Berlin 2008 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 21: Symposium Semiconductor Nanowires

HL 21.5: Invited Talk

Tuesday, February 26, 2008, 17:15–17:45, ER 270

Top-Down and Bottom-Up: Nanophotonics with ZnO and Silica Nanowires — •Tobias Voss — University of Bremen, Bremen, Germany — Harvard University, Cambridge MA, USA

We used tapered silica fibers and silica nanowires fabricated in a top-down process to inject laser light into sub-wavelength ZnO nanowires obtained in a bottom-down approach. This technique allowed us to study the waveguiding properties of individual ZnO nanowires. We found that high-order waveguide modes, which carry a significant fraction of the energy at the wire surface or even outside the wire in the form of evanescent fields, were frequently excited. Finite difference time domain numerical simulations confirmed the experimental observations and provided quantitative estimates for the coupling efficiency.

We also studied femtosecond-pulse excitation of individual ZnO nanowires with 800-nm photons from a femtosecond oscillator (60 fs; 11 MHz; 80 nJ). The large ZnO bandgap of 3.37 eV at room temperature requires multi-photon processes for the excitation of electron-hole pairs in the nanowires. We observed second-harmonic generation and the excitation of blue and green photoluminescence. Part of the light emitted from the nanowire couples into its waveguide mode and is emitted from the far end of the nanowire. By comparing the spectra at the excitation spot and at the far end of the nanowire, we were able to measure the transmission losses of the non-linearly excited ZnO nanowire. We observed a significant local heating of the nanowire at the excitation spot and analyzed the temperature distribution in the nanowire with finite-element simulations.