11 research outputs found
A silicon nanocrystal/polymer nanocomposite as a down-conversion layer in organic and hybrid solar cells
Impact of AFM-induced nano-pits in a-Si:H films on silicon crystal growth
Conductive tips in atomic force microscopy (AFM) can be used to localize field-enhanced metal-induced solid-phase crystallization (FE-MISPC) of amorphous silicon (a-Si:H) at room temperature down to nanoscale dimensions. In this article, the authors show that such local modifications can be used to selectively induce further localized growth of silicon nanocrystals. First, a-Si:H films by plasma-enhanced chemical vapor deposition on nickel/glass substrates are prepared. After the FE-MISPC process, yielding both conductive and non-conductive nano-pits in the films, the second silicon layer at the boundary condition of amorphous and microcrystalline growth is deposited. Comparing AFM morphology and current-sensing AFM data on the first and second layers, it is observed that the second deposition changes the morphology and increases the local conductivity of FE-MISPC-induced pits by up to an order of magnitude irrespective of their prior conductivity. This is attributed to the silicon nanocrystals (<100 nm) that tend to nucleate and grow inside the pits. This is also supported by micro-Raman spectroscopy
Light amplification due to free and localized exciton states in ZnCdSe GRINSCH structures
International audienceIn this paper we present measurements of light amplification in optically pumped ZnCdSe GRINSCH (graded refraction index separate confinement heterostructures), In several differently designed samples we observe the presence of two gain mechanisms, which involve localized excitons and exciton-exciton inelastic scattering processes, respectively. The influence of the GRINSCH sample structure on gain is discussed in terms of their improved light-guiding properties
Electric-field-enhanced metal-induced crystallization of hydrogenated amorphous silicon at room temperature
Determination of light amplification processes in MOCVD grown ZnCdSe GRINSCH structures
International audienceIn this paper we present measurements of light amplification in optically pumped ZnCdSe graded refraction index separate confinement heterostructures (GRINSCH). In several differently designed samples we observe the presence of two gain mechanisms, which involve localized excitons and exciton-exciton inelastic scattering processes, respectively, The influence of the GRINSCH structure on gain is discussed with respect to light guiding variations due to sample design. A numerical simulation is used to investigate the phenomenon of gain quenching with decreasing barrier width
Temperature behaviour of optical properties of Si
Silicon nanocrystals were prepared by Si+-ion implantation and subsequent
annealing of SiO2 films thermally grown on a c-Si wafer. Different implantation
energies (20-150 keV) and doses - cm were used
in order to achieve flat implantation profiles (through the thickness of about 100 nm)
with a peak concentration of Si atoms of 5, 7, 10 and 15 atomic% . The presence of
Si nanocrystals was verified by transmission electron microscopy. The samples
exhibit strong visible/IR photoluminescence (PL) with decay time of the order of
tens of μs at room temperature. The changes of PL in the range 70-300 K can be
well explained by the exciton singlet-triplet splitting model. We show that all
PL characteristics (efficiency, dynamics, temperature dependence, excitation
spectra) of our Si+-implanted SiO2 films bear close resemblance to those of a
light-emitting porous Si and therefore we suppose similar PL origin in both
materials