Photo-assisted growth of ZnTe by metalorganic chemical vapour deposition

The metalorganic chemical vapour deposition (MOCVD) photo-assisted growth of ZnTe using a xenon lamp has been performed at atmospheric pressure under hydrogen as a carrier gas. Epitaxial growth was achieved on (100) GaAs, (100) GaSb and (100) ZnTe substrates with diethylzinc (DEZn) and diethyltellurium (DETe) as precursors. We have studied the growth rate as a function of the growth temperature, the partial pressure of precursors, the inlet partial pressure ratio R = VI/II, the light intensity and the energy of the irradiating photons. A growth rate enhancement has been observed for illuminated layers grown on GaAs and ZnTe substrates in comparison with those grown without illumination. We have not observed any measurable enhancement for layers grown onto (100) GaSb. The growth rate as a function of the light intensity increases for intensities higher than 20 mW / cm² and saturates for P > 120 mW / cm². We relate the growth rate enhancement to irradiating photons with an energy higher than the band gap of ZnTe at the growth temperature.     

Microstructure of hydrogenated silicon carbide thin films prepared by chemical vapour deposition techniques

We present the results of investigations on a variety of stoichiometric μc-SiC:H films deposited by Hot-Wire- and Plasma-Enhanced Chemical Vapour Deposition using monomethylsilane diluted in hydrogen as precursor gas. Infrared spectroscopy, grazing incidence X-ray diffraction, and Transmission Electron Microscopy were applied and compared to separate the contributions from the different structure phases of the material. It is shown that an evaluation of the crystalline volume fraction from the infrared absorption lineshape of the Si–C stretching mode is not possible, although stated in the literature. A correlation of this lineshape with the material strain is proposed. Moreover, a variation in strain, grain size, and structural defects is found depending on the deposition conditions, but a mixture of an amorphous and a crystalline phase could not unambiguously be identified.     

Chemical and plasmachemical vapour deposition of aluminium nitride layers

AIN was deposited pyrolytically by means of the aluminium trichloride-ammonia process (either introducing both compounds seperately or in complex form) and by plasmachemical reaction of aluminium trichloride with nitrogen at temperatures from 600 to 1300°C. Layers deposited onto (100) spinel had an epitaxial (0001) orientation, whereas fibre textures resulted on silicon and quartz glass.     

Paramagnetic defects in diamond films synthesized by the hot filament chemical vapour deposition

Defects in nitrogen‐doped diamond films, produced by hot filament chemical vapour deposition have been studied by Electron Spin Resonance (ESR), Raman spectroscopy and Scanning Electron Microscopy (SEM). The peak‐to‐peak ESR line width (ΔH _pp) varies in the range 0.36‐0.52 mT and depends on the nitrogen concentration in the process gas. In the case of nitrogen‐doped diamond films ESR spectrum shows a hyperfine structure typical of N_S⁰ paramagnetic centre. The shape of the central ESR line shows that it is a superposition of two components: a narrower Lorentzian and a broader Gaussian one, characterized by different saturation behaviour. With increasing nitrogen concentration in process gas the ratio of integral intensities A _G/A _L (Gausian to Lorentzian) of ESR spectrum also increases. The Raman spectra show that with increasing doping level the diamond Raman line at 1332.5 cm^‐1 broadens, the broad band at about 1530 cm^‐1 becomes more pronounced what indicate on degradation of diamond crystallinity and it is in agreement with SEM observation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Equilibrium and kinetics in the chemical vapour deposition of silicon

In the growth of silicon layers on various substrates it appears that the growth rate is not uniquely determined by substrate temperature and input parameters of the gases used. An analysis of this situation is given and essential points in the chain reaction of steps in the growth process will be indicated. Differences in growth rate reported for different experimental situations can be explained on the basis of this analysis where the temperature gradient normal to the growing interface will appear to be of special importance. Some examples are given of resulting surface morphology as a function of growth and etch conditions. Another point of interest in the growth process is the incorporation of dopant which determines the electrical properties of the layers. Here also equilibrium and kinetics show an interplay. For low growth rates there appears to be a good correlation between the concentration of impurities in the solid and the partial pressure of dopant in the gas phase. For growth rates exceeding a critical-value kinetic effects can be expected as those found in liquid phase epitaxy. It appears that an n-type dopant as phosphorus shows this effect. In this case the surface concentration of ionized donors exceeds the bulk concentration of these centres and trapping occurs at higher growth rates.     

Growth of bulk InGaN films and quantum wells by atmospheric pressure metalorganic chemical vapour deposition

InGaN bulk layers and single quantum wells were grown on 1.4 to 2.4 μm thick GaN on sapphire films by atmospheric pressure metalorganic chemical vapour deposition (AP-MOCVD). The morphology of the epitaxial layers was strongly affected by the V/III ratio in the gas phase. The incorporation efficiency of indium was observed to increase with higher growth rates and decreasing temperature, but was independent of the V/III ratio in the investigated parameter range. In_0.16Ga_0.84N single quantum wells showed intense quantum well related luminescence at room temperature, with a full width at half maximum of 7.9 nm at a thickness of 50 Å. Single quantum wells embedded in InGaN of graded composition showed superior properties compared to quantum wells with In_0.04Ga_0.94N barriers of constant composition.     

Preparation of extremely pure silver iodide

A method based on the direct interaction of crystalline silver and iodine at a temperature higher than the AgI melting point as well as a suitable apparatus permitting the obtaining of a granular product have been developed. Spectral analysis of 9 elements shows impurities content lower than 0.05 ppm. Two crystalline modifications – cubic (about 20%) and hexagonal (about 80%) are detected by X-ray analysis.     

The incorporation of oxygen impurities in semiconductor silicon in chemical vapour deposition

The incorporation of oxygen traces in chemical vapour deposited semiconductor silicon has been calculated for the temperature range of 1200–1500 K in dependence on the excess of hydrogen in the reaction gas. The results obtained correspond to the experimental data. With increasing temperatures of deposition and increasing excess of hydrogen the incorporation of oxygen decreases at a constant concentration of oxygen in the initial state.     

Impact of the gas flow ratio on the physical properties of GaN grown by vertical flow metalorganic chemical vapour deposition

We studied the effect of gas flow ratio of the H₂ carrier gas to the NH₃ precursor on the physical and crystal properties of GaN. GaN was grown by vertical reactor metalorganic chemical vapour deposition (MOCVD) on a low-temperature-deposited GaN buffer layer. A (0 0 0 1) sapphire substrate was used. The impact of the gas flow ratio as it was varied from 0.25 to 1 was investigated and discussed. With increase in flow ratio, the concentrations of magnesium and carbon impurities in GaN increased. The flow ratio of 0.5 is the optimum value to minimise the background electron concentration and to maintain crystal quality. The decrease in the background electron concentration is due to the compensation mechanism of acceptor-like magnesium and carbon impurities.     

Total pressure dependence of doping element incorporation during the chemical vapour deposition of epitaxial silicon

Starting from the literature on doping element incorporation at atmospheric and lower pressures the partial pressure of the dopants available within the deposition system is selected as a uniform basis of reference for the total pressure dependence of the doping element incorporation. It is shown that also at reduced pressures the incorporation equilibria of phosphor and arsenic, the author previously derived from the temperature dependence of the doping element incorporation may be used.     

Preparation and study of extremely pure naf single crystals

The authors employed various physical and chemical methods for the purification of NaF. The efficiency of these methods was controlled by absorption measurements and chemical analysis. From purified material a single crystal was grown in every case, the absorption of which was measured by a vacuum ultraviolet spectrophotometer in the far UV wavelength range. The absorption at 142 nm was found to be indicative of the presence of several transition and heavy metal ions. The effect of doping with several alkaline and alkaline earth ions and furthermore with Cl⁻ and OH⁻ ions on these spectra is discussed. It is shown that certain chemical methods used for purification introduce Cl⁻ ions into the material which are detectable by UV-spectrophotometry.     

Deposition of iron nanoparticles onto multiwalled carbon nanotubes by helicon plasma-enhanced,chemical vapor deposition

We report helicon plasma-enhanced, chemical vapor deposition (helicon-PECVD) of iron (Fe) nanoparticles onto multiwalled carbon nanotubes (MWCNTs) with ferrocene as an iron source. Ferrocene was evaporated from the bubbler by heating, and the helicon plasma treatment was performed with the evaporated ferrocene and hydrogen gas at (−)DC bias voltage. The resulting MWCNT/Fe nanoparticle hybrids were characterized by X-ray fluorescence spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and superconducting quantum interference device magnetometry.     

Reactor problems in modified chemical vapour deposition (i). the collapse of quartz glass tubes

In the case of the so-called “Modified Chemical Vapour Deposition” for the preparation of optical fiber preforms, the quartz glass reactor is identical with the substrate. Therefore, the knowledge of reactor properties such as the viscous flow of the tubes (collapse) and the heat transport through the wall are especially important for a successful control of the process. As a first step, an analysis is presented for the calculation of the viscous flow of the tubes under the real conditions of dynamic heating by a traversing flame. The experimental determination of the material parameters surface tension and viscosity by collapsing experiments yields an approach to the problem of the temperature distribution in the tube wall.     

Photoelectron spectroscopic and thermodynamic studies of the formation of iron boride layers on pure iron substrates in powder boriding

In-situ studies of chemical reactions and transport processes occurring in powderous rection media during the production of refractory layers on metallic substrates are impossible. However, results of the studies of the layers formed by means of suitable surface analyses, e.g. ESCA, combined with thermodynamic estimations permit these processes to be deduced. Element distribution and bonding states in the boundary region of the surface as determined from the photoelectron spectra of powder-borided high grade iron samples correlate with the occurrence of thermodynamically possible gaseous intermediate compounds which may be formed from the components of a certain boriding powder. This permits a closed model of the processes in the reaction media and at the surface of the sample during boriding to be discussed.     

Growth from the vapour by surface nucleation

The experimental conditions under which cadmium sulphide is grown from the vapour to form crystals having a (11.0) singular growth faces are calculated. This is done assuming that growth proceeds on these faces by one-dimensional surface nucleation. Calculations based on this assumption are compared with experimental observations on the habit of CdS, and the relationship between growth rate and supersaturation, and shown to be consistent with these.     

Preparation of single-crystalline ZnO films on ZnO-buffered a-plane sapphire by chemical bath deposition

High-quality zinc oxide (ZnO) films were successfully grown on ZnO-buffered a-plane sapphire (Al₂O₃ (1 1 2¯ 0)) substrates by controlling temperature for lateral growth using chemical bath deposition (CBD) at a low temperature of 60 °C. X-ray diffraction analysis and transmission electron microscopy micrographs showed that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. Rocking curves (ω-scans) of the (0 0 0 2) reflections showed a narrow peak with full width at half maximum value of 0.50° for the ZnO film. A reciprocal space map indicated that the lattice parameters of the ZnO film (a=0.3250 nm and c=0.5207 nm) were very close to those of the wurtzite-type ZnO. The ZnO film on the ZnO-buffered Al₂O₃ (1 1 2¯ 0) substrate exhibited n-type conduction, with a carrier concentration of 1.9×10¹⁹ cm⁻³ and high carrier mobility of 22.6 cm² V⁻¹ s⁻¹.     

Growth and etching of silicon in chemical vapour deposition systems; The influence of thermal diffusion and temperature gradient

In the growth of epitaxial silicon using SiCl₄ as source material it is known, that the growth rate at first increases with increasing p_SiCl4, but at higher p_SiCl4 decreases and finally becomes negative. The exact shape of the growth curve and especi ally the point of zero growth, where the etch rate counterbalances the growth rate, differs considerably amongst various investigators. This phenomenon was subject to theoretical considerations. Three models were evaluated: (i) a simple equilibrium model in which gas transport limited kinetics are used with one single diffusion coefficient for all species; (ii) an extended model using individual diffusion coefficients; (iii) a model as in (ii) but including the effect of thermal diffusion. It is shown that models (i) and (ii) do not give a general solution of the problem. The best results are obtained with model (iii). The growth rate appears to be very sensitive to the temperature gradient ▽T. As ▽T depends on the kind of apparatus used in the deposition process, it provides a reasonable explanation for the observed differences.     

Preparation and properties of microcrystalline silicon films using photochemical vapor deposition

microcrystalline silicon films have been prepared through mercury photosensitized decomposition of monosilane at low gas pressures. The dark and light conductivities of the silicon films tend to increase at reactant pressures lower than 65 Pa and become 10^?2Ω^?1· cm^?1 at 26 Pa. From the Raman scattering and x-ray diffraction, silicon films were found to consist of a mixed phase structure including both microcrystalline and amorphous regions.