BaTiO_3铁电薄膜低温异质外延的生长模式研究

Study of growth mode in BaTiO_3 heteroepitaxy at low temperature

利用激光分子束外延异质外延BaTiO3薄膜.通过反射式高能电子衍射对薄膜生长进行原位监测,利用原子力显微镜分析薄膜表面形貌,发现在沉积速率为0.016nm/s,激光功率为6J/cm2的条件下,当基片加热温度高于480℃时,BaTiO3薄膜以层状生长模式进行生长;而当温度在430～480℃之间时,薄膜生长为SK模式,即层状加岛状的混合生长模式.进一步降低基片加热温度,在430℃以下观察到了三维岛状生长模式.通过优化激光功率和沉积速率等工艺参数,得到了层状生长BaTiO3薄膜的最低结晶温度为330℃.根据实验结果分析了激光功率对薄膜生长温度的影响.同时结合X射线衍射分析在不同的生长条件下,研究温度对薄膜异质外延生长的影响,发现在较高的生长温度下,在BaTiO3薄膜生长过程中,位错产生的几率较小,薄膜的外延性好,而在较低的生长温度下,薄膜内部位错较多,异质外延性不佳.

BaTiO3 thin films were grown by laser molecular beam epitaxy. The growth mode was determined by in-situ reflective high energy electron diffraction, and the surface of the films was studied by ex-situ atomic force microscopy. At the deposition rate of 0.016 nm/s and the laser energy density of 6 J/cm2, layer-by-layer growth was observed above 480°C substrate temperature, while the Stranski-Krastanov growth mode, that was layer-by-layer growth plus island growth mode, prevailed between 480°C and 430°C. On further decreasing the substrate temperature, the island growth was determined under 430°C. With the optimization of deposition process in terms of laser energy density and deposition rate, the lowest crystallization temperatures of SrTiO3 films grown in layer-by-layer growth mode were obtained as low as 380°C. The effects of laser energy density on growth temperature were studied. Combining the X-ray diffraction patterns, the effects of growth temperature to the heteroepitaxy were also discussed.