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

as a function of energy of the incident light.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: as a function of energy of the incident light.

Mentions: Absorption measurements were obtained from all films at room temperature, as shown in Figure 5. The figure shows plots of the square root of a(λ) in Equation 1, as a function of the energy of the incident light on the film, for the different films. The linear dependence of on the energy of illumination shows that the Si NCs within the films have indirect bandgaps. By extrapolating the linear part of the plots to = 0, one can estimate the average bandgap Eg of the Si NCs within the films. A clear bandgap upshift can be observed with decreasing nanocrystal size. For film D, Eg was 1.19 eV; for film C, Eg was 1.27 eV; for film B, Eg was 1.32 eV. In film A, containing Si NCs with sizes less than 2 nm, we observed two linear parts in the plot as a function of energy. These correspond to two different onsets in the absorption. The first one occurs at 1.75 eV, while the second one at 2.5 eV (found by extrapolating the second linear part of the plot to = 0, in Figure 5). Higher absorption than in bulk Si in the visible and ultraviolet regions is observed.


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)

as a function of energy of the incident light.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: as a function of energy of the incident light.
Mentions: Absorption measurements were obtained from all films at room temperature, as shown in Figure 5. The figure shows plots of the square root of a(λ) in Equation 1, as a function of the energy of the incident light on the film, for the different films. The linear dependence of on the energy of illumination shows that the Si NCs within the films have indirect bandgaps. By extrapolating the linear part of the plots to = 0, one can estimate the average bandgap Eg of the Si NCs within the films. A clear bandgap upshift can be observed with decreasing nanocrystal size. For film D, Eg was 1.19 eV; for film C, Eg was 1.27 eV; for film B, Eg was 1.32 eV. In film A, containing Si NCs with sizes less than 2 nm, we observed two linear parts in the plot as a function of energy. These correspond to two different onsets in the absorption. The first one occurs at 1.75 eV, while the second one at 2.5 eV (found by extrapolating the second linear part of the plot to = 0, in Figure 5). Higher absorption than in bulk Si in the visible and ultraviolet regions is observed.

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