Superlattices of Si-rich silicon nitride and Si 3 N 4 are prepared by plasma-enhanced chemical vapor deposition and, subsequently, annealed at 1150 C to form size-controlled Si nanocrystals (Si NCs) embedded in amorphous Si 3 N 4 . Despite well defined structural properties, photoluminescence spectroscopy (PL) reveals inconsistencies with the typically applied model of quantum confined excitons in nitride-embedded Si NCs. Time-resolved PL measurements demonstrate 10 5 times faster time-constants than typical for the indirect band structure of Si NCs. Furthermore, a pure Si 3 N 4 reference sample exhibits a similar PL peak as the Si NC samples. The origin of this luminescence is discussed in detail on the basis of radiative defects and Si 3 N 4 band tail states in combination with optical absorption measurements. The apparent absence of PL from the Si NCs is explained conclusively using electron spin resonance data from the Si/Si 3 N 4 interface defect literature. In addition, the role of Si 3 N 4 valence band tail states as potential hole traps is discussed. Most strikingly, the PL peak blueshift with decreasing NC size, which is often observed in literature and typically attributed to quantum confinement (QC), is identified as optical artifact by transfer matrix method simulations of the PL spectra. Finally, criteria for a critical examination of a potential QC-related origin of the PL from Si 3 N 4 -embedded Si NCs are suggested. V C 2014 AIP Publishing LLC. [http://dx.

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The influence of boron (B)-doping and remote plasma hydrogen passivation on the photoexcited charge carrier recombination in silicon nanocrystal/SiC multilayers was investigated in detail. The samples were prepared by high temperature annealing of amorphous (intrinsic and B-doped) Si1-xCx/SiC superlattices. The photoluminescence (PL) intensity of samples with B-doped silicon rich carbide layers was found to be up to two orders of magnitude larger and spectrally red shifted in comparison with that of the other samples. Hydrogen passivation leads to an additional increase in PL intensities. The PL decay can be described well by a mono-exponential function with a characteristic decay time of a few microseconds. This behavior agrees well with the picture of localized PL centers (surface states) together with the passivation of non-radiative defects by boron. The samples with B-doped SiC layers exhibit an additional PL band in the green spectral region that is quenched by hydrogen passivation. Its origin is attributed to defects due to suppression of crystallization of amorphous SiC layers as a result of B-doping. Measurement of ultrafast transient transmission allowed us to study the initial (picosecond) carrier dynamics. It was found to be dependent of pump intensity and interpreted in terms of multiparticle electron-hole recombination

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We studied the nonlinear transient absorption dynamics in silicon nanocrystals/SiO2 superlattices. A different dependence of the measured dynamics on excitation intensity was observed depending on the relative position of the probe photon energy and the absorption edge of nanocrystals. At low photon energies, the dynamics changed with excitation fluence and the signal was ascribed to excited state absorption. However, at photon energies above the absorption edge, the phonon enhancement of indirect absorption prevails over excited state absorption what is reflected in excitation fluence independent dynamics of transient absorption.