外延生长的SrTiO_3/DyScO_3薄膜的微结构研究

Dislocation in SrTiO_3 Film Grown on DyScO_3 by Pulse Laser Ablation

利用激光分子束外延技术在DyScO3（DSO）衬底上异质外延生长了SrTiO3（STO）薄膜.采用原位X射线衍射方法在20~300 K范围内测量了低温下薄膜的热膨胀系数;讨论了应变与晶格失配之间的关系.薄膜的晶格参数在80 K的异常变化可能预示着结构相变的存在.高分辨X射线衍射用来分析样品中存在的两种位错：剪切位错和螺旋位错.结果显示,总的螺旋位错密度要比剪切位错密度大得多.我们认为螺旋位错是样品生长过程中的主要缺陷;剪切位错密度随着样品厚度的增加而增加.这两种位错密度之间的比例关系决定了薄膜的生长模式.

SrTiO3 （STO） films are fabricated on DyScO3 （DSO） substrates by pulse laser deposition. In-situ X-ray diffraction （XRD） at the temperature range of 20 - 300 K is used to characterize the thermal expansion coefficient at low temperature. The lattice mismatch dependence of temperature between STO film and the substrate is also determined. The abnormal behavior in lattice parameter at 80 K may be the hint of a phase transition. High resolution XRD is performed to detect the distribution of two kinds of dislocations, i.e., screw and shear. Results show that the density of total screw dislocation is much larger than the shear one. We believe that the screw dislocation is the main defects formed at the beginning of the film growth. Shear dislocation increases with the increase of the film thickness. We argue that the ratio between these two dislocations results in the growth mode of the film.