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

Gardelis S, Manousiadis P, Nassiopoulou AG - Nanoscale Res Lett (2011)

Bottom Line: Electronic transport is determined by the collective effect of Coulomb blockade gaps in the Si NCs.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: IMEL/NCSR Demokritos, Terma Patriarchou Grigoriou, Aghia Paraskevi, 15310 Athens, Greece. S.Gardelis@imel.demokritos.gr.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

I-V characteristics for film B, in dark and under illumination.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211285&req=5

Figure 7: I-V characteristics for film B, in dark and under illumination.

Mentions: I-V characteristics were obtained under illumination at different wavelengths at room temperature. Generally, we observed an increase of current with increasing intensity of illumination for energies above the bandgap of Si NCs within the films B, C, and D. This is expected, as photons of these energies generate electron hole pairs within the Si NCs. We also examined the role of the illumination wavelength on the photocurrent. In Figure 7, a comparison between normalized room temperature I-V characteristics obtained from film B respectively in the dark, under illumination at 700 nm (or 1.77 eV), and under illumination at 300 nm (or 3.44 eV), is shown. It is evident that the shape of the normalized I-V curves changes significantly in the case of illumination at 360 nm. The shape of the I-V curve changes from superlinear in the dark to linear under illumination at 360 nm. However, illumination at 700 nm causes a smaller change in the shape of the I-V curve. According to the above analysis of the electrical measurements, the shape of the I-V curve in the dark is determined by the Coulomb gap of the Si NCs within the film. Thus, at higher energies of illumination, carriers acquire sufficient energy to overcome the Coulomb gaps within the Si NCs, resulting in a linear I-V characteristic.


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

Gardelis S, Manousiadis P, Nassiopoulou AG - Nanoscale Res Lett (2011)

I-V characteristics for film B, in dark and under illumination.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211285&req=5

Figure 7: I-V characteristics for film B, in dark and under illumination.
Mentions: I-V characteristics were obtained under illumination at different wavelengths at room temperature. Generally, we observed an increase of current with increasing intensity of illumination for energies above the bandgap of Si NCs within the films B, C, and D. This is expected, as photons of these energies generate electron hole pairs within the Si NCs. We also examined the role of the illumination wavelength on the photocurrent. In Figure 7, a comparison between normalized room temperature I-V characteristics obtained from film B respectively in the dark, under illumination at 700 nm (or 1.77 eV), and under illumination at 300 nm (or 3.44 eV), is shown. It is evident that the shape of the normalized I-V curves changes significantly in the case of illumination at 360 nm. The shape of the I-V curve changes from superlinear in the dark to linear under illumination at 360 nm. However, illumination at 700 nm causes a smaller change in the shape of the I-V curve. According to the above analysis of the electrical measurements, the shape of the I-V curve in the dark is determined by the Coulomb gap of the Si NCs within the film. Thus, at higher energies of illumination, carriers acquire sufficient energy to overcome the Coulomb gaps within the Si NCs, resulting in a linear I-V characteristic.

Bottom Line: Electronic transport is determined by the collective effect of Coulomb blockade gaps in the Si NCs.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: IMEL/NCSR Demokritos, Terma Patriarchou Grigoriou, Aghia Paraskevi, 15310 Athens, Greece. S.Gardelis@imel.demokritos.gr.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus