Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 44: Poster Session: Quantum Dots and Wires - Transport & Optical Properties

HL 44.8: Poster

Dienstag, 27. März 2012, 09:30–12:30, Poster D

Persistent conductivity in ZnO nanowires in different gas atmospheres — •Davide Cammi, Irma Slowik, Raphael Niepelt, Andreas Johannes, and Carsten Ronning — Institute of Solid State Physics, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 Jena, Germany

Nanostructures of ZnO, due to the high surface to volume ratio, show a strong persistent photoconductivity (PPC). The current induced by above gap illumination persists for a long time after switching off of the excitation, compared to the typical lifetime of photogenerated carriers in the bulk. This effect is based on the up-ward band bending induced by the adsorption of oxidizing molecules at the surface, like oxygen, present in the ambient. The built-in potential tends to separate free electrons and holes generated by the optical irradiation, increasing their lifetime. PPC considerably influences the properties of nanostructure based devices for optoelectronic applications or chemical and biochemical sensors. We compare the PPC observed in untreated and treated ZnO nanowires with different coating layers, which should passivate the surface, reducing the band bending and correspondingly the persistence of the photoconductivity. Furthermore, the influence of hydrogen plasma treatment is presented. We exposed nanowires to different atmospheres, performing measurements in synthetic air (oxygen-rich), nitrogen, carbon dioxide and air, studying the effect of different pressures. A model is proposed to explain the different observed decay rates of the current depending on the chemical species present in the ambient and on the treatment of the surface.