数字模拟法研究坩埚锥角对VGF法GaAs单晶生长的影响

Numerical Simulation Study on Impact of Cone Angle of Crucible on VGF GaAs Monocrystal Growth

坩埚锥角是诱发VGF法GaAs单晶出现孪晶与多晶的重要因素之一,应用数值模拟的方法对其进行了研究与探讨,研究发现,在晶体生长的放肩阶段,坩埚锥角为60°,90°,120°3种情况下,晶体生长的固液界面均凹向熔体,随坩埚锥角α的增大,接触角θ变小,非均匀形核几率增加,易诱发孪晶和多晶。根据热量传输分析,在晶体生长的转肩阶段,随坩埚锥角α的增大,沿轴向传走的热量减小,径向传走的热量增加,增大了径向的温度梯度,造成凹的生长界面,导致三相点处过冷度的增加,也增大了孪晶及多晶产生的几率。而在等径生长部分由于远离了坩埚直径增加的区域,坩埚锥角对成晶率的影响较小。考虑到晶体生长的效率,为获得较长的等径部分,需要设计合适的坩埚锥角。选取了90°的坩埚锥角,模拟及实验均证实这一角度即能有效提高单晶成晶率,又能保证一定的晶体生长效率,并生长出直径4英寸的VGF GaAs单晶。

The cone angle of crucible was one of the important factors that induced the VGF GaAs monocrystal to become twin crystal or polycrystal.The growth of VGF GaAs monocrystal was researched by numerical simulation,the results showed that all the solid liquid interfaces were concave to the liquid in shouldering process when the cone angle of crucible was 60°,90° or 120°.With the cone angle of crucible becoming bigger,the contact angle becoming smaller,the probability of heterogeneous nucleation was increased,twin crystal and poly-crystal was induced occurred.Thus twin crystal or polycrystal was achieved easily.According to the analysis of heat transfer,in transition process,with the cone angle of crucible becoming bigger,the heat transfer along the axial direction was reduced and the heat transfer along the radial direction was increased,so the radial temperature gradient was increased and then the concave interface was achieved,lead to the increase of overcooling at triple point and also the incidence of twin crystal or poly-crystal.In diameter growth process,as the solid-liquid interface was far from the diameter-increasing part of the crucible,the cone angle of crucible affected the single crystal growth very slightly.Considering the efficiency of single crystal growth to achieve much longer diameter part,the appropriate cone angle of crucible was needed.Both of the numerical simulation study and experiment results proved that the 90°cone angle of crucible was the best.It could improve the probability and efficiency of single crystal.Then 4″ GaAs monocrystal was achieved.