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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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Photocurrent normalized to the power of incident light and absorption spectrum for film C.
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Figure 6: Photocurrent normalized to the power of incident light and absorption spectrum for film C.

Mentions: In photocurrent measurements a DC electric field was applied between two electrodes in order to separate the photo-generated electron hole pairs and collect the electrons and holes which were generated within the Si NCs in the films by illumination with light of energy above the bandgap of the material. In Figure 6, a comparison is shown between photocurrent normalized to the power of the incident light and absorption spectra obtained from film C. The two spectra fit perfectly one upon the other, confirming that the observed photocurrent is indeed due to carriers generated in the Si NCs within the films when the energy of the illumination becomes higher that the energy bandgap of the Si NCs. The peak at 1.95 eV which is only present in the photocurrent spectra of all films is associated with a defect in the silica matrix, the so-called non-bridging oxygen hole center, which has an absorption band at this energy [38,39]. These centers can trap electrons in the silica matrix, which can be released and contribute to the photocurrent once the energy of the illumination reaches 1.95 eV.


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)

Photocurrent normalized to the power of incident light and absorption spectrum for film C.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Photocurrent normalized to the power of incident light and absorption spectrum for film C.
Mentions: In photocurrent measurements a DC electric field was applied between two electrodes in order to separate the photo-generated electron hole pairs and collect the electrons and holes which were generated within the Si NCs in the films by illumination with light of energy above the bandgap of the material. In Figure 6, a comparison is shown between photocurrent normalized to the power of the incident light and absorption spectra obtained from film C. The two spectra fit perfectly one upon the other, confirming that the observed photocurrent is indeed due to carriers generated in the Si NCs within the films when the energy of the illumination becomes higher that the energy bandgap of the Si NCs. The peak at 1.95 eV which is only present in the photocurrent spectra of all films is associated with a defect in the silica matrix, the so-called non-bridging oxygen hole center, which has an absorption band at this energy [38,39]. These centers can trap electrons in the silica matrix, which can be released and contribute to the photocurrent once the energy of the illumination reaches 1.95 eV.

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