Yb∶Ca_5(PO_4)_3F激光晶体的生长缺陷

GROWTH DEFECTS OF Yb∶Ca_5(PO_4)_3F LASER CRYSTAL

采用提拉法生长了质量优异的Yb∶Ca5(PO4)3F(Yb∶FAP)晶体。运用化学腐蚀,光学显微镜、扫描电子显微镜以及能量散射光谱仪观察了该晶体中的生长条纹和包裹物等宏观缺陷,以及晶体的位错腐蚀形貌、位错密度及其分布情况,同时观察了晶体中亚晶界的形态。由晶体中位错的径向变化以及生长条纹可知:晶体在生长过程中为微凸界面生长。高温下CaF2的挥发造成了在晶体生长后期熔体中组分偏离化学计量比,出现组分过冷,形成包裹物,且位错密度显著增加。Yb∶FAP晶体的各向异性使得晶体在(10 10)面的位错蚀坑形状、大小以及深度不同,而(0001)面的位错蚀坑呈规则的六边形;这也是晶体中形成亚晶界结构的主要原因。讨论了减少晶体中缺陷的一些方法。

Yb ： Ca5 （PO4）3 F（Yb ： FAP） crystal of high quality was grown by the Czochralski method. The macro defects in crystals obtained, including growth striation, inclusions, dislocations, and sub grain boundary were observed by chemical corrosion, Leitz optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. The dislocation density of radial distribution and growth striation of Yb ： FAP crystal reveal that the growth of crystal is on a convex solid-liquid inter face. The volatilization of CaF2 at a high temperature causes the deviation in composition from the stoichiometry, which results in the formation of inclusions and an increase in the dislocation density. The shapes of etch pits located on the （0001） plane exhibit a hexagonal structure, whereas the shapes, sizes and lengtbs of etch pits of dislocations on the （10 10） face are different due to the cryslal anisotropy of Yb ： FAP crystal, which is the main reason for the formation of a sub grain boundary in Yh ： FAP crystal. The methods of reducing the defects were also discussed.