Metallo-organic Chemical Vapour Deposition Research Articles

Tungsten nitride thin films prepared by MOCVD

Polycrystalline tungsten nitride thin films were grown by low pressure metallo-organic chemical vapor deposition (MOCVD) using (tBuN)2W(NHtBu)2 as the single-source precursor. Deposition of uniform thin films on glass and silicon substrates was carried out at temperatures 723–923 K in a cold-wall reactor, while the precursor was vaporized at 333–363 K. The growth rates were 2–10 nm/min depending on the condition employed. Bulk elemental composition of the thin films, studied by wavelength dispersive spectroscopy (WDS), is best described as WNx (x = 0.7–1.8). The N/W ratio decreased with increasing temperature of deposition. X-ray diffraction (XRD) studies showed that the films have cubic structures with the lattice parameter a = 0.414–0.418 nm. The lattice parameter decreased with decreasing N/W ratio. Stoichiometric WN thin films showed an average lattice parameter a of 0.4154 nm. X-ray photoelectron spectroscopy (XPS) showed that binding energies of the W4f7/2, W4f5/2, and N1s electrons were 33.0, 35.0, and 397.3 eV, respectively. Elemental distribution within the films, studied by secondary ion mass spectroscopy (SIMS) and Auger spectroscopy depth profilings, was uniform. The SIMS depth profiling also indicated that C and O concentrations were low in the film. Volatile products trapped at 77 K were analyzed by gas chromatography–mass spectroscopy (GC–MS) and nuclear magnetic resonance (NMR). Isobutylene, acetonitrile, hydrogen cyanide, and ammonia were detected in the condensable mixtures. Possible reaction pathways were proposed to speculate the origin of these molecules.

Characterization of the crystallographic defect structure in selected-area epitaxial growth of GaInAs on InP by metallo-organic chemical vapour deposition

We describe the chemical and crystallographic structure of selected-area metallo-organic chemical vapour deposition overgrowths of InP and GaInAs on partially masked (100) InP substrates, using energy-dispersive X-ray analysis, transmission electron microscopy and high resolution electron microscopy. The presence of the oxide mask, which specifies the selected areas for epitaxial deposition, has the effect of perturbing the gas flow over the wafer surface, which can induce a modification of the local composition and morphology of the depositing material and result in the incorporation of interfacial misfit stresses. High densities of interfacial misfit dislocations are observed in material in which this perturbation is greatest. The majority of the dislocations in the planar epitaxial regions have a 60° character, but in the highly mismatched and facetted regions of growth adjacent to the mask edges, a variety of novel misfit-relieving dislocation structures are observed and these are identified by high resolution electron microscopy.

Structural studies of some Group 12 metal alkyl adducts: the X-ray crystal structures of Me 2Zn[Me 2N(CH 2) 2NMe 2], Me 2Cd[Me 2N(CH 2) 2NMe 2], (Me 3CCH 2) 2Zn[Me 2N(CH 2) 2NMe 2] and (Me 3CCH 2) 2Cd[Me 2N(CH 2) 2NMe 2

The X-ray crystal structures of a series of group 12 metal alkyl adducts Me 2M[Me 2N(CH 2) 2NMe 2] {M  Zn ( 1), Cd ( 2)} and (Me 3CCH 2) 2M[Me 2N(CH 2) 2NMe 2] {M  Zn ( 3), Cd ( 4)} have been determined. Each adduct exists as a mononuclear, molecular unit with pseudo-tetrahedral coordination at the metal centre. Compound 1 crystallizes in space group P2 1 / a, a 13.868(3), b = 11.616(2) and c = 7.588(2) Å, β = 94.83(2)°, compound 2 in space group Cmca, a = 11.196(2), b = 12.179(2) and c 17.969(3) Å. Compounds 3 and 4 are isostructural in space group C2 / c with the following unit cell dimensions for Zn {Cd}: a = 17.167(5) {17.604(5)}, b = 9.369(3) {9.484(3)}, and c = 12.916(3) {12.758(3)} Å, β = 107.83(2) {106.07(2)}.° Compound 1 and the parent alkyl of 4 have been used successfully in the growth of thin films by metalloorganic chemical vapour deposition, 1 as a dopant in the growth of p-type GaAs, and [Me 3CCH 2] 2Cd as a Group 12 source in the growth of CdS.

Optimizing metallo-organic chemical vapour deposition of YBCO films: substrates and [formula omitted] conditions

The results of a study of YBCO thin films prepared by metallo-organic chemical vapour deposition on different substrates, including Al 2O 3, MgO, ZrO 2(Y 2O 3), NdGaO 3, SrTiO 3 and LaAlO 3 are presented. The critical current density correlates with the lattice mismatch between the film and the substrate. A maximum j c value was achieved on LaAlO 3 i.e. 1.6 × 10 7 A cm −2 (4.2 K, H = O T) . The sharp maxima of j c was observed for the film on MgO and ZrO 2 (Y 2O 3) at a deposition temperature of 840–850°C and P o 2 of 7 Torr.

CdTe rotation growth on silicon substrates by metallo-organic chemical vapour deposition

We observed a 30° in-plane rotation slip for (111) CdTe epilayers grown on (111) Si substrates by metallo-organic chemical vapour deposition when we increased the group VI to II ratio. We define this effect as rotation growth. This rotation alignment reduces the lattice mismatch between CdTe and silicon from 19% to 3.4%, thus promising better crystallinity. When the group VI to II ratio is increased, the full width at half-maximum of the X-ray rocking curve is decreased from over 1000″ to 400″ for an epilayer 1 μm thick. The rotation growth mechanism was examined by Auger electron spectroscopy and results show that the tellurium atoms are adsorbed to the silicon surface more readily than are cadmium atoms. We also found that the (111) Si substrate had to be misoriented toward the [110] direction to suppress twinning in CdTe rotation growth.

Effect of the [formula omitted] orientations and polarities of GaAs substrates CdTe buffer layer structural properties

CdTe layers were grown by metallo-organic chemical vapour deposition on GaAs substrates of different ( {h11}) orientations and polarities. The morphology and structural properties of the epilayers were investigated using several techniques, namely scanning electron microscopy, transmission electron microscopy and double crystal X-ray diffraction. The best results were obtained for epitaxy on (211) A and (311) B substrate orientations. The occurrence of twinning in the cases of opposite polarity, i.e. (211) B and (311) A, was attributed to the presence of single dangling bonds on the etched substrate surfaces.

Growth of high quality ZnSe epitaxial layers on transparent substrates CaF 2 by atmospheric pressure metallo-organic chemical vapour deposition

High quality ZnSe epitaxial layers (epilayers) on CaF 2(111) transparent substrate have been successfully fabricated for the first time by atmospheric pressure metallo-organic chemical vapour deposition, using dimethylzinc and H 2Se as sources. The double-crystal X-ray diffraction pattern (111) shows a little shift of ZnSe diffraction peak towards a small diffraction angle, and the full width at half-maximum of the diffraction peak value from its (111) face is about 0.20°. The optical and electrical characteristics of ZnSe epilayers were measured by photoluminescence, scanning electron microscopy and the Van Der Pauw method; the epilayers exhibit a high crystallographic quality and reveal an even mirror surface. All epilayers have high resistivities of up to 10 7 Ω cm. From the analyses on the energy shift of the luminescence line, a compressive stress has been found in the epilayer sides of these heterostructures. This is consistent with the stresses predicted for a lattice between mismatch the ZnSe epilayer and the CaF 2 substrate.

Chemical vapour deposition of metals and metal silicides on the internal surfaces of porous silicon

Cobalt, cobalt monosilicide and rhenium thin films have been deposited on the internal walls of both n- and p-type porous silicon (PS) by metallo-organic chemical vapour deposition (MOCVD) at moderate temperatures and low pressure. Characterisation of the films by Rutherford Back-Scattering (RBS) showed penetration of Co, CoSi and Re into the pores to a depth of at least 2 μm, the concentration decreasing with increasing depth; NRA light element analysis revealed that substantial levels of oxygen and, to a lesser extent, carbon were present in the films.

Heteroepitaxy of TiO 2, VO 2 films and TiO 2/VO 2 multilayers grown on sapphire (11 [formula omitted]0) by metallo-organic chemical vapor deposition

Single-crystal TiO 2 and VO 2 films in single-layer and multilayer configurations have been successfully grown on sapphire (11 2 0) by the metallo-organic chemical vapor deposition technique. The epitaxial orientation relationships were determined by the X-ray diffraction and transmission electron microscopy techniques. High resolution electron microscopy studies were performed to examine the microstructures of the films at atomic level.

Study of defects and interfaces on the atomic scale in epitaxial tio2thin films on sapphire

Abstract TiO2 thin films grown on (11 0) sapphire (α-Al2O3) at 800°C by the metallo-organic chemical vapour deposition technique have been characterized by transmission electron microscopy. The TiO2 thin films are single-crystal rutile. The epitaxial orientation relationship between the rutile thin films (R) and the sapphire substrates (S) is (101)[010]R‖(110)[0001]s. Growth twins are commonly observed in the films with (101) twin planes and twinning directions. The atomic structure of twin boundaries and TiO2-α-Al2O3 interfaces have been investigated by high-resolution electron microscopy. When the interfaces are viewed in the direction of [010]R-[0001]s, the interfaces appear structurally coherent along the direction of [10]R-[100]s. The small misfit (0.5%) is accommodated at interface steps. In contrast, in the direction of [10]R-[100]s, the interfaces are semicoherent. Growth mechanisms are discussed, based on information about the atomic structure of the interfaces.

Plasma-assisted chemical vapour deposition of hard coatings with metallo-organic compounds

In this work the use of two metallo-organic compounds, titanium tetrakisdialkylamides, was investigated with a pulsed d.c. plasma-assisted chemical vapour deposition process to deposit layers on steel substrates and hard metals. The layers have been studied by scanning electron microscopy X-ray diffraction and wavelength-dispersive X-ray analysis. It is shown that chlorine-free titanium carbonitride coatings can be obtained by metallo-organic chemical vapour deposition even at substrate temperatures of lower than 450°C.

Residual stresses analyses of metallo-organic chemically vapour-deposited Cr 7C 3 coatings on SAE 4135 steel substrates

Chromium carbide coatings have been prepared by metallo-organic chemical vapour deposition in a hot-wall reactor using Di Cumene chromium as precursor. Films were deposited on SAE 4135 steel substrates in the temperature range 300–550 °C. A buffer layer of amorphous chromium carbide was deposited at a low temperature to improve the adhesion of the coatings. Coatings have been characterized by scanning electron microscopy, X-ray diffraction, electron probe microanalysis, X-ray photoelectron spectroscopy and secondary-ion mass spectrometry. A thin iron oxide phase (Fe 3O 4) was found at the layer-substrate interface. The crystalline films deposited at 510 °C exhibit strong internal compressive stresses whereas tensile stresses were found in the substrate. Three of these samples have been submitted to bending experiments with a view to activating the deformation mechanism which would tend to relax partially or totally the internal stresses by an interfacial or volume crack opening. The variation in the internal stresses measured by the X-ray method has been studied with the bending experiment.

Recent developments in thin film solar cells

In recent years, remarkable progress has been made in improving the photovoltaic (PV) conversion efficiencies of thin film solar cells. The best active-area efficiencies (air mass 1.5) of thin film solar cells reported are as follows: polycrystalline CuInSe 2, 14.1%; CuIn(Ga)Se 2, 12.9%; CdTe, 12.3%, total area; single-junction hydrogenated amorphous silicon (a-Si:H), 12.0%; multiple-junction a-Si:H, 13.3%; cleaved epitaxial GaAsGa 1− x Al x As, 21.5%, total area. Laboratory methods for preparing small thin film solar cells are evaporation, closed-space sublimation, closed-space vapor transport, vapor phase epitaxy and metallo-organic chemical vapor deposition, while economic large-area deposition techniques such as sputtering, glow discharge reduction, electrodeposition, spraying and screen printing are being used for module fabrication. The following aperture-area efficiencies have been measured, at the Solar Energy Research Institute, for thin film modules: a-Si:H, 9.8%, 933 cm 2; CuIn(Ga)Se 2, 11.1%, 938 cm 2; CdTe, 7.3%, 838 cm 2. The instability issue of a-Si:H continues to be a high priority area. It is necessary to improved the open-circuit voltage of CuIn(Ga)Se 2 cells, which do not seem to exhibit any intrinsic degradation mechanisms. With continued progress and increased production, PV modules are likely to become competitive for medium-scale power requirements in the mid-1990s.

On the use of basic zinc acetate Zn 4O(CH 3CO 2) 6 as a novel precursor for the deposition of ZnO by low-pressure metallo organic chemical vapour deposition: their characterization by low energy electron induced X-ray emission spectroscopy

On the use of basic zinc acetate Zn 4O(CH 3CO 2) 6 as a novel precursor for the deposition of ZnO by low-pressure metallo organic chemical vapour deposition: their characterization by low energy electron induced X-ray emission spectroscopy

Uniformity of an embedded stripe large optical-cavity GaAs/GaAlAs double-heterostructure laser grown by metallo-organic chemical vapor deposition

Large optical-cavity GaAs/GaAlAs double-heterostructure stripe geometry laser with laterally effective step change of the refractive index is described. The stabilization of the transverse mode is achieved by regrowing an embedded stripe selectively on a large optical cavity, using metallo-organic chemical vapor deposition. The near-field and the far-field patterns confirm the index guiding mechanism of the light. No kinks were observed in the light versus current characteristics up to light power of 200 mW/facet. The threshold current uniformity is comparable to those of gain-guided lasers grown by metallo-organic chemical vapor deposition.

Semiconductors: Photochemical processing

The formation of thin layers of inorganic materials on semiconductor surfaces by the photo initiated decomposition of organometallic compounds is a technique that is receiving increasing attention. Deposition of these layers by heating (pyrolysing) such compounds has become a standard technology, and has acquired the acronym mocvd (metallo-organic chemical vapour deposition).

A study of zinc doping in metallo-organic chemical vapor deposition of InP

Zn-doped InP epitaxial layers, grown by atmospheric pressure metallo-organic chemical vapor deposition using the adduct process, have been characterized by Hall effect, secondary ion mass spectroscopy, and electrochemical profilling techniques. From the results of these measurements the dopant vapor concentration dependence of the room temperature carrier density, net acceptor density, and total Zn atomic density in the layers has been ascertained and the activation energy of the main acceptor level has been measured as 30 meV. A novel technique for measuring the extent of dopant diffusion is described and this has been used to determine diffusion coefficients of Zn of 1–6×10−13 cm2 s−1, values which are much lower than those previously reported. p-n homojunction devices have also been fabricated and these were evaluated by I-V and C-V measurements. The classical diode equation was obeyed over large ranges of current, and ideality factors for the diodes were found to be 1.2–1.5. These results, together with the C-V measurements, show that high quality InP homojunctions can be produced by the adduct technique and the successful use of the material in advanced devices indicates that this is a valuable process for the future.