Function Of Growth Time Research Articles

Structural characterization of CVD diamond films using the ESR method

The early deposition stages of diamond films have been studied in detail as a function of growth time, using electron spin resonance methods. The defect center in the non-diamond phase carbon region ( g = 2.003, ΔH pp = 8–14 Oe was observed from a sample deposited for 10 min. The defect center in the diamond layer ( g = 2.003, ΔH pp = 3–5 Oe) was observed together with the defect center in non-diamond phase carbon after 20 min of growth time, and the intensity of the defect center in the diamond layer increased gradually with prolonged deposition time. Moreover, the relationship between defect structures and electrical resistance of the diamond film was discussed.

The Mechanical Properties of a Thermoplastic Elastomer Produced by the Bacterium Pseudomonas oleovorans

Abstract PHO, a poly(β-hydroxyalkanoate) copolymer containing mostly β-hydroxyoctanoate repeating units, was produced in a fed batch fermentation process by Pseudomonas oleovorans when grown on sodium octanoate as the sole carbon source. The polymer from different batches—evaluated with regards to composition, molecular weight distribution, thermal transition temperatures, and decomposition temperature—was found to be highly consistent batch-to-batch. Polymer composition as a function of growth time did not change significantly once the culture reached the stationary growth phase. PHO when crystallized at room temperature from the melt, forms a physically crosslinked network with the crystalline regions acting as the physical crosslinks. The molecular weight between physical crosslinks was determined to be approximately 4000. The stress-strain properties, hardness, and tensile set of PHO were found to be within the range of values defined by a variety of commercially available thermoplastic elastomers with differing chemical structures. The tensile set of PHO was high, 35% after 100% elongation. Experimental evidence supports three possible sources of the high tensile set: permanent strain-induced orientation or displacement of the physical crosslinks, irreversible strain-induced crystallization, and deformation-induced changes of the size and purity/perfection of crystalline regions.

Behavior of the first layer growth in GaAs molecular beam epitaxy

The first layer growth in GaAs molecular beam epitaxy has been studied by reflection high-energy electron diffraction (RHEED). The time between the growth start and the first RHEED intensity peak is found to be dependent on the starting surface condition and is different from the time needed for a single layer growth. Periodic flux interruption has been used to study the surface recovery behavior as a function of growth time. When the growth time is the same as the time for a single layer growth, sustained two-dimensional growth can be obtained.

Asymmetric interface roughness in semiconductors grown by molecular-beam epitaxy

Computer simulations of crystal growth by molecular-beam epitaxy (MBE) are used to study the nature of surface (interface) roughness as the crystal is being grown. The simulations were done on a Cray X-MP computer using a 100×100 atom substrate. The results presented use parameters for gallium arsenide but can be generalized to other systems. The nature of the surface is presented in terms of three quantities: (1) reflection high-energy electron diffraction (RHEED) intensity; (2) step density, and (3) island size distribution; all of which are calculated directly from the simulated crystal and expressed as a function of growth time. The RHEED intensity is evaluated, within the kinematical approximation, for the ‘‘off-Bragg’’ specular condition using the surface atoms only. The step density is the number of monolayer steps (up or down) that a tiny man would take as he walked along the surface in either the (110) or (11̄0) direction. This quantity is normalized and evaluated along both directions on the surface as a function of time. It is in the step density that asymmetry of the order of 30% can be seen. The cause of the aforementioned asymmetry is shown to be due to anion incorporation mechanisms. Detailed analysis of anion incorporation along different configurations is presented, as well as important effects arising from anion to cation flux ratio.

The initial stage of LPE growth of InGaAsP on GaAs in the region of immiscibility

The LPE growth process during the initial growth stage in the immiscible region of In x Ga 1− x As y P 1− y layers lattice-matched to GaAs was studied for several solid compositions as a function of growth time t g. It was found that the LPE process in the region of immiscibility is classified into three stages as follows: (1) an LPE layer with rather good crystal quality grows because of stabilization by the mismatch strain energy, (2) the crystal quality of the layer becomes gradually worse with increasing t g, and the interface spinodal decomposition is accelerated because the crystal defects weaken the substrate strain stabilizing effect, and then (3) it is impossible to grow the layer. The interfacial spinodal decomposition is more rapid at the solid composition near the center of the immiscible region, and it is slower on a (111)B GaAs than on a (100) GaAs substrate.

Redistribution phenomenon of residual impurities in undoped GaAs epitaxial layers grown by MOCVD as a function of growth time

It is experimentally demonstrated that under certain growth conditions, the deposition time of intentionally doped single-crystal GaAs mono-epitaxial layers grown by Metallic-Organo-Chemical Vapor Deposition (MOCVD) on (100) GaAs substrates strongly influences the residual impurities content. Five samples, each grown with a different deposition period but under the same growth conditions and sequence were investigated. The residual impurities in the upper part of the epilayer (0.4μm to 1μm below the layer surface) were determined using C-V measurements. The results show that in this range of depth: (1) the residual impurity concentration is lower in layers deposited during longer periods, and higher in layers deposited during shorter periods; (2) the distribution profile of these impurities can be approximated as linear; (3) the impurity gradient is larger for layers deposited during shorter periods than in layers deposited during longer periods. The above relations between residual impurities and growth time may be important in developing procedures for GaAs devices fabricated by the MOCVD method.

Thickness of GaP liquid phase epitaxial layers grown by step-cooling, equilibrium-cooling, and ramp-cooling methods

Using three different cooling processes, a series of liquid phase epitaxial growth experiments for GaP are performed to determine layer thickness, d, as a function of growth time, t, and amount of supercooling temperature, Δ. Comparison is made with layer thickness predictions that are derived from a diffusion-controlled model. Good agreement is obtained for growth times, t, less than the diffusion time, τ, of solute in the melt. The results indicate that, in addition to GaAs and InP, the diffusion-controlled model generally provides good predictions for liquid phase epitaxial grown GaP layers thickness as well.

Variation of the thickness and composition of lpe InGaAsP, InGaAs, and InP layers grown from a finite melt by the step-cooling technique

Constant composition InGaAsP and InGaAs epitaxial layers can be grown using the step-cooling technique. However, the requirement of a fixed growth temperature limits the maximum thickness that can be obtained. The thickness of InGaAsP (λg = 1.15 µm@#@), InGaAs (λg = 1.68 µm), and InP liquid phase epitaxial layers grown on (100) InP sub-strates by the step-cooling technique has been measured as a function of growth time. (λg is defined as the wave-length corresponding to the band gap of the epitaxial layer). For long growth times, the effect of the finite growth solution becomes important, and beyond a distinct growth time, constant composition growth can no longer be maintained. The maximum constant composition layer thick-ness obtainable is not severely restricted by the fixed growth temperature, and from the experimental results this maximum thickness can be estimated for any melt size.

Effects of a finite melt on the thickness and composition of liquid phase epitaxial InGaAsP and InGaAs layers grown by the diffusion-limited step-cooling technique

The thickness of InGaAsP (λg=1.15 μm) and InGaAs (λg=1.68 μm) liquid phase epitaxial layers grown on (100) InP substrates by the step-cooling technique has been measured as a function of growth time. (λg is defined as the wavelength corresponding to the energy gap of the epitaxial layer.) For growth times much less than the shortest diffusion time τi=l2/Di of the melt constituents, where l is the melt height and Di is the diffusivity of each component in the melt, the thickness is consistent with diffusion-limited theory, and the composition is constant. The time at which the growth rate deviates sharply from diffusion-limited theory and beyond which constant composition growth can no longer be maintained has been determined for the melt size used in our experiments and can be estimated for any melt size.

Electron microscope study of intrinsic and extrinsic stacking faults, and twins in SOS at the early stage of epitaxial growth

Fine structures of the Si films on (1 1 02) sapphire have been studied by a lattice resolution TEM. The Si was deposited by the pyrolysis of silane in H 2 at 1000°C at a growth rate of 0.1μm/min. The samples for TEM were prepared by peeling off the Si films from the substrates after HF treatment. A film having a mean thickness of 500 Å was composed of (100) and {110} domains. The volume fraction of the {110} domains was more than 50% and about constant as a function of growth time. The {110} domains contained much higher density of microtwins than the (100) domains. These microtwins had various thicknesses including one atomic layer (intrinsic stacking faults) and two atomic layers (extrinsic stacking faults). The density of the intrinsic stacking faults was higher than those of extrinsic stacking faults and other twins. The {110} and (100) islands were nucleated independently and the microtwins were also present in the islands smaller than 500 Å in diameter.

Thickness and surface morphology of GaAs LPE layers grown by supercooling, step-cooling, equilibrium-cooling, and two-phase solution techniques

This paper deals with four different methods of LPE growth — the supercooling, step-cooling, equilibrium-cooling, and two-phase-solution techniques. The thickness of GaAs layers grown by each technique has been measured as a function of growth time. Except for layers grown by the two-phase-solution method, the data are in good agreement with simple theoretical equations derived here by assuming that the growth rate is determined by the rate of solute (As) diffusion toward the interface. The smoothest layers were obtained by the supercooling and step-cooling techniques, the roughest by the two-phase-solution method. The supercooling technique should be of considerable practical value because it yields very smooth layers of reproducible thickness over the range from tenths to tens of micrometers.

Thiaminase I of Bacillus thiaminolyticus

Bacillus thiaminolyticus Matsukawa and Misawa grows well on a synthetic medium. Its growth is stimulated by thiamine. Pyrithiamine and oxythiamine are not inhibitory at the concentrations tested. A spectrophotometric assay for thiaminase I activity was developed and used to follow the production and distribution of this enzyme as a function of growth time. Thiaminase I is found predominantly (>90%) outside the cells throughout the entire growth cycle. Thus it appears to be an exoenzyme.