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

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 $(7\times10^{15}$- $2\times10^{17}$ cm$^{-2})$ 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