Pressure and temperature dependence of Zn incorporation in metalorganic chemical vapour deposition grown GaAs and AlGaAs using diethylzinc as precursor

Phase formation of hexagonal wurtzite ZnO through decomposition of Zn(OH)2 at various growth temperatures using CBD method

Effects of growth temperature and reactor pressure on AlN thin film grown by metal-organic chemical vapor deposition

Epitaxial thin GaN films (∼60 nm) have been grown on a-plane sapphire substrates at different growth temperatures (500–700 °C) using laser molecular beam epitaxy (LMBE). The effect of growth temperatures on the structural and optical properties of GaN layers grown on low temperature (LT) GaN buffer on prenitridated a-sapphire have been studied systematically. The in situ reflection high energy electron diffraction pattern revealed the three-dimensional epitaxial growth of GaN films on a-sapphire under the adopted growth conditions. The full width at half maximum (FWHM) value of x-ray rocking curves (XRCs) along GaN (0002) and (10-12) planes decreases with increasing growth temperature. The FWHM values of (0002) and (10-12) XRC for the 700 °C grown GaN film are 1.09° and 1.08°, respectively. Atomic force microscopy characterization showed that the grain size of GaN increases from 30–60 to 70–125 nm with the increase in growth temperature as GaN coalescence time is shorter at high temperature. The refractive index value for the dense GaN film grown at 600 °C is obtained to be ∼2.19 at the wavelength of 632 nm as deduced by spectroscopic ellipsometry. Photoluminescence spectroscopy confirmed that the epitaxial GaN layers grown on a-sapphire at 600–700 °C possess near band edge emission at ∼3.39 eV, close to bulk GaN. The GaN growth at 700 °C without a buffer still produced films with better crystalline and optical properties, but their surface morphology and coverage were inferior to those of the films grown with LT buffer. The results show that the growth temperature strongly influences the structural and optical quality of LMBE grown epitaxial GaN thin films on a-plane sapphire, and a growth temperature of >600 °C is necessary to achieve good quality GaN films.

Zinc incorporation into InP grown by atmospheric pressure metalorganic vapor phase epitaxy has been studied systematically as a function of Zn source flow rate, substrate orientation, and growth temperature. Within the growth conditions for device quality layers, a Zn saturation level exists which varies with substrate orientation. The incorporation kinetics is analyzed using a surface adsorption-trapping model. We demonstrate that the Langmuir state of adsorption–desorption process is not established during growth due to the interruption of the surface processes by layer growth. The existence of a saturation level at a given growth condition indicates that Zn atoms incorporate at defect sites instead of the normal growth sites for In. Two parameters are used to characterize the properties of the surface defect, i.e., the capture cross section and the time of desorption for Zn atoms. The implication of these parameters and their substrate orientation and growth temperature dependencies are discussed.

This investigation deals with the effect of growth temperature on the microstructure, nitrogen content, and crystallinity of C–N nanotubes. The X-ray photoelectron spectroscopic (XPS) study reveals that the atomic percentage of nitrogen content in nanotubes decreases with an increase in growth temperature. Transmission electron microscopic investigations indicate that the bamboo compartment distance increases with an increase in growth temperature. The diameter of the nanotubes also increases with increasing growth temperature. Raman modes sharpen while the normalized intensity of the defect mode decreases almost linearly with increasing growth temperature. These changes are attributed to the reduction of defect concentration due to an increase in crystal planar domain sizes in graphite sheets with increasing temperature. Both XPS and Raman spectral observations indicate that the C–N nanotubes grown at lower temperatures possess higher degree of disorder and higher N incorporation.

ABSTRACTGallium nitride (GaN) films were grown on (0001) sapphire substrates at 1050°C by controlled evaporation of gallium (Ga) metal and reaction with ammonia (NH3) at a total reactor pressure of 800 Torr. Pure nitrogen (N2) was flowed directly above the molten Ga source to prevented direct reaction between the molten Ga and ammonia, which causes Ga spattering and GaN crust formation. At the same time, this substantially enhanced the Ga transport to the substrate. A simple mass-transport model based on total reactor pressure, gas flow rates and source temperature was developed and verified. The theoretical calculations and growth rate measurements at different ammonia flow rates and reactor pressures showed that the maximum growth rate was controlled by transport of both Ga species and reactive ammonia to the substrate surface.

Temperature dependency of the LPCVD growth of ZrC with the ZrCl 4–CH 4–H 2 system

Effect of growth temperature on InGaN/GaN heterostructures grown by MOCVD

There are many reports of ZnSe nanowire synthesis, but photoluminescence measurements on these nanowires indicate weak band-edge and high sub-bandgap defect emission. The two main contributors to the non-optimal photoluminescence are nanowire growth at high temperatures and unpassivated surface states. In this paper, the synthesis of II–VI core–shell nanowires by metal organic vapor phase epitaxy is reported. We demonstrate that larger bandgap shells that passivate the nanowire surface states can be deposited around the nanowires by increasing the partial pressures of the shell reactants without a large increase in growth temperature, allowing high quality material to be obtained. The deposition of nearly lattice-matched ZnMgSSe shells on the ZnSe nanowires increases the band-edge luminescent intensity of the ZnSe nanowires by more than four orders of magnitude and improves the band-edge to defect photoluminescence intensity ratio to 12 000:1. The corresponding full widths at half maximum of the band-edge exciton peaks of the core–shell nanowires can be as narrow as 2.8 nm. It is also shown that magnesium and chlorine can be incorporated into the ZnSe nanowire cores, which shortens the emission wavelength and is known to act as an n-type dopant, respectively.

Vertical growth characterization of InAs nanowires grown by selective area growth on patterned InP(1 1 1)B substrate by a MOCVD method

The level of the TEF3 mRNA, which encodes the fungal-specific translation elongation factor 3 (EF-3), was measured during the yeast-to-hyphal transition in Candida albicans. In contrast to a previous report, TEF3 mRNA levels were shown to change during dilution into fresh medium, increasing only transiently when dimorphism was induced by either (i) an increase in growth temperature (from 25 degrees C to 37 degrees C) combined with the addition of 10% (v/v) bovine calf serum to the medium, or (ii) an increase in growth temperature (from 25 degrees C to 37 degrees C) combined with an increase in the pH of the medium (from pH 4.5 to 6.5). TEF3 mRNA levels also increased in control cultures under conditions where germ tubes were not formed, but they remained elevated in contrast to cultures undergoing morphological changes. TEF3 mRNA levels were not significantly affected by heat-shock, but were tightly regulated during batch growth of the yeast form, reaching maximal levels in exponential phase. Therefore, the changes in TEF3 expression that accompany the dimorphic transition in C. albicans appear to reflect the underlying physiological changes that occur during morphogenesis and are not a response to morphogenesis per se. For this reason TEF3 mRNA measurement cannot be used as a loading control in Northern analyses of dimorphic gene regulation. Comparison of TEF3 mRNA levels with the abundance of the EF-3 polypeptide indicated that the synthesis of this essential translation factor might be subject to post-transcriptional regulation.

Recent advancements in β-Ga2O3 materials’ growth and device developments are briefly reviewed with the focus on low-pressure chemical vapor deposition (LPCVD) of β-Ga2O3. β-Ga2O3 films are grown on off-axis c-sapphire and (010) β-Ga2O3 substrates via high-temperature LPCVD (HT-LPCVD) with growth temperatures ranging between 950 and 1050 °C. The effects of HT-LPCVD growth conditions on material properties are comprehensively studied. With relatively higher growth temperatures, an increased O2 flow rate is required to maintain β-Ga2O3 crystalline quality with high electron mobility. The growth rate of the HT-LPCVD β-Ga2O3 film scales with the increase of growth temperature and O2 flow rate. The film growth rate is strongly related to the sapphire substrate off-axis angle, which determines the preferred nucleation sites from the step edges. The transport properties of samples grown on substrates with different off-axis angles are compared. The optimized growth temperature for obtaining films with high electron mobility varies with the off-axis angle. From this comprehensive study, high-quality β-Ga2O3 films grown on c-sapphire are achieved with room temperature mobilities of 126 cm2/V s (6° off-axis c-sapphire), 116 cm2/V s (8° off-axis c-sapphire), and 119 cm2/V s (10° off-axis c-sapphire) at carrier concentrations of mid-1016 cm−3. β-Ga2O3 LPCVD homoepitaxy optimized at elevated growth temperatures is performed on Fe-doped semi-insulating (010) Ga2O3 substrates. With controllable Si doping, record-high room temperature mobilities of 156 cm2/V s (150 cm2/V s) are achieved with doping concentrations of 3 × 1016 cm−3 (1.5 × 1017 cm−3) at a growth temperature of 1050 °C. Secondary ion mass spectroscopy analysis shows more than an order of magnitude reduction of C and H impurity incorporation with increased growth temperature. Results from this work demonstrate that HT-LPCVD growth is a promising method to produce high-quality β-Ga2O3 films on both off-axis c-sapphire and native Ga2O3 substrates with a fast growth rate and superior transport properties critical for high power device applications.

The relationship among growth temperature, membrane fatty acid composition, and pressure resistance was examined in Escherichia coli NCTC 8164. The pressure resistance of exponential-phase cells was maximal in cells grown at 10 degrees C and decreased with increasing growth temperatures up to 45 degrees C. By contrast, the pressure resistance of stationary-phase cells was lowest in cells grown at 10 degrees C and increased with increasing growth temperature, reaching a maximum at 30 to 37 degrees C before decreasing at 45 degrees C. The proportion of unsaturated fatty acids in the membrane lipids decreased with increasing growth temperature in both exponential- and stationary-phase cells and correlated closely with the melting point of the phospholipids extracted from whole cells examined by differential scanning calorimetry. Therefore, in exponential-phase cells, pressure resistance increased with greater membrane fluidity, whereas in stationary-phase cells, there was apparently no simple relationship between membrane fluidity and pressure resistance. When exponential-phase or stationary-phase cells were pressure treated at different temperatures, resistance in both cell types increased with increasing temperatures of pressurization (between 10 and 30 degrees C). Based on the above observations, we propose that membrane fluidity affects the pressure resistance of exponential- and stationary-phase cells in a similar way, but it is the dominant factor in exponential-phase cells whereas in stationary-phase cells, its effects are superimposed on a separate but larger effect of the physiological stationary-phase response that is itself temperature dependent.

Growth and characterization of unintentionally doped GaN grown on silicon(1 1 1) substrates

Growth and characteristics of PbS/polyvinyl alcohol nanocomposites for flexible high dielectric thin film applications