Abstract
We have studied ultrafast carrier dynamics in oxidized silicon nanocrystals (NCs) and the role that surface-related states play in the various relaxation mechanisms over a broad range of photon excitation energy corresponding to energy levels below and above the direct bandgap of the formed NCs. Transient photoinduced absorption techniques have been employed to investigate the effects of surface-related states on the relaxation dynamics of photogenerated carriers in 2.8 nm oxidized silicon NCs. Independent of the excitation photon energy, non-degenerate measurements reveal several distinct relaxation regions corresponding to relaxation of photoexcited carriers from the initial excited states, the lowest indirect states and the surface-related states. Furthermore, degenerate and non-degenerate measurements at difference excitation fluences reveal a linear dependence of the maximum of the photoinduced absorption (PA) signal and an identical decay, suggesting that Auger recombination does not play a significant role in these nanostructures even for fluence generating up to 20 carriers/NC.
Highlights
Silicon is the basic material of today’s integrated circuit technology
With decreasing photon energy the minimum signal decreases and eventually a positive contribution to the absorption change becomes apparent. This observed complex behavior in the time-resolved data is attributed to state filling (SF) and photoinduced absorption (PA) effects
This mechanism will be observed as a positive change in absorption (PA) with its strength depending on the coupling efficiency and the number of carriers present in the initial coupled energy state
Summary
Silicon is the basic material of today’s integrated circuit technology. one of the major drawbacks of this indirect gap semiconductor is its inability to efficiently emit light. There has been no comprehensive study of the effects of surface-related states on the relaxation mechanisms in oxidized Si-NCs over a broad excitation energy range which covers energy states located below and above the direct critical points of the first Brillouin zone of these structures In view of this lack of information, transient photoinduced absorption measurements have been utilized to investigate and timeresolve the various relaxation mechanisms following photoexcitation in the range of 4.2–3.1 eV, corresponding to direct and indirect (phonon assisted) excitations for 2.8 nm Nanoscale Res Lett (2008) 3:315–320 oxidized Si-NCs. The presence of surface-related states appears to play a crucial role in the fast relaxation dynamics of carriers inhibiting the non-radiative Auger recombination even at excitation fluence that generates 20 carriers/NCs
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