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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.


PL spectra obtained at different Pexc for islands on a planar Si(001) substrate. The island PL shifts strongly with increasing excitation power from 0.77 eV at Pexc = 16 mW/cm2 to 0.86 eV at Pexc = 244.3 W/cm2. The detector cut-off at 0.77 eV is indicated by the dashed line. The spectra are shifted vertically for clarity
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Figure 3: PL spectra obtained at different Pexc for islands on a planar Si(001) substrate. The island PL shifts strongly with increasing excitation power from 0.77 eV at Pexc = 16 mW/cm2 to 0.86 eV at Pexc = 244.3 W/cm2. The detector cut-off at 0.77 eV is indicated by the dashed line. The spectra are shifted vertically for clarity

Mentions: Figure 3 shows PL spectra measured on the islands grown on planar Si(001) as a function of Pexc. The same behavior as described for the ordered islands shown in Fig. 2 is observed for the Si bulk phonon replica. The WL signal is stronger in intensity when compared to the one measured for islands grown on the pit-patterned substrate, which can be explained by the higher area of uniform WL thickness on planar Si(001). The WL peak positions of the NP transition and the TO-phonon transition are observed at 1.03 and 0.973 eV, respectively, for Pexc = 16 mW/cm2 and exhibit only a minor blue-shift (to 0.979 and 1.035 eV) by increasing Pexc to 244 W/cm2. By comparing Figs. 2 and 3, it is obvious that there exists a dramatic difference between the Pexc dependencies of the PL emission of the islands grown on pit-patterned substrate (Fig. 2) and the one of islands grown on planar Si (Fig. 3). While for the ordered islands, the PL emission does not shift significantly with Pexc, it does shift by more than 90 meV when increasing Pexc from 33 mW/cm2 to 244.3 W/cm2 in the case of the islands on the planar substrate. Due to the cut-off energy of the InGaAs detector, the energetic position of the PL peak emission for Pexc < 33 mW/cm2 cannot be determined exactly. Similar findings have been reported for smaller pit periods and lower growth temperatures in [17] and were ascribed to the large size inhomogeneity and a concomitant inter-dot Ge concentration inhomogeneity. However, in our samples, we observe within the domes on the planar sample (94% of all islands, height: 20.1 ± 0.1 nm) a similar size distribution as for the domes on the patterned samples. Thus, this model cannot be applied to the islands in our experiments.


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)

PL spectra obtained at different Pexc for islands on a planar Si(001) substrate. The island PL shifts strongly with increasing excitation power from 0.77 eV at Pexc = 16 mW/cm2 to 0.86 eV at Pexc = 244.3 W/cm2. The detector cut-off at 0.77 eV is indicated by the dashed line. The spectra are shifted vertically for clarity
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Related In: Results  -  Collection

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Figure 3: PL spectra obtained at different Pexc for islands on a planar Si(001) substrate. The island PL shifts strongly with increasing excitation power from 0.77 eV at Pexc = 16 mW/cm2 to 0.86 eV at Pexc = 244.3 W/cm2. The detector cut-off at 0.77 eV is indicated by the dashed line. The spectra are shifted vertically for clarity
Mentions: Figure 3 shows PL spectra measured on the islands grown on planar Si(001) as a function of Pexc. The same behavior as described for the ordered islands shown in Fig. 2 is observed for the Si bulk phonon replica. The WL signal is stronger in intensity when compared to the one measured for islands grown on the pit-patterned substrate, which can be explained by the higher area of uniform WL thickness on planar Si(001). The WL peak positions of the NP transition and the TO-phonon transition are observed at 1.03 and 0.973 eV, respectively, for Pexc = 16 mW/cm2 and exhibit only a minor blue-shift (to 0.979 and 1.035 eV) by increasing Pexc to 244 W/cm2. By comparing Figs. 2 and 3, it is obvious that there exists a dramatic difference between the Pexc dependencies of the PL emission of the islands grown on pit-patterned substrate (Fig. 2) and the one of islands grown on planar Si (Fig. 3). While for the ordered islands, the PL emission does not shift significantly with Pexc, it does shift by more than 90 meV when increasing Pexc from 33 mW/cm2 to 244.3 W/cm2 in the case of the islands on the planar substrate. Due to the cut-off energy of the InGaAs detector, the energetic position of the PL peak emission for Pexc < 33 mW/cm2 cannot be determined exactly. Similar findings have been reported for smaller pit periods and lower growth temperatures in [17] and were ascribed to the large size inhomogeneity and a concomitant inter-dot Ge concentration inhomogeneity. However, in our samples, we observe within the domes on the planar sample (94% of all islands, height: 20.1 ± 0.1 nm) a similar size distribution as for the domes on the patterned samples. Thus, this model cannot be applied to the islands in our experiments.

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.