An experimental study of the temperature dependence of photoluminescence time decay in size-controlled silicon
nanocrystals in silicon nanocrystal/SiO2 superlattices is reported. The samples were prepared using thermal
evaporation and subsequent thermally induced phase separation. The slow (microseconds) decay line shape is
described well by a stretched exponential. The temperature dependence of the photoluminescence dynamics
can be understood in terms of thermal activation of recombination processes, including hopping of carriers
between localized states. Additional hydrogen treatment causes an increase in both parameters of the stretched
exponential function. This behavior is interpreted as a consequence of H2-passivation of dangling bonds defects.
We review results we obtained by nonlinear time-resolved laser spectroscopy of silicon nanocrystals. The results of
photoluminescence measurements on the femtosecond to microsecond time scales and of the picosecond pump and probe
absorption measurements indicate the important role of carrier trapping into nanocrystals surface states and of Auger
process in photoexcited carrier relaxation and recombination. The optical response of assemblies of silicon nanocrystals
was found to be strongly dependent on the wavelength of the excitation light. The relation between microscopic carrier
processes and optical nonlinear properties of the material as well as the impact on possible development of silicon laser
are discussed.
The progress of laser technology during the past twenty years made it possible to extend the time resolution of optical
experiments down to picosecond and femtosecond time scales. In this paper, the state-of-the-art techniques of ultrafast
optical spectroscopy are reviewed. It is shown, how these can be used to monitor directly dynamics of elementary
excitations in semiconductor nanocrystals and how, in turn, understanding ultrafast carrier processes makes it possible to
tailor the properties of these structures for application in photonics, nanoelectronics and spintronics.
We have studied the temporal response of four-wave mixing in
silicon to study the coherence of picosecond pulses and the diffusion of free carriers. The measurements were done at room temperature. The sample used was an N-type monocrystalline silicon
with the impurity density of 5 1O15 cm-3.
Conference Committee Involvement (1)
23rd Slovak-Czech-Polish Optical Conference on Wave and Quantum Aspects of Contemporary Optics
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