Feb 25, 2008
Quantum dot-like emission from ZnO nanowire quantum-wells
Ensembles of narrow cathodoluminescence peaks were detected when exciting MgZnO/ZnO quantum-wells grown on top of ZnO nanowires. ZnO nano-quantum-wells are regarded as important building blocks for future optoelectronic devices in the ultraviolet spectral range, including LEDs and lasers. The quantum-dot like behavior of MgZnO/ZnO heterostructures on the tip of ZnO nanowires enables the use of enhanced quantum confinement effects and localized excitons that are stable at room temperature. Further work will be devoted to the creation of a few or single quantum-dot emitters at the tip of ZnO nanowires, possibly operating at room temperature, as a light source for quantum communication.
MgZnO/ZnO quantum-wells have successfully been grown on top of ZnO nanowires by pulsed laser deposition (PLD). Optical spectroscopy of light emission from single nanowire quantum-wells confirmed the growth of MgZnO barriers and the ZnO quantum-well. Interestingly, sharp emission features were observed from the quantum-well band of the spectra. By using high resolution transmission electron microscopy, nanometer-sized ZnO material flucuations in the MgZnO barrier could be identified as a physical origin of the sharp lines, an important step towards the incorporation of quantum dots into ZnO nanowires. Furthermore, the number of sharp peaks increased with increasing excitation intensity observed by photoluminescence spectroscopy of single wires, clearly indicating quantum dot-like behaviour of the nanowire quantum-well structures.
For growth of the nano-quantum-well structures, the high-pressure PLD process for the fabrication of ZnO nanowires was combined with the low-pressure PLD growth of quantum wells, either performed in the same vacuum chamber (in situ) or in two different PLD systems (ex situ).
The results give a deeper insight into the correlation between structural and optical properties of advanced ZnO nano-quantum-well structures. Growth of ZnO nano-quantum-dots can be envisioned in the near future.
About the author
The authors work together in the specific targeted research or innovation project (STReP) Nanophotonic and Nanoelectronic Devices from Oxide Semiconductors (NANDOS) funded by the EU under contract No. FP6-016924. Researchers from the CEA-CNRS group “Nanophysique et Semiconducteurs” (headed by Daniel Le Si Dang), Grenoble, France, the Semiconductor Physics Group (Marius Grundmann), University of Leipzig, Germany, and the National Center of Scientific Research Demokritos (Anastasios Travlos), Greece, were involved in the work. The main part of the work was performed by PhD student Christian Czekalla, who is involved in growth and optical characterization in Leipzig and Grenoble. More detailed information about the coauthors and NANDOS can be found on the websites of the involved groups and of the NANDOS project.