Ion beam doping and defect engineering of ZnO nanowires for photodetection and sensing applications

Abstract

The recent progress in science has led to a transition to the nano-world. Semiconducting systems such as ZnO nanowires have drawn a lot of interest for sensor applications, in particular chemical and biological sensing as well as photodetection. This is due to the astonishing surface-to-volume ratio and high sensitivity of the surface under ambient conditions. However, the integration of in particular ZnO nanowires has one major drawback, namely the persistence of the photoconductivity. Instead of quickly returning to the original level, the conductivity persists for several minutes or even hours after switching off the illumination. This effect, known as persistence of the photoconductivity, strongly depends on the properties of the nanowire surface, the doping and the environment conditions. Therefore, the modification of the surface properties, for example through doping procedure, can induce a change in the photoconductivity properties. Within the frame of this thesis, the effect of introducing a controlled amount of aluminum into the crystal lattice of ZnO by means of ion beam implantation was examined. Although aluminum is known to act in ZnO as n-type donor, the implantation process generates additionally defects within the crystal, which can also influence the electrical and photoconductivity properties of ZnO nanowires. Therefore, additional implantation with argon ions was considered as a reference, in order to separate the effect of defects and the aluminum dopants.