Microstructure and defect investigations of the as-grown and annealed ZnO/Si thin films.

The microstructure and defects of as-grown and annealed ZnO/Si thin films were investigated by high-resolution transmission electron microscopy (HRTEM). The cross-sectional bright-field TEM images showed that the ZnO thin films consisted of columnar grains. The selected-area electron diffraction pattern showed that the ZnO/Si thin film were c-axis oriented and the deviation angle along the ZnO (0001) direction with respect to the growth direction was no more than 5°. The grain boundaries can be classified into three types: low-angle boundaries, boundaries near a 30 deg angle with (10<OVERLINE>1</OVERLINE>0) facet structures and large-angle boundaries. In addition to grain boundary, the as-grown and annealing processing defects were also investigated by HRTEM. The crystal quality of the ZnO/Si thin films can be improved by annealing at 600 °C. However, at too high an annealing temperature of 800 °C, the newly produced processing defects such as three layer stacking fault and double stacking fault were formed. The research was useful for us to find optimal growth conditions to improve ZnO/Si thin film quality. [ABSTRACT FROM AUTHOR]