MATERIAL STRENGTH STUDY ON GROWTH OF HIGH QUALITY BULK SINGLE CRYSTALS FOR ELECTRONIC/OPTICAL DEVICES

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1. A computer code was developed for for evaluating the dislocation density of Si, GaAs and InP bulk single crystals during the Czochralski growth using a dislocation kinetics model called the Haasen-Sumino model. The following are the research results obtained from the analyzes using this computer code. (1) The rate of dislocation multiplication is faster in the order of GaAs, InP and Si. Even in the case of Si, the dislocation density reaches a steady state value within a few seconds, and InP and GaAs have faster rate of dislocation multiplication by more than a hundred times and a thousand times, respectively. (2) InP and GaAs have larger dislocation density at a steady state than Si. (3) A continuous simulation for the CZ growth process gives a W-type distribution of dislocation density along a diameter of a bulk single crystal, which is observed in a real bulk single crystal. This verifies the computer simulation.2. The following are results of the research on the relation between … More the thermal stress during the growth of a LiNbO_3 (LN) single crystal and its quality. (1) Thermal stress is higher in the a-axis pulling than in the c-axis pulling. This verifies the empirical fact that cracking is easier to occur in the a-axis pulling than in the c-axis pulling. (2) According to the thermal stress analysis, a single crystal grown in the a-axis direction has a wider region of low thermal stress in its internal part than a single crystal grown in the c-axis direction. This implies that the a-axis pulling gives a bulk single crystal with higher quality than the c-axis pulling. The examination of the quality of single crystals with the x-ray topograph reveals high quality of a single crystal grown in the a-axis pulling which has fewer subgrains than a single crystal grown in the c-axis direction. It is shown that the results of the thermal stress analysis give effective information on the growth method of a single crystal with high quality. (3) Failure of a LN Single crystal due to thermal stress occurs at the cleavage planes and may be dominated by the tensile stress normal to the cleavage planes. The failure stress shows the Weibull distribution. Less