Hamburg 2001 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 16: Quantenpunkte und -dr
ähte: Optische Eigenschaften I
HL 16.7: Vortrag
Dienstag, 27. März 2001, 12:00–12:15, S2
Optical Properties of ZnO nanocrystals — •Huijuan Zhou1, Helder R. Alves1, Detlev M. Hofmann1, Bruno K. Meyer1, Georg Kaczmarczyk2, and Axel Hoffmann2 — 1I. Physics Institute, Justus-Liebig-University Giessen — 2Institute of Solid State Physics, Technical University of Berlin
ZnO nanocrystals are matter of interest due to various reasons, such as sensor applications or near-UV emitters due to its large bandgap. However, excitonic emission from ZnO nanocrystals was rarely reported up to date. We prepared ZnO nanocrystals by the precipitation of Zn2+ and OH− in an alcoholic solution containing sodium-hexametaphosphate. After washing and drying the nanocrystals were obtained as atable free-standing powders. The nanocrystal size was determined by X-ray scattering and absorption experiments. It increases from 4.3 nm to 7 nm with increasing annealing temperature (150 oC to 500 oC). For all samples two emission bands were observed, one broad band at about 2.2 eV and the excitonic recombination. The two bands redshifted upon annealing and the excitonic emission dominates for annealing temperatures above 300 oC. The 2.2 eV band can be related to the presence of OH− on the nanocrystal surface as observed by Raman spectroscopy. A third emission becomes observable in the annealed samples we tentatively ascribe it to oxygen deficiency defects similar to the green band in bulk ZnO crystals. the results show that surface passivation plays a cruicial role for the emission properties of the nanocrystals.