• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.272-278
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• 2013

In this study, a c-axis displacement and an internal stress of the sapphire crystal of 300 mm length have been analyzed numerically and the crystal length having no sub-grain defects have been predicted. The hot zone structures were modified with the crucible geometry change and the additional insulation layer installed above the crucible. The simulation results show that the c-axis displacement difference between the original hot zone and others originated from the sub-grain defect formations in the sapphire ingot. When the crystal grown by CZ (Czochralski) grower using the modified hot zone, the crystal length having no sub-grain defects was increased about 57 mm maximum than the original one. When the simulation results compared with the experimental one, the predicted crystal length having no sub-grain defects were well corresponded with the experiment one in c-axis wafer of the 300 mm sapphire ingot. Therefore the sapphire crystal of 250 mm length having no sub-grain defects was successfully grown by CZ process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.265-271
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• 2013

Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal for LED application. In this study, the inductively-heated CZ growth processes for the sapphire crystal of 300 mm length have been analyzed numerically using finite element method. The hot zone structures were modified with the crucible geometry change and the additional insulation layer installed above the crucible. The results show that the solid-liquid interface height decreased from about 80 mm at initial stage to 40 mm after mid-stage due to achieve the growth speed balance. Also the optimal input power of the modified system was similar with the original one due to the compensation effects of the crucible geometry and additional insulation. The crystal temperature grown by the modified CZ grower was increased about 10 K than the original one. Therefore the sapphire crystal of 300 mm height was grown successfully.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.1
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• pp.83-91
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• 1994

We have constructed a vertical gradient freeze (VGF) grower for GaAs single crystals 2 inch in diameter and have grown semi-insulating GaAs co-doped with Cr and In. For the co-doped crystal, the segregation coefficients of the dopants remain unchanged when compared to those doped with only Cr or In. The concentration of Cr and in atoms range from about $2{\Times}10_{16} to 3{imes}10^{17} cm^{-3}$ and $2{\Times}10^{19} to 3{\Times}10^{20} cm^{-3}$ at the seed to the tail part of the grown crystal, respectively. The averaged dislocation etch pit density is found to be less than $8000 cm^{-2}$ throughout the ingot. It is also found that there is some evidence of lattice hardening for the crystal in which the dislocation density is decreased to less than $1000 cm^{-2}$ as In concentration increases. The resistivity increases abruptly from $10^{-2}$ up to $10^8$ Ohm-cm, while the carrier concentration decreases from $10^{16}$ to $10^8 cm^{-3}$ along the growth direction of the GaAs crystal. Semi-insulating properties can be obtained above a critical concentration of Cr of about $6{\Times}10{^16} cm^{-3}$ in the crystal. The main deep levels existing in the GaAs: Cr,In sample are two electron traps at $E_C-0.81eV, E_C-0.35eV$, and two hole traps at $E_V+0.89eV, E_V+0.65eV$.