Ding G.,General Research Institute for Nonferrous Metals, China |
Ding G.,Guojing Infrared Optical Technology Co. |
Tu H.,General Research Institute for Nonferrous Metals, China |
Su X.,General Research Institute for Nonferrous Metals, China |
And 7 more authors.
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2011
The crystal growth rate was critical to the quality and production efficiency. The optimization aimed at to achieve higher production efficiency and to ensure the quality. In VGF crystal growth procedure, the crystal growth rate depended on the temperature at control point and the cooling rate. The 6 inch VGF-GaAs crystal grown was studied at rates of 0.9, 1.8, and 3.6 mm·h -1 respectively with the aid of numerical simulation. By comparing the temperature gradient, the interface shape and the thermal stress distribution in the crystals grown at those rates, some results were presented: Increasing crystal growth rate, the axial temperature gradient was increased, and the accretion along radius was also faster. Because of the effect of higher heat conductivity of BN crucible along the wall, the axial temperature gradient decreased quickly at the edge of crystal, also the radial temperature gradients in the crystal grown at different rates became minus after 70 mm along radius. Large amount of heat flux flew out along the crucible wall and lead the crystal growth edge and corner upturned. As the growth rate increasing, the interface shape changed from convex to flatness and concave, 'interface effect' was strengthened, the angle between interface and crucible wall became smaller and the incidence of twin and polycrystalline increased. It was found that the crystal interface with growth rate of 1.8 mm·h -1 was flat, the thermal stress at the center and edge were lower, and the production efficiency was bigger, so the optimized growth rate was determined to be 1.8 mm·h -1.