mechanism of unidirectionally and laterally grown ZnO nanorods arrays on inclined columnar seed layer

초록

In recent years, laterally grown ZnO nanorod structures have been used in semiconductor devices[1, 2]. These applications typically have a metal semiconductor-metal (MSM) structure, where ZnO nanorods are laterally grown to fill gaps of interdigited metal electrodes. Hydrothermal method for growing ZnO nanorods is widely used because it has several advantages: low cost, low temperature synthesis, and simple set-up. For lateral growth it is necessary to form metal blocking layers on the ZnO seed layer to prevent vertical growth. After hydrothermal synthesis, electrical connection between each metal layer as electrode is made by connection or contact of each ZnO nanorod which were grown from both sides of ZnO seed layers. However, the connection of individual ZnO nanorod cannot be controlled well. Therefore, if ZnO nanorods can be grown unidirectionally, electrical connection will be more dense by ZnO nanorods direct connection to metal layer. We previously reported a novel method by which ZnO nanorods are grown laterally and unidirectionally using the metal blocking layer and inclined columnar ZnO seed layer[3]. However, detailed mechanisms for unilateral growth form the inclined columnar seed layer should be more investigated. To explain the mechanism, this paper details the connection between the effect of inclined columnar structures and the morphology of grown ZnO nanorods by controlled growth time. Several papers reported that inclined columnar growth of ZnO seed layer can be formed by oblique deposition[4, 5]. We also observed the inclined columnar structure at high tilt angle of 800. The inclined columnar structure is one of major factors to determine a direction of growing ZnO nanorods. Fig. 1 shows grown ZnO nanorods on the inclined columnar structure which are partially half etched. This result revealed that crystal orientation of ZnO seed layer is tilted by the incident angle of sputtered particles. Obviously, ZnO nanorods tend to elongate from the (002)