Influence of the threading dislocations on the electrical properties in epitaxial ZnO thin films

The structural and electrical properties of epitaxial ZnO films grown by pulsed-laser deposition on sapphire (0 0 0 1) were investigated by high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), scanning capacitance microscopy (SCM), conductive atomic force microscopy (C-AFM), and transmission electron microscopy (TEM). The results of XRD and AFM revealed that the ZnO films have a columnar-grain structure consisting of epitaxial cores surrounded by annular boundaries. The core and boundary regions exhibited significantly different capacitive responses and field emission current. The results of TEM indicated that the annular boundaries have high-density edge threading dislocations. The shift of flatband voltage and the raise of potential barrier at the boundaries observed by SCM and C-AFM were attributed to the interface trap densities caused by the existence of high-density edge threading dislocations.