Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 13: Poster 1

HL 13.45: Poster

Monday, March 26, 2007, 15:00–17:30, Poster A

Optical size effects in ultra fine ZnO nanowires — Daniel Stichtenoth¹, Tore Niermann², Pai-Chun Chang³, Chung-Jen Chien³, Jia Grace Lu⁴, and •Carsten Ronning¹ — ¹II. Institute of Physics, University of Göttingen — ²IV. Institute of Physics, University of Göttingen — ³Department of Chemical Engineering, UC Irvine — ⁴Department of Physics, University of South California

ZnO nanowires as one-dimensional materials are expected to display novel and unique physical properties. For the optical properties the origin of these can be (1) the large surface to volume ratio, (2) the waveguiding property of nanowires, and (3) the reduced dimensionality, which results in a quantum confinement. Due to the rather small exciton bohr radius in ZnO the latter effect is expected just for wires with a diameter of less than 5 nm. Here, we present luminescence studies of ZnO nanowires with diameters in the expected range of confinement effects. The nanowires were synthesized using two different techniques and TEM studies show beside excellent crystal quality, diameters between 4 nm and 40 nm. Temperature dependent photoluminescence measurements were carried out on the as grown samples. At low temperatures a feature at 3.366 eV, which can be attributed to surface-bound excitons, dominates the spectra. With increasing temperature we observed emerging of up to four phonon replica of the free excitonic transition which are blue shifted in the case of the ultra fine nanowires. An intense green luminescence as found by other groups could even at room temperature not be observed. We will discuss the obtained results with respect to literature.