Structure, morphology, and photoluminescence of porous Si nanowires: effect of different chemical treatments

The structure and light-emitting properties of Si nanowires (SiNWs) fabricated by a single-step metal-assisted chemical etching (MACE) process on highly boron-doped Si were investigated after different chemical treatments. The Si nanowires that result from the etching of a highly doped p-type Si wafer by MACE are fully porous, and as a result, they show intense photoluminescence (PL) at room temperature, the characteristics of which depend on the surface passivation of the Si nanocrystals composing the nanowires. SiNWs with a hydrogen-terminated nanostructured surface resulting from a chemical treatment with a hydrofluoric acid (HF) solution show red PL, the maximum of which is blueshifted when the samples are further chemically oxidized in a piranha solution. This blueshift of PL is attributed to localized states at the Si/SiO(2) interface at the shell of Si nanocrystals composing the porous SiNWs, which induce an important pinning of the electronic bandgap of the Si material and are involved in the recombination mechanism. After a sequence of HF/piranha/HF treatment, the SiNWs are almost fully dissolved in the chemical solution, which is indicative of their fully porous structure, verified also by transmission electron microscopy investigations. It was also found that a continuous porous Si layer is formed underneath the SiNWs during the MACE process, the thickness of which increases with the increase of etching time. This supports the idea that porous Si formation precedes nanowire formation. The origin of this effect is the increased etching rate at sites with high dopant concentration in the highly doped Si material

Porous anodic alumina on galvanically grown PtSi layer for application in template-assisted Si nanowire growth

We report on the fabrication and morphology/structural characterization of a porous anodic alumina (PAA)/PtSi nano-template for use as matrix in template-assisted Si nanowire growth on a Si substrate. The PtSi layer was formed by electroless deposition from an aqueous solution containing the metal salt and HF, while the PAA membrane by anodizing an Al film deposited on the PtSi layer. The morphology and structure of the PtSi layer and of the alumina membrane on top were studied by Scanning and High Resolution Transmission Electron Microscopies (SEM, HRTEM). Cross sectional HRTEM images combined with electron diffraction (ED) were used to characterize the different interfaces between Si, PtSi and porous anodic alumina

Lateral electrical transport, optical properties and photocurrent measurements in two-dimensional arrays of silicon nanocrystals embedded in SiO2

In this study we investigate the electronic transport, the optical properties, and photocurrent in two-dimensional arrays of silicon nanocrystals (Si NCs) embedded in silicon dioxide, grown on quartz and having sizes in the range between less than 2 and 20 nm. Electronic transport is determined by the collective effect of Coulomb blockade gaps in the Si NCs. Absorption spectra show the well-known upshift of the energy bandgap with decreasing NC size. Photocurrent follows the absorption spectra confirming that it is composed of photo-generated carriers within the Si NCs. In films containing Si NCs with sizes less than 2 nm, strong quantum confinement and exciton localization are observed, resulting in light emission and absence of photocurrent. Our results show that Si NCs are useful building blocks of photovoltaic devices for use as better absorbers than bulk Si in the visible and ultraviolet spectral range. However, when strong quantum confinement effects come into play, carrier transport is significantly reduced due to strong exciton localization and Coulomb blockade effects, thus leading to limited photocurrent

Novel Air Flow Meter for an Automobile Engine Using a Si Sensor with Porous Si Thermal Isolation

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Model dielectric function analysis of the critical point features of silicon nanocrystal films in a broad parameter range

Due to quantum-confinement the band structure of silicon nanocrystals (NCs) is different from that of bulk silicon and strongly depends on the NC size. The samples we investigated have been prepared using chemical vapor deposition and annealing allowing a good control of the parameters in terms of both thickness and NC size, being suitable as model systems. The problem of the analysis is that the critical point features of the dielectric function can only be described with acceptable accuracy when using numerous parameters. The majority of the fit parameters are describing the oscillators of different line-shapes. In this work we show how the number of fit parameters can be reduced by a systematic analysis to find non-sensitive and correlating parameters to fix and couple as much parameters as possible

Rayonnement dans le substrat d'antennes intégrées sur silicium et silicium poreux

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