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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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I-V characteristics obtained from films B and D at 200 K.
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Figure 2: I-V characteristics obtained from films B and D at 200 K.

Mentions: Figure 1 shows a schematic of a Si NC film and the experimental setup for the two terminal electrical measurements. Figures 2 and 3 show normalized I-V characteristics obtained from films B and D at 200 and 360 K respectively. The superlinear shape of the I-V characteristics, with a clear voltage threshold at low temperatures, was a result of the collective effect of the Si NCs involved in the transport which were separated by tunnel barriers and experienced Coulomb blockade effects due to their small sizes [3,25-29]. Indeed, it has been shown that the Coulomb blockade gap of an ordered array of identical islands and junctions exhibits a higher threshold voltage compared to a single island [30,31]. The increase of temperature caused a decrease of the threshold voltage, as carriers acquire enough energy to overcome the corresponding Coulomb blockade gaps. This was more evident in film D, which contained larger Si NCs. As a result, the I-V characteristics obtained from this film became linear at higher temperatures (see Figure 3). On the contrary, in films B and C, the I-V characteristics retained their superlinear shape even at higher temperatures. Film A was too resistive, showing an even larger threshold voltage at room temperature, whereas at lower temperatures it was impossible to measure any currents. This agrees well with the fact that the Si NCs within this film were too small and well separated with SiO2 potential barriers so that much larger biases were needed by the carriers to overcome the Coulomb gaps in the Si NCs.


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 obtained from films B and D at 200 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: I-V characteristics obtained from films B and D at 200 K.
Mentions: Figure 1 shows a schematic of a Si NC film and the experimental setup for the two terminal electrical measurements. Figures 2 and 3 show normalized I-V characteristics obtained from films B and D at 200 and 360 K respectively. The superlinear shape of the I-V characteristics, with a clear voltage threshold at low temperatures, was a result of the collective effect of the Si NCs involved in the transport which were separated by tunnel barriers and experienced Coulomb blockade effects due to their small sizes [3,25-29]. Indeed, it has been shown that the Coulomb blockade gap of an ordered array of identical islands and junctions exhibits a higher threshold voltage compared to a single island [30,31]. The increase of temperature caused a decrease of the threshold voltage, as carriers acquire enough energy to overcome the corresponding Coulomb blockade gaps. This was more evident in film D, which contained larger Si NCs. As a result, the I-V characteristics obtained from this film became linear at higher temperatures (see Figure 3). On the contrary, in films B and C, the I-V characteristics retained their superlinear shape even at higher temperatures. Film A was too resistive, showing an even larger threshold voltage at room temperature, whereas at lower temperatures it was impossible to measure any currents. This agrees well with the fact that the Si NCs within this film were too small and well separated with SiO2 potential barriers so that much larger biases were needed by the carriers to overcome the Coulomb gaps in the Si NCs.

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