Pulsed MOCVD Research Articles

Preparation of thin films of platinum group metals by pulsed MOCVD. I. Deposition of Ir layers

Preparation of thin films of platinum group metals by pulsed MOCVD. I. Deposition of Ir layers

Dislocation reduction in high Al‐content AlGaN films for deep ultraviolet light emitting diodes

AbstractWe report a new approach for growing thicker (>2 µm) low‐defect AlGaN layers over sapphire using pulsed MOCVD procedure. These high content AlGaN layers serve as templates for subsequent n‐AlGaN growth for deep ultraviolet light emitting diodes (DUV LEDs). During the growth of the AlxGa1−xN layer, the pulsed‐growth conditions were cyclically adjusted to reduce the dislocations. This leads to AlGaN templates with an RMS roughness of 9.6 Å and (102) off‐axis X‐ray line‐width 550 arcsec. The transmission electron microscope (TEM) analysis shows 4 × 107 cm−2 edge type and 2 × 106 cm−2 screw type of threading dislocation densities at best regions. On the average dislocation density in these films is 4 × 108 cm−2. A light emitting diode (LED) structure emitting at 280 nm was deposited on these templates. A comparative study showed the EL emission for LEDs on the new low‐defect templates to be more than 1.6 times stronger than our conventional DUV LED structures. In this paper the details of our growth procedure, the epi‐structure X‐ray, atomic force microscopy (AFM), TEM, and other characterizations will be presented. A comparative study of DUV LED structures over conventional and improved templates of this work will be discussed.

Pulsed MO CVD Processes of MgO Layer Deposition from Mg(thd)2

Dipivaloylmethane was used as a precursor to deposit MgO layers on polished silicon (100) plane in a hot-wall pulsed MO CVD reactor. A detailed investigation of the thermal parameters of the precursor was carried out to optimize the conditions for film deposition experiments. Temperature dependencies of vapour pressure were measured using the flow procedure and Knudsen's method with the mass spectrometric identification of the composition of the gas phase. The processes of Mg(thd)2 decomposition in vacuum, in oxygen and in water vapour were investigated by means of high-temperature mass spectrometry. The major products of precursor decomposition were established; the mechanism of its decomposition was proposed. Investigation of the deposition of MgO layers was carried out within the substrate temperature range 350-450оС, source temperature 190÷210оC in the presence of oxygen. The resulting layers were characterized using AFM, ellipsometry, XRD. The morphology, structure and secondary electron emission of MgO films were investigated.

Pulsed MOCVD Processes of MgO Layer Deposition from Mg(thd)2

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Selective area heteroepitaxy of low dimensional a ‐plane and c ‐plane InGaN nanostructures using pulsed MOCVD

AbstractHigh density a ‐plane and c ‐plane InGaN nanostructures have been developed by nanoscale selective area epitaxial growth using pulsed MOCVD. SiO2 was used as a mask with nanopatterning through an anodic aluminum oxide template. The lateral dimensions of the pattern were controlled and varied from 30 nm to 180 nm by changing the anodization voltage and the electrolyte. Different substrates such as a ‐plane GaN on r ‐plane sapphire, r ‐plane sapphire and c ‐plane sapphire were used to develop InGaN nanostructures in a ‐ and c ‐ crystallographic directions respectively. Under identical growth conditions, InGaN nanostructures of various shapes were obtained on different substrates with differences in emission wavelength. The shape of the nanostructures on different substrates is discussed with respect to the stability and growth rates of various planes. However, the difference in emission wavelength is attributed to the In incorporation in the nanostructures. The optical properties of the nanostructures were studied by photoluminescence (PL) spectroscopy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

La2Zr2O7 single buffer layer for YBCO RABiTS coated conductors

Chemical deposition methods like MOD and MOCVD are promising approaches forcoated conductors (CCs) due to their reduced cost and easy scaling. High qualityLa2Zr2O7 (LZO) buffer layers were prepared by MOD on Ni–5 at.% W (NiW)RABiTS and subsequent YBCO layers (450–800 nm thick) were depositedby pulsed injection MOCVD, leading to a simple low cost architectureNiWRABiTS/LZOMOD/YBCOMOCVD. In this novel combination of MOD and MOCVD approaches, a singleLZOMOD buffer layer is sufficient to ensure structural compatibility between YBCO andNiW, and protect the substrate from oxidation during YBCO MOCVD. YBCOfilms were epitaxially grown on LZO and exhibited critical current densitiesJc close to1 MA cm−2 at 77 K with acritical temperature Tc = 91 K and ΔTc<1 K.

Ferroelectric PbTiO 3 films grown by pulsed liquid injection MOCVD

The influence of deposition conditions (pressure, growth rate, solution concentration, etc.) on the growth of ferroelectric PbTiO 3 films by pulsed liquid injection MOCVD was examined. Pb(thd) 2 and Ti(O iPr) 2(thd) 2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in toluene were used as precursors. Films were grown on LaAlO 3 (001) substrates for deposition process optimisation. PbTiO 3/La 1 − x Sr x MnO 3/LaAlO 3 heterostructures were elaborated at optimized deposition conditions. The microstructure of the heterostructures was characterized by X-ray Diffraction and by Raman spectroscopy. Pt/PbTiO 3/La 1 − x Sr x MnO 3/LaAlO 3 structures were used for ferroelectric, dielectric and piezoelectric characterisations of PbTiO 3 films.

Ferroelectric PbTiO3 films grown by pulsed liquid injection MOCVD

Ferroelectric PbTiO3 films grown by pulsed liquid injection MOCVD

Growth and characterisation of CaCu2Ox thin films by pulsed injection MOCVD

Oxides with the structure MCu2O2 (M=Ca, Ba, Mg and Sr) are promising materials for the development of new p-type transparent conducting oxide thin films. This paper reports preliminary results on the growth and characterisation of CaCu2Ox thin films by pulsed injection MOCVD. By using as precursors calcium and copper tetramethylheptanedionate dissolved in meta-xylene, mixed calcium–copper films have been grown in the temperature range from 450 °C to 550 °C. At these temperatures, deposited films exhibited a high mirror reflection effect, good adherence and were reasonably uniform with the cationic composition of the films being easily controlled by adjusting the copper–calcium ratio in the precursor solution. In CaCu2O2, copper is in the Cu1+ oxidation state and depending on the oxygen partial pressure used, the films either contained CaCu2O3 or a mixture of CaO, CuO and Cu2O. Optimisation of annealing conditions increased the presence of Cu1+ in the film. Films had a maximum transmittance of 50% in the visible range and were highly resistive. Appropriate annealing conditions reduced the resistivity of the films.

Surface morphology of nanostructured anatase thin films prepared by pulsed liquid injection MOCVD

Nanostructured anatase thin films were prepared by chemical vapor deposition feeding a metal organic precursor in a pulsed liquid injection mode. The films were deposited at 500 °C on stainless steel substrates using a single molecular titanium isopropoxide liquid solution as the precursor, without any reactant gas. An effective pulsing injection mechanism for the precursor supply provides uniform concentration of the precursor in the vapor phase, allowing the formation of titanium dioxide layers from small micro-doses of the metal organic precursor. Energy-dispersive spectroscopy, scanning electron microscopy and X-ray diffraction studies show the formation of crack-free nanostructured anatase thin films, highly oriented, formed basically by stepwised nanostructures with a uniform coverage and no detectable carbon contamination. Surface crystallinity, composition, nanostructure and morphology are discussed in terms of the experimental parameters used in the deposition process.

The Controlled Growth of GaN Nanowires

This paper reports a scalable process for the growth of high-quality GaN nanowires and uniform nanowire arrays in which the position and diameter of each nanowire is precisely controlled. The approach is based on conventional metalorganic chemical vapor deposition using regular precursors and requires no additional metal catalyst. The location, orientation, and diameter of each GaN nanowire are controlled using a thin, selective growth mask that is patterned by interferometric lithography. It was found that use of a pulsed MOCVD process allowed the nanowire diameter to remain constant after the nanowires had emerged from the selective growth mask. Vertical GaN nanowire growth rates in excess of 2 mum/h were measured, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the nanowires. The paper reports transmission electron microscopy and photoluminescence data.

MOCVD growth of HfSi xO y films from hafnium β-diketonato silylamides and siloxides

New hafnium β-diketonato-silylamide and siloxides namely Hf(thd) 2[N(SiMe 3) 2] 2 (1), Hf(thd) 2(OSiMe 3) 2 ( 2) and Hf(thd) 2(OSi tBuMe 2) 2 ( 3) (thd=2,2,6,6-tetramethyl-3,5-heptanedionate) were investigated as single-source precursors for low-pressure pulsed liquid injection MOCVD of HfSi x O y thin films on Si(1 0 0) and R-plane sapphire. Films were characterized by XRD, XPS and AFM. The growth rate increased in order 1> 2> 3 in agreement with the decreasing precursor thermal stability. The activation energy was ∼80–100 kJ/mol. The as-deposited at 550–800 °C films were essentially amorphous; hafnia reflections appeared after 1 h annealing at 900 °C probably due to phase separation into amorphous Si-rich silicate and crystallized HfO 2. The surface of the films showed similar amounts of Hf and Si (∼1:1) and was overstoichiometric in oxygen (ratio O/(Hf+Si) >2). The bulk of the films was Hf-rich (70–85% of Hf/ Hf+Si) and slightly oxygen-deficient. The new complexes are attractive single-source precursors for the deposition of pure and very smooth ( R a∼0.7 nm, <1% relative to thickness) HfSi x O y films. Dielectric constant 11.3 and leakage current density 8×10 −4 A/cm 2 (at −1 V) were measured for a 22 nm thick film.

Deposition of MgO thin film by liquid pulsed injection MOCVD

NaCl-type magnesium oxide layers were fabricated using the pulsed liquid-injection metal-organic chemical vapour deposition technique. The deposition has been carried out in oxidizing conditions at atmospheric or sub-atmospheric pressure (10 3 Pa) using a single molecular source: magnesium [bis(2,2,6,6-tetramethyl-3,5-heptanedionate)] (Mg(thd) 2). The structure, composition and morphology of the magnesia films were analysed by X-ray diffraction, Rutherford Backscattering technique (RBS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The surfaces were analysed by X-ray Photoelectron Spectroscopy (XPS). Among the various deposition conditions, the temperature of the substrate and the oxygen flow rate were shown to be the most critical for determining growth rates, morphology and composition.

Synthesis and characterisation of Hf(thd) 2X 2 derivatives [X = N(SiMe 3) 2, OSiMe 3 and OSi tBuMe 2] as precursors for MOCVD of hafnium silicate films

Hafnium β-diketonatochlorides HfCl 2(thd) 2 ( 1), HfCl(thd) 3 ( 2) as well as β-diketonato-silylamide and/or siloxide derivatives of 1 namely Hf(thd) 2[N(SiMe 3) 2] 2 ( 3), Hf(thd) 2(OSiMe 3) 2 ( 4) and Hf(thd) 2(OSi t BuMe 2) 2 ( 5) (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) were synthesized and characterized by elemental analysis, FT-IR, 1H NMR and TGA. 2 and 5 were also characterized by single-crystal X-ray diffraction. The siloxide ligands are in cis position for 5 and exert a strong trans effect. The new volatile compounds were tested as single-source precursors for the deposition of HfSi x O y films by pulsed liquid injection MOCVD on Si(1 0 0) and R plane sapphire. The as-deposited at 600–800 °C films were essentially amorphous, Hf-rich (Hf/Hf + Si = 0.7–0.85) and smooth.

Synthesis and characterization of hafnium tert-butylacetoacetate as new MOCVD precursor for HfO 2 films

A new hafnium β-ketoesterate Hf(tbob) 4 (tbob= tert-butyl-3-oxobutanoate or tert-butylacetoacetate) was obtained by ligand exchange reaction applied to Hf 2(O i Pr) 8( i PrOH) 2. It was characterized by elemental analysis, FT-IR, 1H NMR, mass-spectroscopy and TGA. The compound is volatile and it was tested for the growth of HfO 2 films on Si(100) and R-plane sapphire substrates at 600–800 °C by pulsed liquid injection MOCVD. The films were characterized by XRD, XPS and AFM. Stoichiometric amorphous films were obtained on silicon, while those on sapphire were relatively well crystallized (00l) monoclinic. The growth was kinetically limited in all the temperature range studied (600–800°C).

Growth Kinetics, Composition, and Morphology of Co3O4 Thin Films Prepared by Pulsed Liquid‐Injection MOCVD

AbstractCobalt oxide films were grown by pulsed liquid injection MOCVD using Co(thd)2 dissolved in monoglyme as the precursor. The structure, morphology, and growth rate of the layers deposited on silicon substrates were studied as a function of solution concentration, deposition temperature, and oxygen partial pressure. X‐ray diffraction (XRD) of films deposited from 350 °C to 540 °C showed a pure Co3O4 spinel structure and no CoO was detected, even at the lowest oxygen pressure. X‐ray photoelectron spectroscopy (XPS) was used to study the surface composition and oxidation states. Surprisingly, XPS spectra recorded for most of the films seemed to correspond to CoO. This unexpected oxidation state on the surface was assigned to the effect of the high density of edges and corners present in the surface morphology.

Pulsed liquid-injection MOCVD of high-K oxides for advanced semiconductor technologies

HfO 2 and SrTiO 3 films were grown on silicon by liquid injection metal organic chemical vapour deposition. The microstructure and structure of the films were characterised by X-ray and electron diffraction, X-ray reflectometry, infrared spectroscopy, and microscopy techniques. In both cases, we emphasised the role of precursors in the resulting composition and microstructure of the films. Dense films of HfO 2, either amorphous or crystalline depending on the deposition temperature, were synthesised using Hf(O t Bu) 2(mmp) 2 precursor. Permittivity values of 14–19 were obtained, consistent with the monoclinic structure determined from X-ray diffraction. Optimised films exhibit breakdown field of 6 MV cm −1 and leakage current densities as low as 10 −8 A cm −2 at 1 V. Polycrystalline SrTiO 3 films were grown using either a mixture of precursors or a heterometallic precursor. The heterometallic precursor provides some advantages such as a lowering of the crystallisation temperature of the perovskite-type phase and a reduction of carbonate impurities at low temperatures. It also allows to keep the films composition constant over a wide temperature range (550–750 °C). The films are highly textured with [ 0 0 1 ] SrTi O 3 parallel to [0 0 1] Si. The permittivity depends strongly on the films thickness ( ɛ r ∼ 30 for 10 nm and ɛ r ∼ 100 for 100 nm). An equivalent oxide thickness of 1.36 nm (for physical thickness of 15.0 nm) was obtained for optimised SrTiO 3 film, with a leakage current density of 10 −2 A cm −2 at 1 V.

Nucleation and growth of InN thin films using conventional and pulsed MOVPE

InN was deposited on c-sapphire and GaN substrates using conventional and pulsed metalorganic vapor-phase epitaxy. The nucleation and evolution of thin film growth was investigated. Growth temperature, V/III molar ratio, and substrate material were varied for the two different growth modes (conventional vs. pulsed MOCVD). It was found that InN deposition was sensitive to V/III molar ratio and growth temperature. Photoluminescence results show a peak emission at 0.83 eV. Results are presented that show the highest quality InN was deposited using pulsed metalorganic vapor-phase Epitaxy on GaN substrates.

Hafnium and zirconium tetramethylnonanedionates as new MOCVD precursors for oxide films

New bulky Zr and Hf β-diketonates (2,2,8,8-tetramethyl-4,6-nonanedionates, tmnd) were synthesized and characterized by elemental analyses, 1H NMR, FT-IR and mass spectrometry. A volatile copper compound Cu(tmnd) 2, an intermediate product of ligand synthesis, was isolated and characterized as well. The M(tmnd) 4 (M=Zr, Hf) compounds were tested as precursors for MOCVD of ZrO 2 and HfO 2 films. Preferentially (001)/(010)/(100) textured and in-plane oriented films of monoclinic oxides have been deposited by pulsed liquid injection MOCVD on R plane sapphire. Smooth films could be grown, especially on sapphire and at low temperature (500 °C). The films on Si(100) were polycrystalline and had rougher surface. XPS study showed 3–4 and 7–8 at.% of carbon in HfO 2 and ZrO 2 films, respectively. Zr(tmnd) 4 and Hf(tmnd) 4 lead to significantly higher growth rates of ZrO 2 and HfO 2 films at low temperature than conventional Zr(thd) 4 and Hf(thd) 4 precursors (thd=2,2,6,6-tetramethyl-3,5-heptanedionate) and are attractive precursors for oxide films.

Thick SmBCO layers and SmBCO/YBCO structures grown by pulsed injection MOCVD

Pulsed liquid injection MOCVD technique was applied for the growth of thin (∼0.5 μm) and thick (>2 μm) Sm 1+ x Ba 2− x Cu 3O 7− δ (SmBCO) layers and thick SmBCO/YBCO heterostructures on LaAlO 3(0 0 1) and on stainless steel (IBAD) substrates. Thin and thick SmBCO films as well as heterostructures were grown epitaxially on LaAlO 3 substrates. Critical temperature of SmBCO layers ( T c = 90–92 K, Δ T c = 1–2 K) was almost independent of Sm/Ba substitution ratio in the range of x = 0–0.2. Critical current density J c depended on film thickness with ∼3 MA/cm 2 at 77 K for 0.5 μm films and ∼0.6–0.8 MA/cm 2 for film thickness > 2 μm. We did not obtain the expected improvement of J c in SmBCO/YBCO heterostructures with respect to single YBCO or SmBCO layers. Thick SmBCO films on metallic IBAD substrates were c-axis textured and had preferential in-plane orientation (FWHM∼7°, J c ∼0.05 MA/cm 2 at 77 K).