蓝宝石基片的处理方法对ZnO薄膜生长行为的影响

Effect of sapphire substrate pre-treatment on the growth of ZnO films

采用反应射频磁控溅射方法,在经过不同方法处理的蓝宝石基片上,在同一条件下沉积了ZnO薄膜.利用原子力显微镜、X射线衍射、反射式高能电子衍射等分析技术,对基片和薄膜的结构、表面形貌进行了系统表征.研究结果显示,不同退火条件下的蓝宝石基片表面结构之间没有本质的差异,均为α-Al2O3(001)晶面,但基片表面形貌的变化较大.在不同方法处理的蓝宝石基片上生长的ZnO薄膜均具有高c轴取向的织构特征,但薄膜的表面形貌差异较大.基片经真空退火处理后,ZnO薄膜的生长形貌与基片未处理时十分类似,具有+c取向和-c取向两种外延岛特征;基片经氮气环境退火后,ZnO薄膜的生长形貌具有单一的-c取向外延岛特征,晶粒尺寸较大,但薄膜表面粗糙度没有明显改善;基片经氧气环境退火后,ZnO薄膜的生长形貌仍为-c取向外延岛特征,薄膜表面粗糙度显著降低.对于未处理、真空退火、氮气退火和氧气退火等方法处理的蓝宝石基片ZnO薄膜表面形貌的自仿射关联长度分别为619,840,882和500nm.

Using the reactive radio-frequent magnetron sputtering method, ZnO thin films were deposited on pretreated （100） sapphire substrates. The effect of substrate pretreatments on the growth of ZnO films was studied with the structural and morphological characterization using atomic force microscopy, reflection high-energy electron diffraction and X-ray diffraction. It was found that both the original substrate and the substrates annealed in vacuum （8×10^-4 Pa）, nitrogen atmosphere （40 Pa）, and oxygen atmosphere （40 Pa） at 750℃ for 4 h have the same surface structure that can be indexed to be α-Al2O3 （001）. The surface morphologies of the substrates are different from each other. All the ZnO films grown on the substrates are highly c-axis textured. Their morphologies, however, are related to the pretreatment. For the substrate annealed in vacuum, the film has the morphology with - c and ＋ c epitaxial islands, similar to ZnO grown on the untreated substrate. For the substrate annealed in nitrogen, the film has the morphology with only - c epitaxial islands and has quite large grains and surface roughness. For the substrate annealed in oxygen, the films also has the morphology with - c epitaxial islands, but the surface is much smoother. The surface roughness is as small as 1.5 nm.