Transition from silicon nanowires to isolated quantum dots: Optical and structural evolution

Abstract

The evolution of the structural and optical properties of a silicon core in oxidized nanowalls is investigated as a function of oxidation time. The same individual nanostructures are characterized after every oxidation step in a scanning electron microscope and by low-temperature photoluminescence, while a representative sample is also imaged in a transmission electron microscope. Analysis of a large number of recorded single-dot spectra and micrographs allows to identify delocalized and localized exciton emission from a nanowire as well as confined exciton emission of a nanocrystal. It is shown how structural transitions from one-to zero-dimensional confinement affect single-nanostructure optical fingerprints.

Biexciton Emission as a Probe of Auger Recombination in Individual Silicon Nanocrystals

“…Finally, space-separated silicon nanocrystals were formed by shrinking the core size of the nanowalls via self-limiting oxidation 31 at 900°C for 5 h, forming a thick oxide shell (tens of nanometers). In contrast with the previous samples, the luminescence fwhm here was found to be broad, approximately 100−200 meV at room temperature and ∼1 meV at 10 K. 32 Previously, all three samples were optically analyzed using standard techniques and the crystallinity of the silicon nanoparticles was confirmed by TEM. 4,30 The insets in Figure 2 are typical TEM images of silicon nanocrystals from HSQ (left) and SOI (right) samples, where (111) plane lattice fringes of crystalline silicon and a few-nanometer thick amorphous oxide layer for the SOI sample are visible.…”

Direct Bandgap Silicon: Tensile‐Strained Silicon Nanocrystals

“…This value varies from one nanocrystal to another, see the histogram in Figure f, and it typically amounts to ℏΩ = (49 ± 3) meV. This is much less than the bulk value of the momentum‐conserving TO phonon (57 meV), as well as than the value of TO phonon manifesting itself in the luminescence of silicon‐oxide‐capped SiNcs (60–62 meV).…”

Rapid Trapping as the Origin of Nonradiative Recombination in Semiconductor Nanocrystals

“…Although at 300 K the decay can be well-fitted by a monoexponential function, at low temperatures a biexponential decay becomes apparent. The temperature dependence of the NP-line width 37 and its peak position, as well as the clear presence of material-specific phonon replicas 38 strongly indicate emission from quantum-confined excitons in silicon: only the measured particles satisfying these stringent requirements were considered as single Si-NCs in our study. Indeed, if we exclude the unlikely event of two distinct and adjacent Si-NCs emitting at the same energy, the temperature evolution of the PL spectrum should reveal two narrow NP emission lines at low temperatures when two different adjacent emitters are measured.…”