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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.


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PL and absorption spectra obtained from film A at room temperature.
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Figure 8: PL and absorption spectra obtained from film A at room temperature.

Mentions: PL measurements were performed in all films at room temperature. Only the film A which contains Si NCs of sizes less than 2 nm, showed light emission. An example of PL spectrum is shown in Figure 8. Efficient light emission at room temperature from this film is attributed to the small size of the NCs (strong confinement) and their separation by SiO2 barriers. Their discrete character explains also the fact that no photocurrent was observed in this sample. By comparing the PL and absorption spectra (shown in Figure 8) we notice the following: Two different energy onsets are observed in absorption. The first occurred at 1.75 eV, whereas the second, which is sharper, occurred at 2.5 eV. The first absorption onset is within the spectral range of the PL spectrum (1.4 eV-2 eV) and is attributed to transitions involving Si NC/SiO2 interface states [17-24]. The second sharper absorption onset at 2.5 eV can be attributed to the energy bandgap, Eg, of the Si NCs within the film. According to theoretical calculations such an energy gap corresponds to Si NCs with sizes of less than 2 nm [20,40]. This agrees well with the sizes of the Si NCs within this film.


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)

PL and absorption spectra obtained from film A at room temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: PL and absorption spectra obtained from film A at room temperature.
Mentions: PL measurements were performed in all films at room temperature. Only the film A which contains Si NCs of sizes less than 2 nm, showed light emission. An example of PL spectrum is shown in Figure 8. Efficient light emission at room temperature from this film is attributed to the small size of the NCs (strong confinement) and their separation by SiO2 barriers. Their discrete character explains also the fact that no photocurrent was observed in this sample. By comparing the PL and absorption spectra (shown in Figure 8) we notice the following: Two different energy onsets are observed in absorption. The first occurred at 1.75 eV, whereas the second, which is sharper, occurred at 2.5 eV. The first absorption onset is within the spectral range of the PL spectrum (1.4 eV-2 eV) and is attributed to transitions involving Si NC/SiO2 interface states [17-24]. The second sharper absorption onset at 2.5 eV can be attributed to the energy bandgap, Eg, of the Si NCs within the film. According to theoretical calculations such an energy gap corresponds to Si NCs with sizes of less than 2 nm [20,40]. This agrees well with the sizes of the Si NCs within this film.

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