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Electromodulated reflectance study of self-assembled Ge/Si quantum dots.

Yakimov A, Nikiforov A, Bloshkin A, Dvurechenskii A - Nanoscale Res Lett (2011)

Bottom Line: Up to three optical transitions are observed.The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band.The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia. yakimov@isp.nsc.ru.

ABSTRACT
We perform an electroreflectance spectroscopy of Ge/Si self-assembled quantum dots in the near-infrared and in the mid-infrared spectral range. Up to three optical transitions are observed. The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band. The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.

No MeSH data available.


Related in: MedlinePlus

Schematic cross section of the QD device used to make photocur-rent and ER measurements. The structure is that of a p-i-n diode with 20 layers of Ge QDs in the depleted intrinsic region.
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Figure 1: Schematic cross section of the QD device used to make photocur-rent and ER measurements. The structure is that of a p-i-n diode with 20 layers of Ge QDs in the depleted intrinsic region.

Mentions: For controlled tuning of the electric field, the Ge QDs are embedded in the intrinsic region of a Si pin diode, allowing fields to be applied parallel the growth direction. To rule out spurious effects and to correctly assign the spectral features due to the presence of the dots, three sets of samples were grown by means of molecular beam epitaxy (MBE) on a p-Si(001) substrate with a resistivity of 150 Ω cm. The first one contains no Ge and hence can be considered as a reference sample. The second sample contains twenty Ge wetting layers (WLs), each 4 monolayer (ML) thick. A WL represents thin Ge planar layer which forms during the early stage of Ge deposition. And finally, there is a sample with 20 layers of Ge QDs lying on WLs (Figure 1). The growth temperature was generally 500°C for all layers. First, a 500-nm Sb-doped n+-type Si buffer layer with doping concentration of 5 × 1018 cm-3 followed by a 200-nm Si undoped layer were grown. Then 20 Ge layers separated by 10-nm Si spacer layer, followed by a 100-nm undoped Si layer, were fabricated at a rate of 0.02 ML/s. For all samples the Ge coverage is about 6 ML. The Ge QDs formation was controlled by reflection high energy electron diffraction when the pattern changed from streaky to spotty. Immediately after the deposition of Ge, the temperature was lowered to Ts = 350-400°C and the Ge islands are covered by a 1-nm Si layer. This procedure is necessary to minimize Ge-Si intermixing and to preserve island shape and size from the effect of a further higher temperature deposition. The average Ge content of 80% in the nanoclusters was determined from Raman measurements. The samples were completed by capping a 300-nm-thick p+-doped Si layer (B, 3 × 1018 cm-3) to form a p-i-n junction. The resulting devices were isolated from each other by etching 1.1-μm-deep mesas.


Electromodulated reflectance study of self-assembled Ge/Si quantum dots.

Yakimov A, Nikiforov A, Bloshkin A, Dvurechenskii A - Nanoscale Res Lett (2011)

Schematic cross section of the QD device used to make photocur-rent and ER measurements. The structure is that of a p-i-n diode with 20 layers of Ge QDs in the depleted intrinsic region.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211264&req=5

Figure 1: Schematic cross section of the QD device used to make photocur-rent and ER measurements. The structure is that of a p-i-n diode with 20 layers of Ge QDs in the depleted intrinsic region.
Mentions: For controlled tuning of the electric field, the Ge QDs are embedded in the intrinsic region of a Si pin diode, allowing fields to be applied parallel the growth direction. To rule out spurious effects and to correctly assign the spectral features due to the presence of the dots, three sets of samples were grown by means of molecular beam epitaxy (MBE) on a p-Si(001) substrate with a resistivity of 150 Ω cm. The first one contains no Ge and hence can be considered as a reference sample. The second sample contains twenty Ge wetting layers (WLs), each 4 monolayer (ML) thick. A WL represents thin Ge planar layer which forms during the early stage of Ge deposition. And finally, there is a sample with 20 layers of Ge QDs lying on WLs (Figure 1). The growth temperature was generally 500°C for all layers. First, a 500-nm Sb-doped n+-type Si buffer layer with doping concentration of 5 × 1018 cm-3 followed by a 200-nm Si undoped layer were grown. Then 20 Ge layers separated by 10-nm Si spacer layer, followed by a 100-nm undoped Si layer, were fabricated at a rate of 0.02 ML/s. For all samples the Ge coverage is about 6 ML. The Ge QDs formation was controlled by reflection high energy electron diffraction when the pattern changed from streaky to spotty. Immediately after the deposition of Ge, the temperature was lowered to Ts = 350-400°C and the Ge islands are covered by a 1-nm Si layer. This procedure is necessary to minimize Ge-Si intermixing and to preserve island shape and size from the effect of a further higher temperature deposition. The average Ge content of 80% in the nanoclusters was determined from Raman measurements. The samples were completed by capping a 300-nm-thick p+-doped Si layer (B, 3 × 1018 cm-3) to form a p-i-n junction. The resulting devices were isolated from each other by etching 1.1-μm-deep mesas.

Bottom Line: Up to three optical transitions are observed.The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band.The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia. yakimov@isp.nsc.ru.

ABSTRACT
We perform an electroreflectance spectroscopy of Ge/Si self-assembled quantum dots in the near-infrared and in the mid-infrared spectral range. Up to three optical transitions are observed. The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band. The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and Δ(4) valleys of the Ge conduction band, and the localized hole states at the Γ point.

No MeSH data available.


Related in: MedlinePlus