Numerical Simulation of Heat Transfer and Kinetics in the Bulk Growth of Silicon Carbide

The growth process of 2-inch silicon carbide (SiC) single crystals by the physical vapor transport method (or modified Lely method) has been modeled and simulated. The comprehensive process model incorporates the calculations of radio frequency (RF) induction heating, heat and mass transfer and growth kinetics. The transport equations for electromagnetic field, heat transfer, and species transport are solved using a finite volume-based numerical scheme called MASTRAPP (Multizone Adaptive Scheme for Transport and Phase Change Process). Temperature distribution for a 2-inch growth system is calculated, and the effects of induction heating frequency and current on the temperature distribution and growth rate are investigated. The predicted results have been compared with the experimental data.

3D Finite Volume Scheme for Czochralski Crystal Growth

A general three-dimensional model is developed for simulation of the growth process of silicon single crystals by Czochralski technique. The numerical scheme is based on the curvilinear non-orthogonal finite volume discretization. Numerical solutions show that the flow and temperature fields in the melt are asymmetric and unsteady for 8’’ silicon growth. The effects of rotation of crystal on the flow structure are studied. The rotation of crystal forms the Ekman layer in which the temperature gradient along solid/melt surface is small.

3D Finite Volume Scheme for Czochralski Single Crystal Growth

Czochralski (Cz) technique, which is used for growing single crystals, has dominated the production of single crystals for electronic applications. The Cz growth process involves multiple phases, moving interface and three-dimensional behavior. Much has been done to study these phenomena by means of numerical methods as well as experimental observations. A three-dimensional curvilinear finite volume based algorithm has been developed to model the Cz process. A body-fitted transformation based approach is adopted in conjunction with a multizone adaptive grid generation (MAGG) technique to accurately handle the three-dimensional problems of phase-change in irregular geometries with free and moving surfaces. The multizone adaptive model is used to perform a three-dimensional simulation of the Cz growth of silicon single crystals.Since the phase change interface are irregular in shape and they move in response to the solution, accurate treatment of these interfaces is important from numerical accuracy point of view. The multizone adaptive grid generation (MAGG) is the appropriate scheme for this purpose. Another challenge encountered is the moving and periodic boundary conditions, which is essential to the numerical solution of the governing equations. Special treatments are implemented to impose the periodic boundary condition in a particular direction and to determine the internal boundary position and shape varying with the combination of ambient physicochemical transport process and interfacial dynamics. As indicated above that the applications and processes characterized by multi-phase, moving interfaces and irregular shape render the associated physical phenomena three-dimensional and unsteady. Therefore a generalized 3D model rather than a 2D simulation, in which the governing equations are solved in a general non-orthogonal coordinate system, is constructed to describe and capture the features of the growth process. All this has been implemented and validated by using it to model the low pressure Cz growth of silicon. Accuracy of this scheme is demonstrated by agreement of simulation data with available experimental data. Using the quasi-steady state approximation, it is shown that the flow and temperature fields in the melt under certain operating conditions become asymmetric and unsteady even in the absence of extrinsic sources of asymmetry. Asymmetry in the flow and temperature fields, caused by high shear initiated phenomena, affects the interface shape in the azimuthal direction thus results in the thermal stress distribution in the vicinity, which has serious implications from crystal quality point of view.

Numerical Simulation of the Flow Field and Concentration Distribution in the Bulk Growth of Silicon Carbide Crystals

The physical vapor transport (PVT) method is being widely used to grow large-size single SiC crystals. The growth process is associated with heat and mass transport in the growth chamber, chemical reactions among multiple species as well as phase change at the crystal/gas interface. The current paper aims at studying and verifying the transport mechanism and growth kinetics model by demonstrating the flow field and species concentration distribution in the growth system. We have developed a coupled model, which takes into account the mass transport and growth kinetics. Numerical simulation is carried out by employing an in-house developed software based on finite volume method. The results calculated are in good agreement with the experimental observation.

Crystal growth and optical properties of Gd1.99-xYxCe.0.01SiO5 single crystals

Gd1.99-xYxCe0.01SiO5 (Ce:GYSO) crystals (x = 0, 0.0995, 0.199) have been grown by the Czochralski (Cz) method. Crystal structure and the distribution coefficients of Ce have been determined for all three crystals. Spectroscopic measurements indicate that optical transmittance and luminescence intensity of Gd1.99-xYxCe0.01SiO5 (x = 0.0995, 0.199) crystals are Substantially higher than those of Ce:Gd2SiO5 (Ce:GSO), especially at x = 0.0995, which makes them good candidate materials for scintillation applications. The particularly important result is that the alloyed Ce:GYSO crystals can be grown easily by the Cz method and, unlike Ce:GSO, they do not undergo cleavage during the growth process or subsequent mechanical treatment. (c) 2005 Elsevier B.V. All rights reserved.

Edge-defined, film-fed growth (EFG) technique for the preparation of alpha-Al2O3 : C crystal with highly sensitive thermoluminescence response

In this work, alpha-Al2O3:C, a highly sensitive thermoluminescence dosimetry crystal, was grown by the EFG method in which a graphite heating unit and shield acted as the carbon source during the growth process. The optical, luminescent properties and dosimetric characteristics of the crystal were investigated. The as-grown crystal shows a single glow peak at 536 K, which is associated with Cr3+ ions. After annealing in H-2 at 1673 K for 80 h, the crystal shows a single glow peak at 460 K and a blue emission band at 415 nm. The thermoluminescent response of the annealed crystal shows linear-sublinear-saturation characteristics in the dose range from 5 x 10(-6) to 100 Gy.

Defect evolution and accompanied change of electrical properties during the GaN growth by metalorganic chemical vapor deposition

The defect evolution and its correlation with electrical properties of GaN films grown by metalorganic chemical vapor deposition are investigated. It is found that the dislocation density decreases gradually during the growth process, and the dislocation reduction rate in the island coalescence process is especially rapid. The changes in electron mobility of GaN with the increase of growth time are mainly dependent on the dislocations acting as scattering centers. Furthermore, the variation of carrier concentration in GaN may be related with the point defects and their clusters. The quality of GaN could be improved by suitably increasing the film thickness. (C) 2009 Elsevier B.V. All rights reserved.

Surface morphology of AlN buffer layer and its effect on GaN growth by metalorganic chemical vapor deposition

The in situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above low-temperature AlN buffer layer on c-plane sapphire substrate by metalorganic chemical vapor deposition. It is found that the lateral growth of GaN islands and their coalescence is promoted in the initial growth stage if the AlN buffer layer is treated with a long annealing time and has an optimal thickness: As confirmed by atomic force microscopy observations, the quality of GaN epilayers is closely dependent on the surface morphology of AlN buffer layer, especially the grain size and nuclei density after the annealing treatment. (C) 2004 American Institute of Physics.

Growth of ZnO single crystal by chemical vapor transport method

ZnO crystals were grown by CVT method in closed quartz tube under seeded condition. Carbon was used as a transport agent to enhance the chemical transport of ZnO in the growth process. ZnO single crystals were grown by using GaN/sapphire and GaN/Si wafer as seeds. The property and crystal quality of the ZnO single crystals was studied by photoluminescence spectroscopy and X-ray diffraction technique.

Parasitic reaction and its effect on the growth rate of AlN by metalorganic chemical vapor deposition

The Al composition of metalorganic chemical vapor deposition (MOCVD)-grown AlGaN alloy layers is found to be greatly influenced by the parasitic reaction between ammonia (NH3) and trimethylaluminum (TMAI). The growth process of AlN is carefully investigated by monitoring the in situ optical reflection. The abnormal dependencies of growth rate on growth temperature, reactor pressure, and flux of NH3 are observed and can be well explained by the effect of parasitic reaction. The increase of growth rate with increasing flux of TMAI is found to depend on the growth temperature and reactor pressure due to the presence of parasitic effect. A relatively low growth temperature and a reduced reactor pressure are suggested for the effective decrease of parasitic reaction during the MOCVD growth of AlN and probably lead to a more effective incorporation of Al into the AlGaN layers. (c) 2005 Elsevier B.V. All rights reserved.

Optimization of cubic GaN growth by metalorganic chemical vapor deposition based on residual strain relaxation

The reduction of residual strain in cubic GaN growth by inserting a thermoannealing process is investigated. It is found that the epilayer with smaller tensile strain is subject to a wider optimal "growth window." Based on this process, we obtain the high-quality GaN film of pure cubic phase with the thickness of 4 mum by metalorganic chemical vapor deposition. The photoluminescence spectrum at room temperature shows the thick GaN layer has a near-band emission peak with a full width at half maximum of 42 meV which confirms its high crystal quality, further supported by the x-ray (002) diffraction measurement. A simplified model is demonstrated to interpret this strain effect on the growth process. (C) 2003 American Institute of Physics.

The growth morphologies of GaN layer on Si(111) substrate

The growth morphologies of metalorganic chemical vapor deposition (MOCVD) grown GaN layer on Si(111) substrate were studied using atomic force microscopy and transmission electron microscopy. It was found that the growth process of GaN/Si(111) consisted of two cycles of island growth and coalescence. These two cycles process differs markedly from that of one cycle process reported. The stress of evolving GaN layers on Si(111) was characterized by measuring the lattice constant c of GaN using X-ray diffraction (XRD) technique. It was proposed that the large tensile stress within the film during growth initiated this second island growth cycle, and the interaction between the GaN islands with high orientational fluctuation on the buffer layer induced this large tensile growth stress when coalescence occurred. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of in situ thermal treatment during growth on crystal quality of GaN epilayer grown on sapphire substrate by MOVPE

GaN epilayers on sapphire substrate grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal-type low-pressure two-channel reactor were investigated. Samples were characterized by X-ray diffraction (XRD), Raman scattering, atomic force microscopy (AFM) and photoluminescence (PL) measurements. The influence of the temperature changes between low temperature (LT) deposited GaN buffer and high temperature (WT) grown GaN epilayer on crystal quality of epilayer was extensively studied. The effect of in situ thermal annealing during the growth on improving the GaN layer crystal quality was demonstrated and the possible mechanism involved in such a growth process was discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

The growth of SiC on Si substrates with C2H4 and Si2H6

SiC was grown on Si (100) substrates oriented and off-oriented by 2-5 degrees towards [011] with simultaneous supply of C2H4 and S2H6 at 1050 degrees C. SiC formed during removal of oxide could be removed at 1150 degrees C. Twinned growth occurred on both oriented and off-oriented substrates during carbonization, but fewer twins formed on the off-oriented substrate than that on the oriented substrate. In SiC growth process, twinned growth continued on the off-oriented substrate whereas twinned growth stopped and single crystal SiC with double-domain (2 x 1) superstructure formed on the oriented substrate. SiC single crystal could grow on a carbonized twinned buffer layer. Obvious SiC LO and TO phonon modes were observed with Raman spectroscopy in the epilayer grown on the oriented substrate. The surface of the epilayer grown on the oriented substrate was smooth, while there was a high density of islands on the epilayer grown on the off-oriented substrate. The film grown on the oriented substrate is superior than that grown on the off-oriented substrate. (C) 1999 Elsevier Science B.V. All rights reserved.

The dependence of growth rate of GaN buffer layer on growth parameters by metalorganic vapor-phase epitaxy

The growth rate of GaN buffer layers on sapphire grown by metalorganic vapor-phase epitaxy (MOVPE) in an atmospheric pressure, two-channel reactor was studied. The growth rate, as measured using laser reflectance, was found to be dependent on growth temperature, molar flow rate of the sources tin this case, trimethylgallium and ammonia) and the input configuration of sources into the reactor. A model of the GaN buffer layer growth process by MOVPE is proposed to interpret the experimental evidence. (C) 1998 Elsevier Science B.V. All rights reserved.