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HL: Halbleiterphysik

HL 50: Quantenpunkte und -dr
ähte: Optische Eigenschaften III

HL 50.6: Vortrag

Freitag, 12. März 2004, 12:15–12:30, H14

Blinking and Bleaching of Individual Silicon Nanocrystals and Nanocrystal Ensembles — •Jörg Martin^1,2, Frank Cichos¹ und Christian von Borczyskowski² — ¹Institut für Physik 123705, TU Chemnitz, 09107 Chemnitz — ²Institut für Physik 122501, TU Chemnitz, 09107 Chemnitz

We present for the first time detailed studies of individual silicon nanocrystals by confocal microscopy. Individual nanocrystals obey narrow emission spectra (150 meV) in the range between 500 nm and 600 nm. The emission of single nanocrystals shows a strong intermittency (so called blinking), which is the consequence of an electron tunneling to surrounding trap states. The blinking process itself obeys a power law statistics, which is equivalent to a non-stationary behavior. Indeed we can show, that characteristic times of the blinking, especially the mean lifetime of dark periods during the blinking are a function of the observation time. This non-stationarity shows up as a bleaching of the ensemble, which we can fully explain by the blinking statistics. In addition, an excitation intensity dependence of the blinking statistics is observed. This intensity dependence is the result of different tunneling mechanisms, such as Auger assisted tunneling, which becomes active or inactive at different excitation intensities. A further consequence of the charge tunneling to trap states in the environment is a delayed luminescence of nanocrystal ensembles, which results from the return of charges from the traps to the nanocrystals conduction band. This delayed luminescence fits well to the observed blinking behavior of individual nanocrystals.