Excitons in Si nanocrystals: Confinement and migration effects

J Heitmann, F Muller, L X Yi, M Zacharias, D Kovalev, F Eichhorn

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A detailed analysis of the strong room-temperature photoluminescence (PL) signal of size controlled nc-Si is reported. The size control of nc-Si is realized by evaporation of SiO/SiO2 superlattices and subsequent thermally induced phase separation. By this method the synthesis of completely SiO2 passivated Si nanocrystals with a controlled size is demonstrated. A strong blueshift of the photoluminescence signal from 1.3 to 1.65 eV with decreasing crystal size is observed. Resonant photoluminescence measurements prove the breakdown of the k-conservation rule for nc-Si by showing an increase in the no-phonon transition probability with decreasing crystal size. A no-phonon to phonon assisted transition probability ratio above 1 is detected at 4.5 K. These results confirm quantum confinement as the origin of the investigated luminescence signal. The size dependence of the different luminescence properties and the very high no-phonon transition probability indicate a lower confinement barrier compared to other systems containing nc-Si and additional migration effects of the excitons between the nanocrystals. A separation of quantum confinement and migration effects on the PL signal is possible due to the very narrow size distribution of the nc-Si and detailed time and temperature dependent investigations of the photoluminescence.
Original languageEnglish
JournalPhysical Review B
Issue number19
Publication statusPublished - 2004

Bibliographical note

ID number: ISI:000221961700055


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