Organometallic Chemical Vapor Deposition Research Articles

Multi-parameter process prediction with neural networks

Neural networks (NNs) are used to predict characteristics of GaAlAs layers grown by organometallic chemical vapor deposition (OMCVD). Traditional statistical techniques fail because there are many parameters which control the growth process and relatively few experiments to allow a full description of the effect of changing parameters. A successive approximation technique with NNs was developed which enables the most relevant input parameters to be selected first by a linear NN and then used by a more general NN to accurately predict the layer characteristics. In addition, by training to predict the correction to analytic approximations for the layer characteristics, maximum use is made of prior knowledge about the problem which results in a significant improvement in predictive capability beyond the simple analytic approximations.

Electrospray organometallic chemical vapor deposition—A novel technique for preparation of II–VI quantum dot composites

A novel technique combining electrospray and organometallic chemical vapor deposition (OMCVD) has been developed for the synthesis of new II–VI quantum dot composites. CdSe nanocrystals (quantum dots) of selected size are dispersed in a pyridine/acetonitrile mixture. The nanocrystals are transferred by electrospray into the growth zone of an OMCVD reactor and codeposited on a ZnSe matrix grown from hydrogen selenide and diethyl zinc. Composites consisting of CdSe nanocrystals and an amorphous or polycrystalline ZnSe matrix have been deposited on glass substrates at temperatures of 150–250 °C. Room-temperature absorption and photoluminescence spectra show optical transitions characteristic of the initial nanocrystal dispersions. The emission wavelength may be tuned in a broad spectral region by incorporating nanocrystals of varying sizes. The composites have been characterized by Auger electron spectroscopy, high resolution transmission electron microscopy, and scanning transmission electron microscopy.

Lead zirconate titanate thin films on ruthenium dioxide; in situ synthesis using organometallic chemical vapor deposition

Abstract In this paper the organometallic chemical vapor deposition (OMCVD) of RuO2 using the precursor ruthenocene, Ru(C5H5)2, will be discussed. Stoichiometric RuO2 thin films with a specific resistivity of about 50 μΩcm were obtained both on strontium titanate and platinized silicon wafers at temperatures between 300–700°C. PbZr0.8Ti0.2O3 thin films were in situ deposited onto these RuO2 electrodes. The ferroelectric behavior of the films obtained on the RuO2 electrodes is compared with those obtained on platinum electrodes. Attempts to deposit in-situ a RuO2 top electrode on the PbZr0.8Ti0.2O3 were unsuccessful.

Organometallic chemical vapor deposition of rare earth oxide thin films. Application for steel protection against high temperature oxidation

In this paper, an OMCVD method is used for local introduction of rare earth elements at chromia former alloy surfaces. Effect of such coatings on high temperature oxidation of two common stainless steels (AISI 304 and F17Ti) are comparatively tested in isothermal and cyclic conditions. In both cases, and particularly under cyclic conditions, a significant improvement of the high temperature behaviour is observed, depending on the rare earth element used for coating.

Ferroelectric properties and fatigue of PbZr0.51Ti0.49O3 thin films of varying thickness: Blocking layer model

Ferroelectric capacitors having Pt bottom and top electrodes and a ferroelectric film of composition PbZr0.51Ti0.49O3 (PZT) were fabricated and investigated. The PZT films of thicknesses varying from 0.12 to 0.69 μm were prepared by organometallic chemical-vapor deposition. Annealed capacitors were investigated by capacitance, hysteresis, and pulse switching measurements. It is found that the thickness dependence of the reciprocal capacitance, the coercive voltage, and the polarization measured by pulse switching can all be explained by a blocking layer model, in which a dielectric layer of thickness dbl and relative permittivity εbl is situated between the PZT film and an electrode. It is shown that (i) the coercive field is independent of thickness having a value of 2.4 V/μm; (ii) the ratio εbl/dbl is in the range 20–28 nm−1; (iii) the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 V m2/C; and (iv) the polarization depends on the electric field in the PZT layer, independent of thickness. Pulse switching endurance measurements showed that in the saturation range the fatigue for these ferroelectric capacitors is determined by the pulse voltage and is independent of the thickness.

Measurement of piezoelectric coefficients of ferroelectric thin films

This article presents measurements of piezoelectric coefficients of lead zirconate titanate (PZT) thin films. The normal load method is used to measure the coefficients for PZT films with various compositions prepared by the sol-gel technique or by organometallic chemical vapor deposition (OMCVD). The as-deposited OMCVD films have a piezoelectric coefficient of 20–40×10−12 m/V, whereas the unpoled sol-gel films are not piezoelectric. After poling the thin films having a composition near the morphotropic phase boundary; these values increase to 200×10−12 m/V for OMCVD films and 400×10−12 m/V for sol-gel films. The difference may arise from an incomplete poling of the OMCVD films.

Reduction of zinc diffusion into the collector of InP-based double heterojunction bipolar transistors grown by organometallic chemical vapor deposition

It is shown that the growth of emitter layers of InP/InGaAs/InP double heterojunction bipolar transistors can result in significant Zn diffusion from the base into the collector, with the extent of diffusion depending on the n-doping level of the emitter. This behavior is explained in terms of nonequilibrium point defects induced by a combination of surface pinning of the Fermi level and n doping. It is also shown that the Zn diffusion can be substantially reduced by using AlInAs, instead of InP, as the emitter layer. The difference in behavior is shown to be at least in part due to the lower diffusivity of group III interstitials in AlInAs. Furthermore, it is shown that the introduction of only 50 nm of AlInAs between the n-InP emitter and p+-InGaAs base resulted in a significant reduction of Zn diffusion into the collector.

Nitrogen-doped ZnSe with selenium-rich growth by low-pressure organometallic chemical vapor deposition

A high-quality nitrogen-doped p-type ZnSe epilayer on (100) GaAs substrate was obtained under selenium-rich growth conditions by low-pressure organometallic chemical vapor deposition. Ammonia was used as the dopant source. The resistivity (0.5 Ω cm) and the free-carrier concentration (p=8.8×1017 cm−3) of as-grown ZnSe:N were derived from Hall measurements. With selenium-rich growth conditions, we can reduce the concentration of compensation defects (VSe-Zn-NSe which acts as a donor in ZnSe). Nitrogen is found to incorporate in ZnSe as a shallow level, which is examined by the dependence of free-to-acceptor emission on the NH3/H2Se molar ratio. The carrier concentration of as-grown ZnSe:N seems to change insignificantly within a wide range of growth temperatures. That is thought to be useful for device fabrication due to uniformity considerations.

Use of Tetraneopentylchromium as a Precursor for the Organometallic Chemical Vapor Deposition of Chromium Carbide: A Reinvestigation

Thin films of chromium carbide have been grown by organometallic chemical vapor deposition (OMCVD) from tetraneopentylchromium (Cr[CH[sub 2]C(CH[sub 3])[sub 3]][sub 4], CrNp[sub 4]). Deposition was performed in a hot wall, low pressure reactor at 520 and 570[degrees]C and a pressure of 1.33 [times] 10[sup [minus]2] Pa (10[sup [minus]4] Torr). No carrier gas was used. The resulting films were characterized by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction (XRD), scanning electron microscopy (SEM), and elastic recoil detection (ERD). These data show that the films are of high quality, with very low oxygen content, and contain some residual amorphous carbon. Films grown at 570[degrees]C are crystalline. The observed crystalline phase is Cr[sub 7]C[sub 3]. 13 refs., 7 figs., 1 tab.

Molecular routes to cobalt arsenide and cobalt phosphide thin films. Comparison of a two-source and a single-source chemical vapour deposition

Cobalt arsenide and phosphide thin films were prepared by organometallic chemical vapour deposition (OMCVD) at deposition temperatures between 300 and 500°C in a hot-wall reactor using a two-source method and a single-source method. The combination of tricarbonylnitrosylcobalt (-I) and di- t-butylphosphine or di- t-butylarsine was employed as a two-source method. The known hexacarbonyldicobalt clusters, CO 2 (CO) 6(μ-E 2) (E = P, As), and the substituted dicarbonylnitrosylcobalt complexes, Co(CO) 2 [E( tBu) 2H](NO) (E = P, As), were used as a single source precursors. Auger electron spectroscopy indicated that the Co : P and Co : As ratios in most of the films were near unity with only a small amount of impurities such as carbon and oxygen. Electrical resistivity of the films at room temperature ranged from 450 to 1140 μΩ-cm for cobalt phosphide and 115 to 1140 μΩ-cm for cobalt arsenide. X-ray diffraction analysis revealed that cobalt arsenide films were polycrystalline, whereas cobalt phosphide films ranged from amorphous to polycrystalline. The grain size of the films ranged from 150 to 2000 Å measured by field-emission scanning electron microscopy. The film growth rate ranged from 4 to 30 Å min −1, for the single source methods and 150 to 330 Å min −1, for the two-source methods.

Magneto-optics of quantum wires grown on V-grooved substrates

AlGaAs/GaAs undoped quantum wires (QWRs) grown by organometallic chemical vapour deposition on V-grooved substrates have been studied by photoluminescence (PL) and photoluminescence excitation (PLE) in zero and finite magnetic fields. From the study of the diamagnetic shift of the peaks as a function of wire width and orientation with respect to the magnetic field, we have deduced one-dimensional effective masses for the lowest subband transitions.

Characterization of Al-doped n-type ZnSe prepared under a zinc-rich growth condition by low-pressure organometallic chemical vapor deposition

High conductivity n-type ZnSe with ϱ = 0.01 ωcm and n = 2.4 × 10 18 cm −3 is obtained on (100) GaAs substrates by low pressure organometallic chemical vapor deposition. The 14 meV full width at half maximum of the 77 K photoluminescence near-band-edge emission shows a high quality of as-grown Al-doped ZnSe epilayers. With a suitable Al doping level, a strong photoluminescence intensity of near-band-edge emission is obtained. The behavior of near-band-edge emission and of self-activated emission related to the incorporation of aluminum are discussed in this paper.

Organometallic chemical vapor deposition and characterization of indium phosphide nanocrystals in Vycor porous glass

Indium phosphide has been deposited in 40 and 150 Å Vycor porous glass by the reaction of trimethylindium with excess PH3. X-ray diffraction (XRD) of the red, transparent samples confirms the presence of crystalline indium phosphide. The amount of III-V material deposited within the glass matrix (loading) and annealing conditions influence the crystallinity and particle size of the nanocrystallites. The absorption spectra of vacuum-annealed samples is blue shifted with respect to bulk InP, with maxima ranging from 500 to 700 nm for both the 40 and 150 Å samples and is consistent with size quantization. The nonlinear optical properties of these nanocrystallite composites have been evaluated by Z-scan measurements and are characterized by a defocusing refractive nonlinearity influenced by a substantial nonlinear loss presumed to be caused by two-photon absorption.

Structure of (001) GaAs surfaces during epitaxial growth by organometallic chemical vapor deposition

Under typical atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) growth conditions with trimethylgallium (TMG) and arsine sources, reflectance-difference (RD) spectra show that the (001) GaAs surface is in the d(4×4)-like state. With sufficiently high TMG and low AsH3 exposures, we observe RD spectra similar to those obtained during atomic layer epitaxy (ALE) at lower temperatures.

Preparation of ZnO Films by Low-pressure Organometallic Chemical Vapor Deposition

Abstract Using zinc acetate as a precursor, ZnO films have been prepared on sapphire () substrates at pressures of 2.7 × 10−2 and 6.7 × 10−3 Pa. The deposition rate increased with substrate temperature. The crystal structure of ZnO film was dependent on the substrate temperature and H2O partial pressure. In particular, oriented () ZnO films have been formed at 350 °C at 2.7 × 10−2 Pa.

Growth of ZnO films by low-pressure organometallic chemical vapor deposition

Using zinc acetate as a precursor, ZnO films have been prepared on sapphire (1 1 02) at 270 °C at an H 2O partial pressure of 6.7 x 10 −2 Pa. Oriented (11 2 0) ZnO films are formed at a sublimation rate of zinc acetate below 2.85 mg h −1. Intense absorption is observed for these ZnO films at wavelengths <380 nm, corresponding to the band gap of ZnO.

Particle contamination in low pressure organometallic chemical vapor deposition reactors: Methods of particle detection and causes of particle formation using a liquid alane (AlH3) precursor

Two methods of analyzing particles were interfaced to a low pressure chemical vapor deposition reactor used to deposit Al films from the liquid precursor dimethylethylamine alane. A laser light scattering particle counter was used to monitor particles (≳200 nm) in real time and established that the appearance of particles corresponded to the flow of precursor into the reactor. A particle impaction system was used to collect particles (≳20 nm) for analysis using analytical transmission electron microscopy and electron diffraction. Typical sizes of the Al particles were in the range 20–1000 nm. Purposely introducing trace amounts of H2O, CO, and O2 into the reactor during the flow of the precursor caused an increase in the number of particles. Our results suggested that Al particle formation was induced by impurities in the gas phase (particularly H2O) although competing mechanisms could not be ruled out.

Organometallics-chemical vapor deposition: A new technique for the preparation of non-acidic, zeolitesupported Pd and Pt catalysts

The OM-CVD (Organometallic Chemical Vapor Deposition) technique has been applied to the preparation of zeolite-supported Pd and Pt catalysts for hydrocarbon conversion. This has been achieved via a two step process; the organometallic precursor is first deposited inside zeolite cages and then decomposed under controlled reduction conditions to metal particles.

New developments in spectroellipsometry: the challenge of surfaces

Advances in technology, especially semiconductor technology, are providing new opportunities for the development and application of spectroellipsometry and related techniques, particularly for real-time diagnostics and control. Two recent examples of surface and near-surface analysis illustrate possibilities. Reflectance-difference spectroscopy of (001) GaAs growth surfaces under ultra-high vacuum and atmospheric-pressure conditions has provided the first evidence of dimer formation during organometallic chemical vapor deposition (OMCVD). Kinetic-ellipsometric determination of the composition x of Al x Ga 1− x As alloys during chemical beam epitaxy (CBE), with x established by a history-independent, minimal-data approach, has been used to realize the first fully automatic closed-loop feedback system for controlling growth directly. Possible future directions are discussed.

Surface reconstruction of GaAs (001) during OMCVD growth

Surface reconstruction of GaAs (001) during organometallic chemical vapour deposition (OMCVD) growth has been investigated with reflectance-difference spectroscopy (RDS). RD spectra reveal that surface reconstructions similar or identical to (4 x 2), (2 x 4), and c (4 x 4) that occur on surface prepared by molecular beam epitaxy (MBE) in ultrahigh vacuum (UHV) occur even in atmospheric pressure OMCVD growth environments. Based on the RDS database we established on static surfaces in UHV , we studied the structure of surfaces under both static and dynamic conditions in non-UHV ambients. We find, in contrast to previous models, that the surfaces under various non-UHV conditions exhibit dimer formation. In addition, OMCVD growth and atomic layer epitaxy (ALE) typically occur under disordered c (4 x 4)[ d (4 x 4)]-like conditions where the surface is terminated by multilayers of As. When trimethylgallium (TMG) and arsine (AsH 3 ) are supplied simultaneously, the surface structure varies as a function of the supply rates of TMG and AsH 3 , and the substrate temperature.