Influence Of Growth Parameters Research Articles

Aluminium Doping of 4H-SiC Grown with HexaMethylDiSilane

We report on the study of the p-type doping of 4H-SiC material using HexaMethylDiSilane/TriMethylAluminium/Propane (HMDS/TMA/P) system in place of the usual Silane/TriMethylAluminium/Propane (S/TMA/P) precursors. The influence of growth parameters such as TMA flow, growth rate or C/Si ratio is investigated. The aluminium incorporation level is deduced from both by C(V) (mercury probe) and SIMS measurements. The presence of aluminium in the layers is confirmed by non-destructive optical micro-Raman experiments. Good quality p-type, aluminium doped 4H-SiC layers can be grown using HMDS/TMA/P system. The amount of aluminium in the layers can be controlled by choosing the growth conditions and an aluminium concentration as high as 2x1019 at.cm-3 has been reached.Finally, comparing the two HMDS/TMA/P and S/TMA/P systems, no difference in aluminium incorporation has been found.

Intermixing in self-assembled InAs quantum dot formation

The influence of growth parameters and substrate material on the basic processes during strain-induced InAs-quantum dot (QD) formation and the resulting structural properties of the QDs is studied with reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), and X-ray diffraction. The process of strain-induced QD formation is strongly influenced by the intermixing with substrate material and the desorption of indium at high temperatures. From the experimental results, we conclude that the strain-energy modification due to temperature-dependent intermixing has a larger influence on QD formation than temperature-dependent kinetic processes at the surface. Interestingly, we also find that the maximum growth temperature limited by desorption depends on the growth speed.

Growth conditions required for bacteriocin production by strains of Staphylococcus aureus

The influence of growth parameters on the production of bacteriocins (aureocins) by five strains of Staphylococcus aureus was investigated. These aureocins have a broad spectrum of activity and can inhibit important human and animal pathogens. All strains produced large inhibition zones upon the indicator strain when they were grown in rich media such as brain-heart infusion (BHI), N2GT and 2 × YT. Bacteriocin production was not influenced by the initial pH of the medium (6.0–8.0). At lower temperature (28 °C), there was a marked reduction in bacteriocin production. Incubation of the producers under anaerobiosis affected profoundly the production of two related bacteriocins, aureocins MB92 and 146L, and slightly increased the production of aureocins A53 and 215FN. Production of aureocins MB92 and 215FN was apparently abolished in media containing ≥ 2.5 g and ≥ 3.5 g Nacl/100 ml, respectively. Although production of the remaining aureocins was observed in all NaCl concentrations tested (0.5–7.5 g/100 ml), the larger inhibition zones were detected in media containing up to either 1.5 g (for aureocins A70 and 146L) or 2.5 g NaCl/100 ml (for aureocin A53). Aureocin 215FN could not be detected in the culture supernatant. For the remaining aureocins tested, the highest levels of bacteriocin production occurred in either the late-log or early stationary growth phase of cultures grown in BHI medium at 37 °C. Changes in environmental conditions can, therefore, have detrimental effects on the production of active aureocins. Such factors are relevant when considering the potential biotechnological applications of these substances and when testing new S. aureus isolates for bacteriocin production.

Influence of growth parameters on the surface morphology and crystallinity of InSb epilayers grown by liquid phase epitaxy

Unintentionally doped homoepitaxial InSb films have been grown by liquid phase epitaxy employing ramp cooling and step cooling growth modes. The effect of growth temperature, degree of supercooling and growth duration on the surface morphology and crystallinity were investigated. The major surface features of the grown film like terracing, inclusions, meniscus lines, etc are presented step-by-step and a variety of methods devised to overcome such undesirable features are described in sufficient detail. The optimization of growth parameters have led to the growth of smooth and continuous films. From the detailed morphological, X-ray diffraction, scanning electron microscopic and Raman studies, a correlation between the surface morphology and crystallinity has been established.

Influence of substrate temperature on the chemical and microstructural properties of MO-CVD ZrTiO 4 thin films

In the last few years, intensive research activity has been focused on the development of suitable synthesis methods for high-permittivity materials, used for the realization of next-generation microdevices able to fulfil the previsions of the Technology Roadmap of Semiconductors. The use of high-permittivity materials can overcome the difficulties concerning the production of SiO2-based ultra-thin dielectrics, such as the generation of pinholes and the non-uniformity of the film, which may result in a malfunction in high-density systems. Recently, zirconium titanate thin films were discovered to have very interesting dielectric properties, which suggests a use for them in microwave integrated systems, such as receivers or DRAMs, since they are monophasic, have little dissipation and show a good thermal stability and a high value for the dielectric constant, independent of frequency in the range from kilohertz to a few gigahertz. Real application is possible only in strict connection with the development of a suitable preparation method which allows production with controlled and reproducible characteristics. In this work, the synthesis and characterization of ZrxTi1-xO4 (ZT) thin films grown via MO-CVD is described, studying the influence of growth parameters on their structural, chemical and physical properties.

Improved performance of MBE grown quantum-dot lasers with asymmetric dots in a well design emitting near 1.3 μm

To improve the performance of InAs/GaInAs quantum-dot lasers emitting near 1.3 μm, the influence of growth parameters and of the dot layer design were investigated. As starting point a symmetrically designed “dots in a well” (DWELL) structure was used. The thickness of the Ga 0.85In 0.15As layer grown before the InAs dot layer formation turned out to be one of the key parameters to control the dot morphology. The best optical properties were achieved by an asymmetric quantum well design with a 1 nm thick GaInAs layer below and 5 nm above the InAs dot layer. With this design the linewidth of the dot ground state transition could be reduced to 30 meV and the level separation could be increased to 75 meV. In comparison to lasers with symmetric DWELLs, the threshold current could be reduced by 50%, and an increased T 0 value of 130 K up to 40°C could be obtained.

Influence of growth parameters on the structure of YBCO thin films prepared by sequential deposition and annealing

Influence of growth parameters on the structure of YBCO thin films prepared by sequential deposition and annealing

Influence of growth conditions on the production of a nisin-like bacteriocin by Lactococcus lactis subsp. lactis A164 isolated from kimchi

The influence of growth parameters on the fermentative production of a nisin-like bacteriocin by Lactococcus lactis subsp. lactis A164 isolated from kimchi was studied. The bacteriocin production was greatly affected by carbon and nitrogen sources. Strain A164 produced at least 4-fold greater bacteriocin in M17 broth supplemented with lactose than other carbon sources. The amount of 3% yeast extract was found to be the optimal organic nitrogen source. While the maximum biomass was obtained at 37 °C, the optimal temperature for the bacteriocin production was 30 °C. The bacteriocin production was also affected by pH of the culture broth. The optimal pH for growth and bacteriocin production was 6.0. Although the cell growth at pH 6.0 was nearly the same level at pH 5.5 and 6.5, the greater bacteriocin activity was observed at pH 6.0. Exponential growth took place only during an initial period of the cultivation, and then linear growth was observed. Linear growth rates increased from 0.160 g DCW l −1 h −1 to 0.245 g DCW l −1 h −1 with increases in lactose concentrations from 0.5 to 3.0%. Maximum biomass was also increased from 1.88 g DCW l −1 to 4.29 g DCW l −1. However, increase in lactose concentration did not prolong the active growth phase. After 20 h cultivation, cell growth stopped regardless of lactose concentration. Production of the bacteriocin showed primary metabolic kinetics. However, bacteriocin yield based on cell mass increased greatly during the late growth phase. A maximum activity of 131×10 3 AU ml −1 was obtained at early stationary growth phase (20 h) during the batch fermentation in M17L broth (3.0% lactose) at 30 °C and pH 6.0.

Molecular beam epitaxy synthesis of Si 1− yC y and Si 1− x− yGe xC y alloys and Ge islands using an electron cyclotron resonance argon/methane plasma

We report the growth of Si 1− y C y and Si 1− x− y Ge x C y alloys on Si(001) by electron cyclotron resonance plasma-assisted Si molecular beam epitaxy using an argon/methane gas mixture. Various Si/Si 1− y C y and Si/Si 1− x− y Ge x C y multilayers have been grown and characterized principally by X-ray diffraction and Raman spectroscopy. The influence of growth parameters and electron cyclotron resonance plasma source operating conditions on the C substitutional incorporation was studied. Under optimum growth conditions the structures show good structural properties and sharp interfaces with carbon being essentially substitutionally incorporated up to concentrations of ∼1%. No significant carbon incorporation was measured in films grown under a high methane partial pressure without plasma excitation. Si 1− x− y Ge x C y layers grown with this technique exhibit the strain compensation and enhanced thermal stability expected for these ternary alloys. Carbon pre-deposition of Si through surface exposure to the argon/methane plasma is shown to act as an antisurfactant on the growth of Ge islands by suppressing the formation of a Ge wetting layer on the surface.

Influence of growth parameters and melt convection on the solid–liquid interface during RF-floating zone crystal growth of intermetallic compounds

The influence of growth parameters and melt convection on the solid–liquid interface of the intermetallic compound Ni3Si grown by the RF-floating zone technique was investigated experimentally as well as numerically. Numerical simulations showed that the heat transfer is strongly influenced by the electromagnetically driven and Marangoni convections whereas both the buoyancy and feed rotation have a negligible effect. It was found experimentally that the inductor design, the rod diameter and the length of the molten zone influence the solid–liquid interface shape significantly. The electromagnetically driven convection increases dramatically with increasing zone length due to the rapid increase of the non-uniformity of the magnetic field. The minimisation of the zone length and the application of an after heater reduce concave (towards the melt) interface regions which give rise to polycrystalline segments during RF-floating zone crystal growth of complicated intermetallic compounds. However, the adjustment of a complete convex solid–liquid interface shape in RF-floating zone crystal growth requires some additional melt stirring, e.g. by magnetic forces.

Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapour deposition

ABSTRACTWe have investigated the nitrogen incorporation dependency on temperature, pressure, C/Si ratio and growth rate in a horizontal hot-wall CVD reactor. The incorporation mechanism for 4H- and 6H-SiC both for Si- and C-face material is presented. A comparison with previously published results in a cold-wall reactor is also made.

Theoretical study of the formation of deformation twins in GaAs crystals grown by the vertical gradient freeze method

The objective of this paper is to predict the twin formation in the Gallium Arsenide (GaAs) crystals grown by vertical gradient freeze (VGF) method at different growth parameters. The deformation twins are formed in the GaAs crystal during its growth processes from the melt. The thermal stresses generated by the temperature profile during the crystal growth can be the primary cause of deformation twin formation. Temperature gradients are depend on the geometrical and physical crystal growth parameters, such as crystal diameter and imposed temperature gradients on the surface of the solidifying crystal in VGF. A quantitative thermal stress model is developed here for predicting the twin formation in GaAs grown by VGF at different growth parameters. This investigation is expected to further the understanding of twin formation. This understanding will provide valuable information to crystal growers to study the influence of growth parameters on twin formation for growing low defect GaAs crystal.

Model of textural development of layered crystal aggregates

A two-dimensional computer model is developed to study the evolution of texture during the growth of layered mineral aggregates. The program computes the number, size and orientation (texture) of crystals forming the outer surface of the aggregate, as well as the evolution as a function of time. In particular, the analysis focuses on the influence of growth parameters such as the anisotropy of the growing crystal forms, the relative growth rate of the crystal faces, the nucleation density on the substrate surface, the flow direction of the mineralizing solution and the shape of the substrate. The simulation provides an explanation for the development of a preferential orientation in a polycrystalline material growing from randomly oriented nuclei. The calculated distribution of crystal orientations, and its evolution with time, is in agreement with textures observed in synthetic and natural polycrystalline aggregates.

Growth of thick 4H-SiC epilayers in a vertical radiant-heating reactor

ABSTRACTGrowth of very thick 4H-SiC epilayers up to 215 μm has been demonstrated in a vertical radiant-heating reactor. Surface roughness is maintained as small as ˜0.2 nm even for epilayers over 150 μm in thickness, and a regular step structure without macro step bunching is observed from the very thick epilayers indicating a stable step-flow growth. Photoluminescence and secondary ion mass spectroscopy (SIMS) were performed for a 150 μm-thick epilayer. The Photoluminescence showed strong free excitons and comparatively small nitrogen bound excitons, while aluminum-, boron- and titanium-related lines were almost negligible. The SIMS analysis found no impurities exceeding 1 × 1014 cm−3. The influence of growth parameters on thickness uniformity will also be shown.

Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapour deposition

AbstractWe have investigated the nitrogen incorporation dependency on temperature, pressure, C/Si ratio and growth rate in a horizontal hot-wall CVD reactor. The incorporation mechanism for 4H- and 6H-SiC both for Si- and C-face material is presented. A comparison with previously published results in a cold-wall reactor is also made.

Influence of the GaN Seed Layer and Growth Parameters on Selective Epitaxy of GaN by HVPE

Selective epitaxy of gallium nitride on patterned substrates has been carried out by Hydride Vapor Phase Epitaxy (HVPE). The influence of growth parameters, in particular of the V/III in the gas ambient and the mask geometry is reported. Two types of GaN seed layers, epitaxial or amorphous, have been used. Epitaxial overgrowth was carried out on 〈1 — 100〉 and 〈11 — 20〉 oriented stripe patterned substrates and coalescence was achieved leading to uniform GaN films. Photoluminescence recorded at 10 K exhibits a FWHM of 9 meV for the excitonic peak. X-ray diffraction mapping was performed and the FWHM of the ω scan is in the range of 280 to 480 arcsec.

Volatiles Produced by Staphylococcus xylosus and Staphylococcus carnosus during Growth in Sausage Minces Part II. The Influence of Growth Parameters

Aseptic model minces inoculated with commercial samples of either Staphylococcus xylosus orStaphylococcus carnosus were prepared in accordance with an experimental design investigating the effect of seven parameters: fermentation temperature, pH, salt, nitrate, glucose, ascorbate, and the access of air. Volatiles produced by the cultures were collected during growth, identified and quantified. The data were analysed by partial least squares regression. The results showed that oxygen in general had more influence on the aroma producing capacity of Staphylococcus xylosus than ofStaphylococcus carnosus which was more affected by nitrate and glucose. The two strains differed mostly with regards to pH. Aroma production by both strains was strongly related to growth—either positively or negatively depending on compound. Potent aroma compounds such as methyl-branched aldehydes and acids arising from degradation of leucine, isoleucine and valine, and aromatic compounds arising from phenylalanine were produced in lower amounts when the bacteria grew well, that is, produced cell mass, whereas the opposite was the case for compounds such as sulphides and ketones.

Si incorporation and Burstein–Moss shift in n-type GaAs

Silane (SiH 4) was used as an n-type dopant in GaAs grown by low pressure metalorganic vapor phase epitaxy using trimethylgallium (TMGa) and arsine (AsH 3) as source materials. The electron carrier concentrations and silicon (Si) incorporation efficiency are studied by using Hall effect, electrochemical capacitance voltage profiler and low temperature photoluminescence (LTPL) spectroscopy. The influence of growth parameters, such as SiH 4 mole fraction, growth temperature, TMGa and AsH 3 mole fractions on the Si incorporation efficiency have been studied. The electron concentration increases with increasing SiH 4 mole fraction, growth temperature, and decreases with increasing TMGa and AsH 3 mole fractions. The decrease in electron concentration with increasing TMGa can be explained by vacancy control model. The PL experiments were carried out as a function of electron concentration (10 17−1.5×10 18 cm −3). The PL main peak shifts to higher energy and the full width at half maximum (FWHM) increases with increasing electron concentrations. We have obtained an empirical relation for FWHM of PL, Δ E( n) (eV)=1.4×10 −8 n 1/3. We also obtained an empirical relation for the band gap shrinkage, Δ E g in Si-doped GaAs as a function of electron concentration. The value of Δ E g (eV)=−2.75×10 −8 n 1/3, indicates a significant band gap shrinkage at high doping levels. These relations are considered to provide a useful tool to determine the electron concentration in Si-doped GaAs by low temperature PL measurement. The electron concentration decreases with increasing TMGa and AsH 3 mole fractions and the main peak shifts to the lower energy side. The peak shifts towards the lower energy side with increasing TMGa variation can also be explained by vacancy control model.

Low temperature photoluminescence properties of Zn-doped GaAs

Dimethylzinc (DMZn) was used as a p-type dopant in GaAs grown by low pressure metalorganic chemical vapor deposition (MOCVD). The influence of growth parameters, such as, DMZn mole fractions, growth temperature, trimethylgallium (TMGa) mole fractions, substrate surfaces on the Zn incorporation have been studied. The surface morphology of the layers was measured by scanning electron microscopy (SEM). The hole concentrations and zinc (Zn) incorporation efficiency are studied by using Hall effect, electrochemical capacitance voltage (ECV) profiler, and low temperature photoluminescence (LTPL) spectroscopy as functions of hole concentration (10 17−1.5×10 20 cm −3) and experimental temperatures (4.2–300 K). The hole concentration increases with increasing DMZn and TMGa mole fractions and decreases linearly with increasing growth temperature. The main PL peak shifted to lower energy and the full width at half maximum (FWHM) increased with increasing hole concentration. An empirical relation for FWHM, Δ Ep, band gap, Eg, and band gap shrinkage, Δ Eg in Zn doped GaAs as a function of hole concentration were obtained. These relations are considered a useful tool to determine the hole concentration in Zn doped GaAs by low temperature PL measurement. The hole concentration increases with increasing TMGa mole fraction and the main peak is shifted to lower energy side.

Crystal growth of selected II–VI semiconducting alloys by directional solidification: Part I Ground-based experiments

A series of Hg0.84Zn0.16 Te crystal ingots have been grown from pseudobinary melts by the Bridgmam–Stockbarger type directional solidification using a Marshall Space Flight Center/Space Science Laboratory heat-pipe furnace and the ground control experiment laboratory furnace of the crystal growth furnace which was flown on the first United States Microgravity Mission. A number of translation rates and a series of hot- and cold-zone temperatures were employed to assess the influence of growth parameters on the crystal properties for the purpose of optimizing the in-flight growth conditions.