LiNbO_3晶体小面生长动力学的实验研究

EXPERIMENTAL STUDY ON FACET GROWTH DYNAMICS IN LiNbO_3

按同成分配比的ＬｉＮｂＯ３的原料中，掺入溶质钇，用提拉法生长晶体时，人为地引入生长层，生长层记录了不同时刻的生长界面形态，借以追溯生长过程中固－液界面的形态和演变过程。晶体沿Ｙ轴生长，ＬｉＮｂＯ３晶体形成小面的｛０１１２｝面族中的（０１１２）面与生长轴的夹角最小，它与凸的固－液界面相切时，形成小面生长区。利用“倾倒法”使晶体和熔体快速分离，在晶体底部观察到平坦的（０１１２）面小面生长区。通过不同的晶体截面，观察了晶体内（０１１２）面小面生长区的形态。测量了小面半径与相应的固－液界面的曲率半径。结果表明：小面半径的平方与相应的固－液界面的曲面的曲率半径成比例，这一结果与小面生长的动力学理论预言的结论相一致。最后讨论了小面生长机制，计算了小面生长比非小面生长所需要增加的过冷度。

facet growth is a phenomenon often observed in crystal growth of semiconductors and oxides by Czochralski method. Brice wad the first to explain the kinetics of the facet formation. If the solid-liqued interface is non-singular, the growth mechanism follows a linear law, v= A0 T0. A given growth rate requires a certain supercooling aT,' A, is a kinetic coefficient. Therefore the solid-liquid interface is isothermal. If there is a singular face on the solidliquid interface, this singular face will deviates from the curved solidunliquid interface because the growth mechanism of the singular face is different form that of the non--singular face. Thus a planar facet growth section appears. In order to study the evolution of the solid-liquid interface during the growth process, growth striations, which record the morphology of the growth interface at different instant, can be used. In this paper, growth striations are introduced into LiNbO3 crystals grown by Czochralski method from congruent melts doped with yttrium. The crystals are grown along the y axis. The growth rate is 4--6mm/hour, the rotational rate is 8-13cycles/minute. After the oriented crystal was polished and etched with a 1: 2 mixture of hydrofluoric acid and nitric acid, the pattern of ferroelectric domains can be observed directly by optical microscope. Since in LiNbO3 crystal, it was demonstrated that there exists a one-to-one correspondence between the ferroelectric domains and the growth striations, the configuration of the domains reveals the evolution of solid-liquid interface during growth process. In our experiments, the facet growth section was found on the solid-liquid interface which was identified as (0112) plane. The morphology of the facet was inspected on the z-cross section as well as on the y-cross section. The facet radius and the radius of curvature of the solidliquid interface were measured. It was shown that the square of the facet radius is proportional to the radius of curvature of the solid-liquid interface, which is in good agreement with the theory of the facet growth dynamics. The mechanism of facet growth was discussed and the additional supercooling needed for the facet growth was deduced from the experiment.