ZnO外延膜与蓝宝石衬底的取向偏差及其弯曲变形

Misorientation and Bending of ZnO Films on Sapphire by X-ray Double Crystal Diffractometry

采用常压MOCVD方法在Al2O3(00.1)衬底上生长出了高质量ZnO单晶薄膜。由ZnO(00.2)面和Al2O3(00.6)面及ZnO(10.2)面和Al2O3(11.6)面X射线双晶ω/2θ衍射曲线的相对峰位,得到ZnO外延膜的晶格常数及外延层和衬底间的取向差异角。结果表明外延层和衬底在应力作用下产生了取向差和晶格畸变,并且取向倾斜方向与衬底的切割倾角方向一致;高温直接生长的样品的取向差比有低温缓冲层样品更大,晶格畸变也更严重。高温直接生长的样品弯曲半径小而应力更大;实验测量的应力值和理论计算的热应力值之间存在差异,原因主要是晶格失配应力的存在。有缓冲层的样品由于能更好地弛豫晶格失配引入的应力,热应力所占整个残余应力的比例相对更大。

The structure characteristics of ZnO thin films epitaxially deposited on two-inch (00.1) sapphire substrate by atmospheric metalorganic chemical vapor deposition (AP-MOCVD) were determined by X-ray double-crystal diffractometry methods. The strained lattice parameters, misorientation, bending radius and stress of ZnO films were estimated. The strained ZnO lattice parameters and misorientation between ZnO film and substrate were attained from a pair of symmetric and asymmetric diffraction,which contain the diffraction peaks of ZnO epilayer and sapphire substrate.The experimental bending radius was determined from the diffe-(rences) of the X-ray rocking curve peak positions move of the different points on ZnO film and experimental stress was calculated from that radius. Theoretical bending radius and residual thermal stress were also calculated,which is caused by the difference in the thermal expansion coefficients between the ZnO layer and sapphire substrate. The result shows that misorientation and lattice distortion were induced in ZnO layer by the actions of thermal and lattice stress. The misorientation azimuth angle is nearly the same with the miscut azimuth of sapphire substrate, which indicates that substrate miscut is one of the key factors of the misorientation,but the misoriention angle is greatly little camparing with the substrate miscut angle. Comparing to the direct-growing film, the sample with a low-temperature buffer layer has less misorientation angle and lattice stress. Meanwhile, the experimental bending radius of the sample with a low-temperature buffer layer is smaller than that of the direct-growing sample and residual thermal stress is relatively bigger. That means the low-temperature buf-(fer ) layer is of great benefit to reduce the misoriention and lattice distortion of ZnO films on Al_2O_3 and enhance the quality of ZnO film.