitates in the TNTZ matrix after heating the substrate, and the mechanical properties and Young's modulus of HAp-coated TNTZ are improved. HAp-coated TNTZ maintains excellent mechanical biocompatibility. The formability of HAp on HAp-coated TNTZ in Hank's balanced salt solution is better than that of HAp on non-coated TNTZ.

Chemical vapor deposition and characterization of high-k BaHf1−xTixO3 dielectric layers for microelectronic applications

Possibilities to grow high-k BaHf1−xTixO3 layers were investigated by pulsed liquid injection metal-organic chemical vapor deposition technique. Ba(thd)2 (thd=2,2,6,6-tetramethylheptane-3,5-dionate), Hf(thd)4, and Ti(OiPr)2(thd)2 were used as precursors, toluene as solvent, and Si(100) as substrate. The influence of solution composition and deposition temperature on crystallization and elemental and phase compositions of Ba–Hf–Ti–O layers was investigated. BaHf1−xTixO3 layers with x∼0–0.5 may be obtained at 600–650 °C, whereas the lower deposition temperature (500–550 °C) resulted in crystallization of the dominating orthorhombic BaCO3 phase in deposited films. Films were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electrical measurements were performed for deposited thin films in view of storage capacitor applications of BaHf1−xTixO3 films in dynamic random access memories.

Photoluminescence properties of Eu3+ ions in Eu‐doped ZnO grown by sput‐ tering‐assisted metalorganic chemical vapor deposition

AbstractPhotoluminescence (PL) properties of Eu‐doped ZnO (ZnO:Eu) grown by a sputtering‐assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements under the high‐energy excitation above the band‐gap energy of ZnO (indirect‐excitation) at room temperature, the annealed sample showed clear red‐emission lines due to the intra‐4f shell transition of 5D0→7F2 in Eu3+. Under the low‐energy excitation resonant to the energy levels of 7F0–5D3 transitions (direct‐excitation), additional PL lines which showed fast thermal quenching were observed. These results revealed that the energy transfer from ZnO host to Eu3+ was accompanied, but there were inactive Eu3+ ions under the indirect‐excitation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence Properties of Non-Tapered InN Nanorods Grown by Plasma-Assisted Metalorganic Chemical Vapor Phase Deposition

We have successfully grown non-tapered InN nanorods on Si substrate using an RF plasma assisted metalorganic chemical vapor deposition technique. Employment of 50 W nitrogen plasma reduces the optimal growth temperature to 500 degrees C. In order to study the temperature dependent bandgap and thermal quenching mechanism in relation to the localized states, photoluminescence measurement over a temperature range from 7 to 160 K are conducted. The photoluminescence at 7 K shows a strong near-band-emission energy of 0.682 eV with a narrow band width of 0.027 eV, which reveals excellent optical and structural qualities of the InN nanorods.

ChemInform Abstract: Volatile Barium β-Diketonates for Use as MOCVD Precursors

Metal-organic chemical vapor deposition (MOCVD) techniques have been used to deposit thin superconducting films of YBa2Cu3O7-x. A limitation of the technique lies in the volatility of the barium(II) precursors. A review of attempts to enhance volatility through substitution of fluorinated chelating agents and studies to limit oligomerization of the barium chelates are reviewed. Within the past five years, substantial progress has been made in synthesizing more volatile barium complexes, and the most volatile barium compound yet reported is a monomeric chelate in which five hexafluoroacetylacetonato ligands are bonded to barium(II).

Strain and crystal defects in thin AlN/GaN structures on (0001) SiC

High-resolution x-ray diffraction was used to compare strain relaxation and defect populations in thin GaN/AlN heterostructures (total thickness ≈480 nm) grown on (0001) SiC using metalorganic chemical vapor deposition (MOCVD) and hydride vapor epitaxy (HVPE) techniques. The results of high-resolution x-ray diffraction measurements (rocking curves and reciprocal space mapping) were corroborated using transmission electron microscopy. Differently grown films exhibited dissimilar strain relaxation and defect populations that were related to specific growth conditions. In the MOCVD films, grown under lower deposition rates, the elastic strain in the AlN and GaN layers was fully relaxed at the initial stages of the epitaxial growth yielding nearly similar densities of threading dislocation segments (TDS) in layer volumes. Additional, “secondary” elastic stresses in these layers were attributed to the excess of point defects. In the HVPE films, grown under higher (five to ten times) deposition rates, these layers were over relaxed and the density of TDS in the GaN layer was an order of magnitude larger than that in AlN. The MOCVD-grown sample was devoid of planar defects whereas the HVPE film contains significant densities of stacking faults in both GaN and AlN layers. Formation of “secondary” extended defects was interpreted in terms of creation and structural transformation of point defects during epitaxial growth. Differences in strain levels, types, and defect populations/distributions for the two heterostructures were attributed to the different growth rates for MOCVD and HVPE.

Preparation of ZnO thin films using MOCVD technique with D 2O/H 2O gas mixture for use as TCO in silicon-based thin film solar cells

Zinc oxide (ZnO) thin films have been successfully grown by metal organic chemical vapor deposition (MOCVD) technique using deuterium water (D 2O) and water (H 2O) mixtures as oxidants for diethylzinc (DEZ). B 2H 6 was also employed as a dopant gas. It was found that the crystal orientation of ZnO films strongly depends on D 2O/H 2O ratio. As a result, the surface morphology of ZnO changed from textured surface morphology to smooth surface morphology with increase in the ratio of D 2O/H 2O. Moreover, it was also observed that the carrier concentration of ZnO films did not change with the ratio of D 2O/H 2O, while the mobility of these films was strongly dependent on the D 2O/H 2O ratio. Without D 2O addition, the resistivity of films had its lowest value and the minimum sheet resistance was 10 Ω/square. All films showed transmittance higher than 80% in the visible region. Moreover, the haze values of these films could be controlled by the ratio of D 2O/H 2O. These results indicate that the crystal orientation and surface morphology of the low resistivity ZnO films can be modified by using a mixture of D 2O and H 2O without changing the deposition temperature. Thus, the obtained ZnO films are promising for use as a front TCO layer in Si-based thin film solar cells.

MOCVD Preparation and Photoluminescence of ZnS Nanowires

An original MOCVD reactor was developed to grow zinc sulphide nanowires. The design of a heater system to have an improved control of the process and to obtain homogenous deposition was performed. ZnS nanowires were successfully synthesized by simple metal-organic chemical vapor deposition technique from ZnS powders onto silicon substrates [111]. Substrates were carried out to a process of cleaning and impregnated with gold clusters from a colloidal solution. Field emission scanning electron microscope (FESEM) observations show that the ZnS nanowires have diameters about 10-20 nm and lengths up to several micrometers. Photoluminescence (PL) properties of these synthesized single-crystal ZnS nanowires have been presented. Finally PL detects peaks related to the nanosize effects of the ZnS nanowires.

Electron Paramagnetic Resonance Studies of Shallow Donors Behavior in Hydrogenated ZnO Films

Photoassisted metalorganic chemical vapor deposition (photo-MOCVD) technique was used for depositing of as-grown (ZnO) and hydrogenated (ZnO:H) zinc oxide polycrystalline thin films under different growth and hydrogen doping conditions. The structure and morphology of the films was controlled using SEM and AFM microscopy and surface roughness measurements. The studies of paramagnetic defects behavior and magnetic susceptibility in as-grown and hydrogenated samples were provided in the temperature range 77-300 K using X-band EPR spectrometer. It was found that all the samples exhibited a single symmetric strong Lorentzian line at g = 1.96 while the line intensity was shown to increase upon H-doping. The concentration of paramagnetic defects, associated with the concentration of the hydrogen donors, was extracted. The behavior of the magnetic susceptibility curves was described by Curie and Pauli contributions. We have shown that the excess concentration of paramagnetic defects, appeared after hydrogen doping, correlated with the increase of the Pauli term of magnetic susceptibility and followed the increase of free carrier concentration

METAL ORGANIC CHEMICAL VAPOR DEPOSITION OF MONOLITHIC AND FUNCTIONALLY GRADED BST FILMS

ABSTRACT Thin films of barium-strontium-titanate (BST) can serve as the tunable dielectric in a variety of RF and microwave devices. Compositionally graded BST films optimize films for the highest permittivity, highest tunability, maximum temperature stability, and minimum dielectric loss. This paper describes recent work to deposit BST films using a dual injection, metal organic chemical vapor deposition (MOCVD) technique. Injecting two separate precursor solutions (one for Ba-Ti oxide and one for Sr-Ti oxide) provides easy adjustment of the Ba/Sr ratio in the film. The dual injection MOCVD technique can also be extended to a wide range of other complex oxide systems.

Photoluminescence properties of Eu-doped ZnO films grown by sputtering-assisted metalorganic chemical vapor deposition

Photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) grown by a sputtering-assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements at 300 K, the samples annealed at 600 °C for 30 min showed clear red-emission lines due to the intra-4f shell transition of 5 D 0→ 7 F J ( J=0–4) in Eu 3+. In photoluminescence excitation (PLE) spectra, the PL was observed under the high-energy excitation above the band-gap energy of ZnO (indirect excitation) and the low-energy excitation resonant to the energy levels of 7 F 0– 5 D 3 and 7 F 0– 5 D 2 transitions in Eu 3+ (direct excitation). The PL lifetime under the indirect excitation was shorter than that under the direct excitations. These PL properties revealed that the energy transfer from ZnO host to Eu 3+ was accompanied under indirect excitation.

Residual Stress of Free-Standing Membranes of Yttria-Stabilized Zirconia for Micro Solid Oxide Fuel Cell Applications

The present study is devoted to analyze the compatibility of yttria-stabilized zirconia thin films prepared by pulsed laser deposition and metalorganic chemical vapor deposition techniques, with microfabrication processes based on silicon technologies for micro solid oxide fuel cells applications. Deposition of yttria-stabilized zirconia on Si/SiO2/Si3N4 substrates was optimized for both techniques in order to obtain high density and homogeneity, as well as a good crystallinity for film thicknesses ranging from 60 to 240 nm. In addition, stabilized zirconia free-standing membranes were fabricated from the deposited films with surface areas between 50 x 50 microm2 and 820 x 820 microm2. Particular emphasis was made on the analysis of the effect of the nature of the deposition technique and the different design and fabrication parameters (membrane area, thickness and substrate deposition temperature) on the residual stress of the membranes in order to control their thermomechanical stability for application as electrolyte in micro solid oxide fuel cells.

Photoluminescence Properties of Eu-Doped ZnO Grown by Sputtering-Assisted Metalorganic Chemical Vapor Deposition

Photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) grown by a sputtering-assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements at 300K, the samples annealed at 600°C for 30min showed clear red-emission lines due to the intra-4f shell transition of 5D0→7FJ (J = 2, 3) in Eu3+. In photoluminescence excitation (PLE) spectra, the PL were observed under the high-energy excitation above the band-gap energy of ZnO (indirect excitation) and the low-energy excitation resonant to the energy levels of 7F0-5D3 and 7F0-5D2 transitions in Eu3+ (direct excitation). These results revealed that the energy transfer from ZnO host to Eu3+ was accompanied under indirect excitation in ZnO:Eu.

Fabrication of Hydroxyapatite Film on Ti-29Nb-13Ta-4.6Zr Using a MOCVD Technique

A hydroxyapatite (HAp) film was fabricated on the surface of Ti-29Nb-13Ta-4.6Zr (TNTZ) using a metal-organic chemical vapor deposition (MOCVD) technique, and the mechanical biocompatibility and HAp formability of HAp-coated TNTZ were evaluated and discussed in this study. HAp film is fabricated on the surface of TNTZ by controlling the heating temperature of the source (bis-dipivaloylmethanatocalcium (Ca(dpm)2) and (C6H5O)3PO). An α-phase precipitates in the TNTZ matrix after heating the substrate, and the mechanical properties and Young’s modulus of HAp-coated TNTZ are improved. HAp-coated TNTZ maintains excellent mechanical biocompatibility. The formability of HAp on HAp-coated TNTZ in Hank’s balanced salt solution is better than that of HAp on non-coated TNTZ.

Extension of Usable Spectral Range of Peltier Cooled Photodetectors

This paper provides update on development of the Peltier cooled detectors optimized for wavelengths above 13 „m. Initially, the devices made by Vigo were mostly used for uncooled detection of CO2 laser radiation. Over the years the performance and speed of response has been steadily improved. At present the uncooled or Peltier cooled photodetectors can be used for sensitive and fast response detection in the mid-wavelength and long-wavelength infrared spectral range. The devices have found important applications in IR spectrometry, quantum cascade laser based gas analyzers, laser radiation alerters and many other IR systems. Recent eorts were concentrated on the extension of useful spectral range to > 13 „m, as required for its application in Fourier transform IR spectrometers. This was achieved with improved design of the active elements, use of monolithic optical immersion technology, enhanced absorption of radiation, dedicated electronics, series connection of small cells in series, and last but not least, applying more ecient Peltier coolers. Practical devices are based on the complex HgCdTe heterostructures grown on GaAs substrates with metal-organic chemical vapor deposition technique with immersion lens formed by micromachining in the GaAs substrates. The results are very encouraging. The devices cooled with miniature 4 stage Peltier coolers mounted in TO-8 style housings show significant response at wavelength exceeding 16 „m.

Effects of well width and growth temperature on optical and structural characteristics of AlN/GaN superlattices grown by metal-organic chemical vapor deposition

AlN/GaN superlattices (SLs) employing various well widths (from 1.5 to 7.0 nm) are grown by metal-organic chemical vapor deposition technique at various growth temperatures (TS) (from 900 to 1035 °C). The photoluminescence (PL), x-ray diffraction, and intersubband (ISB) absorption characteristics of these SLs and their dependency on well width and growth temperature are investigated. Superlattices with thinner wells (grown at the same TS) or grown at lower TS (employing the same well width) are shown to demonstrate higher strain effects leading to a higher PL energy and ISB absorption energy. Simulations are employed to explain the experimental observations. ISB absorptions from 1.04 to 2.15 μm are demonstrated via controlling well width and growth temperature.

Efficient hole transport in asymmetric coupled InGaN multiple quantum wells

InGaN based light emitting devices (LEDs) with asymmetric coupled quantum wells (AS-QWs) and conventional symmetric coupled quantum wells (CS-QWs) active structures were grown by metal-organic chemical vapor deposition technique. The LEDs with AS-QWs active region show improved light emission intensity and reduced forward voltage compared with LEDs with CS-QWs active region. Based on the electroluminescence measurements and the devices structure analysis, it can be concluded that these improvements are mainly attributed to the efficient hole tunneling through barriers and consequently the uniform distribution of carriers in the AS-QWs.