【摘要】 晶体的生长速率关系着晶体质量和生产效率,保证晶体质量的同时,实现较高的生产效率是晶体生长速率优化的主要目标。VGF技术生长晶体时,晶体的生长速率主要取决于控温点的温度及降温速率。在保持加热器控温点不变的情况下,利用数值模拟方法研究了0.9,1.8,3.6mm.h-13个速率下6英寸VGF GaAs单晶的生长,通过对比不同生长速率下温度梯度(均为界面附近晶体中的温度梯度)和固-液界面形状的变化及热应力的分布,得出以下结果:随着晶体生长速率的增加,轴向温度梯度增大的同时,沿径向增加也较快;但由于受氮化硼坩埚轴向较大热导率的影响,晶体边缘轴向温度梯度迅速减小;径向温度梯度在晶体半径70mm处受埚壁的影响均变为负值,晶体中大量的热沿埚壁流失,导致生长边角上翘;生长速率的增加使得界面形状由凸变平转凹,"边界效应"逐渐增强,坩埚与固-液界面的夹角逐渐减小,孪晶和多晶产生的几率增加;通过对比,1.8 mm.h-1生长时晶体界面平坦、中心及边缘处热应力均较小、生长速率较大,确定为此时刻优化的生长速率。更多还原

【Abstract】 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.更多还原