Electronic transport in superlattice-structured ZnO Nanohelix.

Superlattice-structured ZnO nanohelix is a structure that is made of a coiling nanobelt, which is composed of ZnO nanostripes oriented alternatively in two different orientations (Science 2005, 309, 1700). The nanostripes run almost in parallel to the nanobelt direction but at an offset angle of approximately 5 degrees . We have measured the transport properties of a nanohelix and found its abnormal nonlinear characteristic. In comparison to the Ohmic transport property of a single crystal ZnO nanobelt measured under the same experimental conditions, the symmetric "Schottky-type" I-V property of the nanohelix is suggested due to nanostripe boundaries and surfaces, where built-in periodic back-to-back energy barriers might occur across the nanostripe interfaces as a result of polar charges and interface-strain-induced piezoelectric effect. The effective potential barrier across the nanostripe boundary is estimated to be approximately 24 meV. With the increasing of bias voltage, electrons can effectively tunnel through and thermionic emission across nanostripe boundaries, leading to a fast increase in transport current. It is suggested that the ZnO nanohelix could form a new type of band structure modulated superlattice for fabricating novel electronic devices.