Yasuo Kitou

High-Quality SiC Bulk Single Crystal Growth Based on Simulation and Experiment

The numerical simulation and in-situ X-ray topography were applied to observe the phenomena inside a crucible. Numerical simulation pointed out that macroscopic grown crystal quality such as grown crystal shape strongly depends on the temperature distribution inside a crucible. In-situ X-ray topography revealed that when the defects were generated, and how the defects were propagated. Most of defects were generated at the initial growth stage. It is important to control the initial stage in order to obtain a high quality SiC single crystal. Numerical simulation also suggested that it is important reduce the residual stress in a grown crystal in order to avoid the dislocation occurrence. From these results based on numerical simulation and experiment, SiC sublimation growth was controlled actively, and the large and high quality SiC single crystal have been grown. Introduction Silicon carbide single crystal is usually grown by sublimation (modified Lely method). Since the first report of modified Lely method [1], more than 20 years has passed. However, there is a lot of remaining issues that should be solved. The main reason of this situation is that sublimation process is a black box process inside a closed carbon crucible above 2000 K. It is so difficult to know what going on inside a crucible, that it is much difficult to control the sublimation process actively. In order to overcome this point, the authors have applied the numerical simulation to see the phenomena inside a furnace [2,3,4,5]. The authors also developed the in-situ X-ray topography system to observe the crystal growth features inside a closed carbon crucible [6,7]. By using these observation tools, the SiC sublimation growth could be understand more detail [7,8,9,10], and could be controlled actively [3,11,12]. In this paper, the observation results and the example active control of SiC sublimation growth are described. Simulation The configuration of numerical modeling was based on the conventional RF induction-heating furnace that we used in experiments. Electromagnetic and thermal fields were analyzed by the commercial software, Flux-Expert [13,14], and CFD-ACE+[15]. Since convective heat transfer could be neglected in our experiments, the equation for momentum transfer was not analyzed. From the thermal fields, the concentration distribution of sublimated species was analyzed according to the LTCE model [13]. The residual stress in a grown crystal was also analyzed. Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 29-34 doi:10.4028/www.scientific.net/MSF.457-460.29

In-situ observation of silicon carbide sublimation growth by X-ray topography

The crystal growth of silicon carbide (SiC) was studied by in-situ observation using X-ray topographic technique. The growth was performed by a sublimation method (the modified Lely method). The generation and evolution of defects and dislocations were observed as topographs in a real-time display. Defects and dislocations analyzed by the in-situ technique were compared with the postprocess observations using optical microscopy and X-ray topography. Dislocations in the initial growth layer and typical large defects, such as micropipes, macrodefects and domain boundaries, were investigated. We showed the possibility that large defects are induced by the accumulation of dislocations in the initial growth layer. Moreover, we observed that inhomogeneous growth starting in parts on the seed surface during the initial growth results in new defects in the growing crystal. We discuss the importance of dislocation and nucleation control on the SiC seed crystal during the initial growth, on the basis of facts and findings obtained by the in-situ as well as postprocess observations.

SiC HTCVD Simulation Modified by Sublimation Etching

High temperature chemical vapor deposition (HTCVD) simulations of silicon carbide (SiC) were demonstrated with experimental results. A vertical cylindrical reactor was used in an RF inductive heating furnace and the temperature was more than 2200. SiH4 and C3H8 were used as source gases and H2 as carrier gas. A gas phase reaction model from the literature was used on the condition that the gas phase reaction is a quasi-equilibrium state. It was found that the major species were Si, Si2C, SiC2 and C2H2 in the gas phase reaction model as well as in the thermodynamic equilibrium calculation. Sublimation etching was considered in the surface reaction rates by modifying partial pressures of species with equilibrium vapor pressures. CFD-ACE+ and MALT2 software packages were used in the present calculation. The sticking coefficients were determined by fitting the calculated growth rates to the experimental ones. The simulated growth rate in a different reactor is in good agreement with the experimental value, using the same sticking coefficients. The present simulation could be useful to design a new reactor and to find optimum conditions.

The dissociation modes of threading screw dislocations in 4H-SiC

In 4H-SiC, which is currently considered as a most promising candidate for the power devices, four types of threading dislocation (TD) have been identified. Apart from a threading edge dislocation with b = a, it has been shown recently that there are at least three types of TDs whose Burgers vectors b are parallel or nearly parallel to the c axis, i.e. a threading pure screw dislocation (TpSD) with b = [0001], a threading near screw dislocation (TnSD) with and a threading mixed dislocation (TMD) with . These dislocations have been called simply as threading screw dislocations (TSDs). Since the total Burgers vector, and hence the energy, increases in the order of TpSD, TnSD and TMD, it is expected that the occurrence should decrease in the order of TpSD, TnSD and TMD. This is not the case. The reason why high-energy TnSD and TMD are as abundant as low-energy TpSD has been discussed based on the dissociation models. As a result of dissociation, the difference of energy among these three types of TSD is reduced considerably.

Direct Growth of AlN Single Crystal on Sapphire by Solution Growth Method

AlN was directly grown on a sapphire substrate by the solution growth method with the Cu–Si–Al–Ti solvent under a nitrogen gas flow. X-ray diffraction measurements revealed that the grown AlN was single crystal. The AlN layer was epitaxially formed on the sapphire substrate with the orientation relationships: (0001)AlN ∥(0001)sapphire and [100]AlN ∥[110]sapphire. The full widths at half maximum (FWHMs) of X-ray rocking curves for tilt and twist components were 414 and 2031 arcsec, respectively.

Computational Evaluation of Electrical Conductivity on SiC and the Influence of Crystal Defects

The main electronic characteristics of silicon carbide (SiC) are its wide energy gap, high thermal conductivity, and high break down electric field which make of it of one of the most appropriate materials for power electronic devices. Previously we reported on a new electrical conductivity evaluation method for nano-scale complex systems based on our original tight-binding quantum chemical molecular dynamics method. In this work, we report on the application of our methodology to various SiC polytypes. The electrical conductivity obtained for perfect crystal models of 3C-, 6H- and 4H-SiC, were equal to 10-20-10-25 S/cm. For the defect including model an extremely large electrical conductivity (of the order of 102 S/cm) was obtained. Consequently these results lead to the conclusion that the 3C-, 6H-, and 4H-SiC polytypes with perfect crystals have insulator properties while the electrical conductivity of the crystal with defect, increases significantly. This result infers that crystals containing defects easily undergo electric breakdown.

Simulation Study for HTCVD of SiC Using First-Principles Calculation and Thermo-Fluid Analysis

A simulation study for high temperature chemical vapor deposition (HTCVD) of silicon carbide (SiC) is presented. Thermodynamic properties of the species were derived from the first-principles calculations in order to evaluate the activation energy (Ea) in the gas phase reaction. Pathways producing SiC2 and Si2C from SiCl4-C3H8-H2 system were proposed to investigate the effect of chlorinated species on HTCVD. A thermo-fluid analysis was carried out to estimate the partial pressures of the species. It was found that the main sublimed species of Si, SiC2, Si2C decreased in the SiCl4-C3H8-H2 system compared to the SiH4-C3H8-H2 system. This suggests that the growth rate would decrease in the atmosphere of chlorinated species at around 2500°C.

Inclination of a threading dislocation in an epilayer of 4H-SiC

Threading dislocations (TDs) are inclined from the [0001] c-axis in 4H-SiC epilayers which are produced by the step-controlled technique. The reason for this inclination is discussed in the framework of isotropic elastic theory of dislocation. The elastic strain energy of a TD in an epilayer is calculated as a function of its orientation, and the minimum energy orientation is used to predict the inclination angle. The results of the calculations are as follows. For a cut-off angle (α) of 4°, a threading edge dislocation (TED) and a threading pure screw dislocation (TpSD) are inclined from the c-axis by 12 and 2°, respectively: Threading near screw dislocations (TnSDs) and threading mixed dislocations (TMDs) are inclined by angles ranging from 8 to 15° from the c-axis, depending on their actual Burgers vectors. Similarly for α of 8°, a TED and a TpSD are inclined from the c-axis by 21 and 4°, respectively: TnSDs and TMDs are inclined from the c-axis by angles ranging from 7 to 17°. These predictions are in good agreement with experiment.

Multi-level Simulation Study of Crystal Growth and Defect Formation Processes in SiC

The mechanism of layer growth as well as defect formation in the SiC crystal is fundamentally important to derive its appropriate performance. The purpose of the present study is to investigate competitive adsorption properties of growth species on the various 4H-SiC polytype surfaces. Adsorption structure and binding energy of growth species in the experimentally condition on various SiC surfaces were investigated by density functional theory. For the SiC(000-1) and SiC(0001) surfaces, the adsorption energy by DFT follows the orders C > H > Si > SiC2 > Si2C > C2H2. Furthermore, based on the DFT results, amount of adsorption of each species in the experimental pressure condition were evaluated by grand canonical Monte Carlo method. H and Si are main adsorbed species on SiC(0001) and SiC(000-1) surfaces, respectively. The ratio of amount of adsorption of Si to H was depending on the surface structure that might explain different growth rate of the surfaces.