Limits...
Optical characterization of In-flushed InAs/GaAs quantum dots emitting a broadband spectrum with multiple peaks at ~1 μm.

Kitamura S, Senshu M, Katsuyama T, Hino Y, Ozaki N, Ohkouchi S, Sugimoto Y, Hogg RA - Nanoscale Res Lett (2015)

Bottom Line: By using the In-flush technique for setting the height of self-assembled InAs QDs, we have tuned the emission wavelength of InAs QDs to the ~1 μm regime, which can be utilized as a non-invasive and deeply penetrative probe for biological and medical imaging systems.The controlled emission exhibited a broadband spectrum comprising multiple peaks with an interval of approximately 30 meV.This feature can be advantageous for realizing a broadband light source centered at the ~1 μm regime, which is especially suitable for the non-invasive cross-sectional biological and medical imaging system known as optical coherence tomography.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Engineering, University of Fukui, Fukui, 910-8507 Japan.

ABSTRACT
We investigated optical properties of In-flushed InAs quantum dots (QDs) grown on a GaAs substrate by molecular beam epitaxy. By using the In-flush technique for setting the height of self-assembled InAs QDs, we have tuned the emission wavelength of InAs QDs to the ~1 μm regime, which can be utilized as a non-invasive and deeply penetrative probe for biological and medical imaging systems. The controlled emission exhibited a broadband spectrum comprising multiple peaks with an interval of approximately 30 meV. We examined the origin of the multiple peaks using spectral and time-resolved photoluminescence, and concluded that it is attributed to monolayer step fluctuations in the height of the In-flushed QDs. This feature can be advantageous for realizing a broadband light source centered at the ~1 μm regime, which is especially suitable for the non-invasive cross-sectional biological and medical imaging system known as optical coherence tomography.

No MeSH data available.


Related in: MedlinePlus

a LNT PL spectrum obtained from the In-flushed QDs. b PL time decay measured at peaks B and C shown in a
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4446289&req=5

Fig4: a LNT PL spectrum obtained from the In-flushed QDs. b PL time decay measured at peaks B and C shown in a

Mentions: As seen in the RT–PL (Fig. 3b), normalized emission peaks A–C (1.11, 1.14, and 1.17 eV) exhibit identical intensities as a function of the excitation power, whereas the emission intensity spanning 1.18–1.26 eV increases slightly. This suggests that emission peaks A–C originate from the GS emissions of the In-flushed QDs with different heights, and the emissions at 1.18–1.26 eV include the ES emissions of the QDs in addition to the GS emissions of QDs at 1.20 eV (peak D). The difference in the emission line compared to the fitting line can be attributed to the additional ES emissions. In order to confirm this scenario, we measured the time-resolved PL for the In-flushed QD sample and verified the origins of the emissions. Figure 4a shows a PL spectrum obtained from the In-flushed QDs at LNT. This spectrum can also be fitted with multiple Gaussian peaks A–C (1.22, 1.25, and 1.28 eV) and broad emissions spanning 1.30–1.35 and 1.35–1.42 eV. These can originate from the corresponding emission centers seen in the RT–PL spectrum, whose energy values shift with the temperature decrease. In the broad emission spanning 1.30–1.35 eV, the ES emissions and the GS emission that peaks at approximately 1.32 eV (peak D) are included. The difference between the emission line and the fitting line (dashed gray line) could be due to the additional ES emissions. The emission spanning 1.35–1.42 eV, which is centered at approximately 1.39 eV, should be from InAs WL. We first measure the PL time evolution of apparent peaks B and C. As shown in Fig. 4b, the photoluminescence intensity initially rises and exhibits a peak at approximately 300 ps after the excitation and then falls with a single exponential decay. The time scale is indicated with the intensity peak time as zero. The rise time can be understood as the time for the creation of photoexcited carriers in the GaAs layer and the capture of these carriers by QDs through InAs WL. In addition, in the short-time range (~0.6 ns), there is a slight fluctuation in the PL decay, which is especially obvious in peak B. This could be influenced by the relaxation process from the InAs WL to the GS state through the ES states of the QD, as discussed in the next paragraph. However, the main decays of peaks B and C can be fitted with a single exponential curve, and the decay times are estimated to be 0.85 and 0.81 ns, respectively. When considering that the typical decay time of the emission from the GS of InAs/GaAs QDs is ~1 ns [23–26], these results demonstrate that the peaks originate from the GS of QDs with a different height of one ML, as was previously discussed regarding the RT–PL result.Fig. 4


Optical characterization of In-flushed InAs/GaAs quantum dots emitting a broadband spectrum with multiple peaks at ~1 μm.

Kitamura S, Senshu M, Katsuyama T, Hino Y, Ozaki N, Ohkouchi S, Sugimoto Y, Hogg RA - Nanoscale Res Lett (2015)

a LNT PL spectrum obtained from the In-flushed QDs. b PL time decay measured at peaks B and C shown in a
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4446289&req=5

Fig4: a LNT PL spectrum obtained from the In-flushed QDs. b PL time decay measured at peaks B and C shown in a
Mentions: As seen in the RT–PL (Fig. 3b), normalized emission peaks A–C (1.11, 1.14, and 1.17 eV) exhibit identical intensities as a function of the excitation power, whereas the emission intensity spanning 1.18–1.26 eV increases slightly. This suggests that emission peaks A–C originate from the GS emissions of the In-flushed QDs with different heights, and the emissions at 1.18–1.26 eV include the ES emissions of the QDs in addition to the GS emissions of QDs at 1.20 eV (peak D). The difference in the emission line compared to the fitting line can be attributed to the additional ES emissions. In order to confirm this scenario, we measured the time-resolved PL for the In-flushed QD sample and verified the origins of the emissions. Figure 4a shows a PL spectrum obtained from the In-flushed QDs at LNT. This spectrum can also be fitted with multiple Gaussian peaks A–C (1.22, 1.25, and 1.28 eV) and broad emissions spanning 1.30–1.35 and 1.35–1.42 eV. These can originate from the corresponding emission centers seen in the RT–PL spectrum, whose energy values shift with the temperature decrease. In the broad emission spanning 1.30–1.35 eV, the ES emissions and the GS emission that peaks at approximately 1.32 eV (peak D) are included. The difference between the emission line and the fitting line (dashed gray line) could be due to the additional ES emissions. The emission spanning 1.35–1.42 eV, which is centered at approximately 1.39 eV, should be from InAs WL. We first measure the PL time evolution of apparent peaks B and C. As shown in Fig. 4b, the photoluminescence intensity initially rises and exhibits a peak at approximately 300 ps after the excitation and then falls with a single exponential decay. The time scale is indicated with the intensity peak time as zero. The rise time can be understood as the time for the creation of photoexcited carriers in the GaAs layer and the capture of these carriers by QDs through InAs WL. In addition, in the short-time range (~0.6 ns), there is a slight fluctuation in the PL decay, which is especially obvious in peak B. This could be influenced by the relaxation process from the InAs WL to the GS state through the ES states of the QD, as discussed in the next paragraph. However, the main decays of peaks B and C can be fitted with a single exponential curve, and the decay times are estimated to be 0.85 and 0.81 ns, respectively. When considering that the typical decay time of the emission from the GS of InAs/GaAs QDs is ~1 ns [23–26], these results demonstrate that the peaks originate from the GS of QDs with a different height of one ML, as was previously discussed regarding the RT–PL result.Fig. 4

Bottom Line: By using the In-flush technique for setting the height of self-assembled InAs QDs, we have tuned the emission wavelength of InAs QDs to the ~1 μm regime, which can be utilized as a non-invasive and deeply penetrative probe for biological and medical imaging systems.The controlled emission exhibited a broadband spectrum comprising multiple peaks with an interval of approximately 30 meV.This feature can be advantageous for realizing a broadband light source centered at the ~1 μm regime, which is especially suitable for the non-invasive cross-sectional biological and medical imaging system known as optical coherence tomography.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Engineering, University of Fukui, Fukui, 910-8507 Japan.

ABSTRACT
We investigated optical properties of In-flushed InAs quantum dots (QDs) grown on a GaAs substrate by molecular beam epitaxy. By using the In-flush technique for setting the height of self-assembled InAs QDs, we have tuned the emission wavelength of InAs QDs to the ~1 μm regime, which can be utilized as a non-invasive and deeply penetrative probe for biological and medical imaging systems. The controlled emission exhibited a broadband spectrum comprising multiple peaks with an interval of approximately 30 meV. We examined the origin of the multiple peaks using spectral and time-resolved photoluminescence, and concluded that it is attributed to monolayer step fluctuations in the height of the In-flushed QDs. This feature can be advantageous for realizing a broadband light source centered at the ~1 μm regime, which is especially suitable for the non-invasive cross-sectional biological and medical imaging system known as optical coherence tomography.

No MeSH data available.


Related in: MedlinePlus