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Excitation Intensity Driven PL Shifts of SiGe Islands on Patterned and Planar Si(001) Substrates: Evidence for Ge-rich Dots in Islands.

Brehm M, Grydlik M, Hackl F, Lausecker E, Fromherz T, Bauer G - Nanoscale Res Lett (2010)

Bottom Line: For randomly nucleated SiGe/Si(001) islands, a significantly stronger blue-shift of the PL spectra as a function of the excitation intensity is observed when compared to islands grown on patterned substrates side by side within the same run in a solid source molecular beam epitaxy chamber.We ascribe this different PL behavior to the much larger inhomogeneity of the Ge distribution in islands on planar substrates when compared to islands grown on pit-patterned ones, as observed previously. 3D band-structure calculations show that Ge-rich inclusions of approximately 5 nm diameter at the apex of the islands can account for the observed differences in the PL spectra.The existence of such inclusions can be regarded as a quantum dot in an island and is in agreement with recent nano-tomography experiments.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Semiconductor and Solid State Physics, University of Linz, Altenbergerstrasse 69, 4040 Linz, Austria.

ABSTRACT
For randomly nucleated SiGe/Si(001) islands, a significantly stronger blue-shift of the PL spectra as a function of the excitation intensity is observed when compared to islands grown on patterned substrates side by side within the same run in a solid source molecular beam epitaxy chamber. We ascribe this different PL behavior to the much larger inhomogeneity of the Ge distribution in islands on planar substrates when compared to islands grown on pit-patterned ones, as observed previously. 3D band-structure calculations show that Ge-rich inclusions of approximately 5 nm diameter at the apex of the islands can account for the observed differences in the PL spectra. The existence of such inclusions can be regarded as a quantum dot in an island and is in agreement with recent nano-tomography experiments.

No MeSH data available.


a and b 3 × 3 μm AFM micrographs measured on uncapped samples (6 ML at TGe = 690°C) grown on a e-beam patterned Si(001) (pit-period = 400 nm) and b on planar Si(001). The color scale depicts the local surface slope with respect to (001). c PL spectra (Pexc = 2.6 W/cm2) of capped islands (6 ML at TGe = 700°C) grown on holographically patterned Si(001) (red) and planar Si(001) (black) substrates. A clear splitting of the NP peak and the TO replica is observed in the PL of ordered islands
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Figure 1: a and b 3 × 3 μm AFM micrographs measured on uncapped samples (6 ML at TGe = 690°C) grown on a e-beam patterned Si(001) (pit-period = 400 nm) and b on planar Si(001). The color scale depicts the local surface slope with respect to (001). c PL spectra (Pexc = 2.6 W/cm2) of capped islands (6 ML at TGe = 700°C) grown on holographically patterned Si(001) (red) and planar Si(001) (black) substrates. A clear splitting of the NP peak and the TO replica is observed in the PL of ordered islands

Mentions: Figures 1a, 1b show 3 × 3 μm2 AFM micrographs measured on uncapped islands, where 6 ML of Ge were deposited at TGe = 690°C on an e-beam pit-patterned Si(001) substrate with pit-period of 400 nm (Fig. 1a) and on a planar Si(001) substrate (Fig. 1b). The gray scale depicts the local surface slope with respect to the (001) surface. Darker color indicates steeper island facets. The islands in the pits are all multi-faceted domes [14] with dimensions of about 142 nm in base diameter and 24.5 nm in height. The islands grown on planar Si(001) substrates show the very well-known bimodal island distribution of pyramids and domes [2,5,15], where the domes have dimensions of about 117 nm in diameter and 20.1 nm in height. It is worth to mention that for the growth conditions used in this work, 94% of the islands grown on the planar substrate are dome shaped; therefore, it can be expected that these islands are contributing most to the island PL spectra discussed in the following. Figure 1c shows PL spectra (Pexc = 2.6 W/cm2) of islands (6 ML of Ge at TGe = 700°C) grown on a holographically patterned (red spectrum) and a planar Si(001) substrate (black spectrum). The PL spectrum measured on the planar Si(001) sample exhibits the well-known peaks stemming from the WL (the no-phonon transition (NP), transversal acoustical phonon-assisted transition and the transversal optical Si–Si phonon-assisted transition (TO) can be identified at 1.03, 1.013 and 0.975 eV, respectively) as well as the Si bulk phonon replica in the energy range from 1.025 to 1.15 eV. The PL signal originating from the islands at about 0.825 eV is relatively broad when compared to the island signal originating from the islands grown on the patterned substrate. Here, a clear splitting of the NP peak at 0.887 eV and the TO-phonon peak at 0.831 eV can be observed. As size quantization in these large islands is negligible, the narrowing of the emission lines can be attributed only to enhanced chemical uniformity of the islands grown on pit-patterned Si [7,9].


Excitation Intensity Driven PL Shifts of SiGe Islands on Patterned and Planar Si(001) Substrates: Evidence for Ge-rich Dots in Islands.

Brehm M, Grydlik M, Hackl F, Lausecker E, Fromherz T, Bauer G - Nanoscale Res Lett (2010)

a and b 3 × 3 μm AFM micrographs measured on uncapped samples (6 ML at TGe = 690°C) grown on a e-beam patterned Si(001) (pit-period = 400 nm) and b on planar Si(001). The color scale depicts the local surface slope with respect to (001). c PL spectra (Pexc = 2.6 W/cm2) of capped islands (6 ML at TGe = 700°C) grown on holographically patterned Si(001) (red) and planar Si(001) (black) substrates. A clear splitting of the NP peak and the TO replica is observed in the PL of ordered islands
© Copyright Policy
Related In: Results  -  Collection

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Figure 1: a and b 3 × 3 μm AFM micrographs measured on uncapped samples (6 ML at TGe = 690°C) grown on a e-beam patterned Si(001) (pit-period = 400 nm) and b on planar Si(001). The color scale depicts the local surface slope with respect to (001). c PL spectra (Pexc = 2.6 W/cm2) of capped islands (6 ML at TGe = 700°C) grown on holographically patterned Si(001) (red) and planar Si(001) (black) substrates. A clear splitting of the NP peak and the TO replica is observed in the PL of ordered islands
Mentions: Figures 1a, 1b show 3 × 3 μm2 AFM micrographs measured on uncapped islands, where 6 ML of Ge were deposited at TGe = 690°C on an e-beam pit-patterned Si(001) substrate with pit-period of 400 nm (Fig. 1a) and on a planar Si(001) substrate (Fig. 1b). The gray scale depicts the local surface slope with respect to the (001) surface. Darker color indicates steeper island facets. The islands in the pits are all multi-faceted domes [14] with dimensions of about 142 nm in base diameter and 24.5 nm in height. The islands grown on planar Si(001) substrates show the very well-known bimodal island distribution of pyramids and domes [2,5,15], where the domes have dimensions of about 117 nm in diameter and 20.1 nm in height. It is worth to mention that for the growth conditions used in this work, 94% of the islands grown on the planar substrate are dome shaped; therefore, it can be expected that these islands are contributing most to the island PL spectra discussed in the following. Figure 1c shows PL spectra (Pexc = 2.6 W/cm2) of islands (6 ML of Ge at TGe = 700°C) grown on a holographically patterned (red spectrum) and a planar Si(001) substrate (black spectrum). The PL spectrum measured on the planar Si(001) sample exhibits the well-known peaks stemming from the WL (the no-phonon transition (NP), transversal acoustical phonon-assisted transition and the transversal optical Si–Si phonon-assisted transition (TO) can be identified at 1.03, 1.013 and 0.975 eV, respectively) as well as the Si bulk phonon replica in the energy range from 1.025 to 1.15 eV. The PL signal originating from the islands at about 0.825 eV is relatively broad when compared to the island signal originating from the islands grown on the patterned substrate. Here, a clear splitting of the NP peak at 0.887 eV and the TO-phonon peak at 0.831 eV can be observed. As size quantization in these large islands is negligible, the narrowing of the emission lines can be attributed only to enhanced chemical uniformity of the islands grown on pit-patterned Si [7,9].

Bottom Line: For randomly nucleated SiGe/Si(001) islands, a significantly stronger blue-shift of the PL spectra as a function of the excitation intensity is observed when compared to islands grown on patterned substrates side by side within the same run in a solid source molecular beam epitaxy chamber.We ascribe this different PL behavior to the much larger inhomogeneity of the Ge distribution in islands on planar substrates when compared to islands grown on pit-patterned ones, as observed previously. 3D band-structure calculations show that Ge-rich inclusions of approximately 5 nm diameter at the apex of the islands can account for the observed differences in the PL spectra.The existence of such inclusions can be regarded as a quantum dot in an island and is in agreement with recent nano-tomography experiments.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Semiconductor and Solid State Physics, University of Linz, Altenbergerstrasse 69, 4040 Linz, Austria.

ABSTRACT
For randomly nucleated SiGe/Si(001) islands, a significantly stronger blue-shift of the PL spectra as a function of the excitation intensity is observed when compared to islands grown on patterned substrates side by side within the same run in a solid source molecular beam epitaxy chamber. We ascribe this different PL behavior to the much larger inhomogeneity of the Ge distribution in islands on planar substrates when compared to islands grown on pit-patterned ones, as observed previously. 3D band-structure calculations show that Ge-rich inclusions of approximately 5 nm diameter at the apex of the islands can account for the observed differences in the PL spectra. The existence of such inclusions can be regarded as a quantum dot in an island and is in agreement with recent nano-tomography experiments.

No MeSH data available.