Aluminum nitride (AlN) epitaxial layer on sapphire substrate was grown at high temperatures above View the MathML source by hydride vapor phase epitaxy (HVPE). A high-temperature growth system was built by combining a conventional hot-wall type furnace and a heating susceptor with integrated heating element. This system realized growth of AlN by HVPE above View the MathML source even in the quartz reactor. Growth rates of AlN stay constant in the temperature range of View the MathML source. This result was consistent with the results expected from thermodynamic analysis, and represents that growth of AlN by HVPE is under mass transportation limited process even at high temperatures. Epitaxial growth of AlN with growth rate of View the MathML source was achieved at View the MathML source.

The annealing behavior under cw Ar laser irradiation (Li) has been studied for 0.2–0.5‐μm‐thick silicon‐on‐sapphire (SOS) epitaxial films. Analysis by MeV He+ channeling shows that after LI in the solid phase, Si‐implanted films, which had a buried amorphous layer beneth ≈30 Å of surface crystal, become crystalline, but are more defective than the original chemically vapor‐deposited (CVD) films. By contrast, furnace annealing of similar layers significantly reduces the defect concentrations below the surface crystal, compared to the defect level in CVD SOS. LI of CVD or Si‐implanted SOS in the liquid phase reduces the defect concentration throughout the film thickness, but the regrown films are laterally nonuniform and have a high Al content.


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Chemical vapor deposition (CVD) using gold nanoparticles as the catalyst to grow high-quality single-crystal gallium nitride nanowires was developed. This method enables control over several important aspects of the growth, including control of the nanowire diameter by using monodispersed gold clusters, control of the nanowire location via e-beam patterning of the catalyst sites, and control of the nanowire orientation via epitaxial growth ona-plane sapphire substrates. Our work opens up new ways to use GaN nanowires as nanobuilding blocks.

The diffusion of oxygen in sapphire was accelerated by heating in a 28 GHz microwave furnace as compared with heating in a conventional furnace. Tracer diffusion experiments were conducted using 18O. Single crystal sapphire wafers with a (1 0 1 2) rhombohedral planar orientation were used as the substrate. Concentration depth profiling was done by proton activation analysis using a 5 MeV Van de Graaff accelerator. The diffusion of 18O was greatly enhanced by microwave heating as compared with conventional heating in the 1500–1800°C range. The apparent activation energy for 18O bulk diffusion was determined to be 390 kJ mol-1 with microwave heating and 650 kJ mol-1 with conventional heating.


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The world's largest sapphire boules up to 340-mm diameter are produced by the Heat Exchanger Method (HEM). In order to meet all applications, the highest purity crackle is used so the product has impurity levels very near the detectability limit of Glow Discharge Mass Spectroscopy (GDMS). The charge size of production 340-mm diameter sapphire boules was increased from 55-kg to 70-kg, and larger 380-mm diameter, 84-kg boules were produced. These boules were used to produce 315-mm diameter, 132-mm high sapphire cylinders to meet customer requirements. Efforts have been taken to produce a nearly flat top surface of HEM-grown boules with minimal undulations along the sidewalls to allow fabrication of larger sapphire pieces for production boules.Up-scaling of the gradient furnace technique has resulted in the growth of large monocrystals of Al2O3 up to 15 cm in diameter, 6.8 cm in height, and 4.5 kg in weight.

The technique was developed to detect the crystallization of the upper-central surface of sapphire crystals grown in crucibles. This technique takes advantage of the large difference in optical absorption coefficients of molten and solid sapphire at the melting point, and is based on the recording of pyrometer readings throughout the course of growth. At the point of solidification of the observed sapphire surface, a knee occurs on the recorded graph. The accumulated data enable the optimization of growth rates at the end of the growth as well as the duration of the growth by proper timing of the beginning of crystal cool-down. It is also possible to detect and terminate unsuccessful growth runs at an early stage.


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Sapphire crystals, 140 mm in diameter and 90 mm in height, have been grown by temperature gradient techniques (TGT). The growth direction of the boule was fixed by means of Laue X-ray diffraction. A prominent 204 nm absorption band in TGT-Al2O3, which does not appear in single crystals grown by Czochralski method has been studied. Analysis further substantiates the F-center model of this band. Two relatively weaker bands absorbing at 232 nm and 254 nm were ascribed to F+ centers. F-type centers concentration was determined using Smakula's equation.

CdTe crystals were obtained using a vapour phase method, where the crystal is grown on a monocrystalline seed without contact with a heat-conducting supporter. Some different agents filling the tube during the growth process were used and it was found that the growth rate depends strongly on the agent.


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The etching of sapphire substrates using H2SO4, H3PO4, and a 3:1 H2SO4:H3PO4 mixture, as a function of temperature and etching time, was systematically studied using atomic force microscopy. The sapphire preparation by liquid-based etchings was compared with H2 etching at 1100°C and air-annealing at 1400°C. In liquid-based treatments, the smoothest, pit-free surface was obtained by etching in pure H2SO4 at 300°C for 30 min. Sulfuric acid etching at higher temperatures or for longer periods generated an insoluble mixture of Al2(SO4)3 and Al2(SO4)3⋅17H2O crystalline deposits on the surface.

Phosphoric acid and the 3:1 H2SO4:H3PO4 mixture, which is the routinely employed chemical treatment for sapphire preparation, etched the sapphire preferentially at defect sites and resulted in pit formation on the surface. Sapphire treatment using H2 at 1100°C did not remove the surface damage. Air annealing the sapphire at 1400°C for 1 h produced an atomically smooth surface consisting of a terrace-and-step structure. The results of this study were described in terms of the chemistry of the sapphire etching process.


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Shaped sapphire crystals obtained by the edge-defined film fed growth (EFG) method almost always contain a typical defect, the so-called “voids”, which affect the optical quality of the crystals. The origin of the trapped voids is not yet clarified. One of the hypotheses is concerned with gas formation in the crystal growth setup chamber. The goal of this paper is to study the species of the gases resulting from various chemical reactions between the different components of the crystal growth apparatus, such as the charge (Al2O3), the crucible and the shaper material (Mo or W) and the screens and other details made from graphite (C).

In order to obtain the partial pressure of the gas species in the growth chamber the thermodynamic calculations were performed using the complex equilibrium code—Gemini2—that minimizes the free enthalpy formation. Carbon monoxide (CO) becomes the most important gas species when one of the growth setup components is made from graphite. The various gas species resulting from different reactions are trapped in the crystal during the growth process and affect the crystal quality.In order to eliminate the contamination of the crystals, this type of calculation should be profitable for a better choice of the crucible, shaper and other set-up detail material.


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The properties of sapphire make it an ideal choice for future high speed missile applications compared to other existing or emerging materials. High fabrication cost and low material utilization from a sapphire boule cause high costs for sapphire domes. Significant improvements have been made by growing sapphire boules with orientation and contour slicing. A more desirable approach is to produce near net-shaped sapphire blanks directly from the melt. The feasibility of producing crack-free near net-shaped blanks with controlled inside and outside curvature from the melt in orientation has been demonstrated using the Heat Exchanger Method (HEM).

Semiconducting β‐FeSi2 films grown on‐oriented Si and on(11¯02)‐sapphire substrates are investigated by x‐ray diffraction, Nomarski optical microscopy, stress, and surface roughness measurements. As a result of an exothermic, nucleation controlled reaction, we observe a characteristic ring‐shaped surface pattern of the silicide. Surface roughness and stress in β‐FeSi2 are less pronounced for films grown at lower temperatures and cooling rates. Sapphire substrates result in smoother surfaces than Si due to the match of the thermal expansion coefficient of sapphire to the silicides.


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The effect of the RF coil position during the stages of sapphire crystal growth process in an inductively heated Czochralski crystal growth furnace on the thermal and flow transport, the shape of the crystal–melt interface shape, and the power requirements is investigated numerically. The results show that although the maximum values of temperature and velocity decrease, the convexity of the crystal–melt interface increases as the crystal length grows. It is found that the least input power is required if the central position of the RF coil is maintained below the central position of the melt during the crystal growth process. Under such crystal growth conditions, the temperature gradients along the crystalline front are small.

Sapphire thin films, typically 10 μm thick, on undoped sapphire substrates using pulsed laser deposition from a Ti:sapphire single crystal target with a doping level of 0.1 wt.% Ti2O3. These thin films are shown to have very high crystal quality using ion beam channelling and X-ray diffraction techniques. The degree of titanium incorporation into the films is investigated using inductively coupled plasma mass spectrometry and particle induced X-ray emission. These techniques show that levels of up to 0.08 wt.% Ti2O3 are present in the deposited layers.


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Patterned growth of vertically aligned ZnO nanowire arrays on the micrometer and nanometer scale on sapphire and GaN epilayers is reported. In order to control the position and distribution density of the ZnO nanowires, Au seeding nanodots are defined, as regular arrays, with the assistance of deposition shadow masks. Electron micrographs reveal that the wires are single crystals having wire axes along the hexagonal c-axes. The epitaxial growth of ZnO nanowires on sapphire and GaN films on Si substrates was further verified by cross sectional electron microscopy investigations. Compared to the sapphire case, the perfect epitaxial growth on a GaN film on a Si substrate is believed to be more suitable for potential electronic device applications of ZnO nanowire arrays.

An r.f. furnace and control equipment that are suitable for growing single crystals of refractory oxides, such as Al2O3, by the Czochralski technique is described and examples of sapphire and ruby boules grown using this equipment are shown. Thoria is employed throughout the furnace. Thoria has a lower heat capacity and a higher resistivity at the working temperature than any other refractory oxide. This enables iridium susceptor crucibles to be used at temperatures close to their melting point.


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We provide an overview of the latest market trends and modern competing methods of sapphire crystal growth and the application of sapphire wafers as LED substrates. Almost all methods of high temperature growth from the melt are suitable for sapphire production, but each of these methods has its advantages and disadvantages depending on the application and required finished product form factor. Special attention is paid to the review of defects and imperfections that allow the engineering of new active devices based on sapphire.

An internally heated pressure vessel was used to study the decomposition reaction of GaN at temperatures above 900°C and the phase equilibria in the system Ga-N2. As a consequence of these studies we have undertaken the crystal growth of GaN free crystals and epitaxial layers on sapphire by a VLS process. We have succeeded in the synthesis of high quality epitaxial layers showing the terrace structure typical of LPE. As a function of the growth conditions both n and p type gallium nitride were obtained, the latter only in polycrystalline form.


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