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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.


ER spectra for QD sample under various bias voltages shifted vertically for clarity.
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Figure 4: ER spectra for QD sample under various bias voltages shifted vertically for clarity.

Mentions: Figure 3a shows typical results of ER spectroscopy. We did not observe any ER signal in a reference sample and in a sample with Ge WLs. Instead, there is an apparent, well-defined ER response from a sample containing Ge QDs. We thus associate this electromodulation with Ge nanoislands. In order to accurately determine the transition energies, we fit the data with a first-derivative Gaussian-type function [8]. The Gaussian line-shape analysis is appropriate for the inhomogeneous broadening related to the size fluctuations in ensemble of QDs. A typical curve fit is demonstrated in Figure 3b for the reverse bias of 1.5 V. As shown by the full line, a satisfactory fitting is achieved when one assumes the presence of three transitions (A, B, and C) with the energies denoted by thin vertical lines. Note that the position of the low-energy feature is close to the long-wave PC onset. Figure 4 shows the ER as a function of reverse bias applied to the diode. The low-energy reflectance modulation at 400 meV disappears at large applied voltage when the residual holes are evacuated from the dots and the Ge islands become completely depleted. We assume that this resonance corresponds to the hole intraband transition between the ground state in Ge QDs and the valence band continuum. This assignment is further supported by theoretical consideration presented below.


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

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

ER spectra for QD sample under various bias voltages shifted vertically for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: ER spectra for QD sample under various bias voltages shifted vertically for clarity.
Mentions: Figure 3a shows typical results of ER spectroscopy. We did not observe any ER signal in a reference sample and in a sample with Ge WLs. Instead, there is an apparent, well-defined ER response from a sample containing Ge QDs. We thus associate this electromodulation with Ge nanoislands. In order to accurately determine the transition energies, we fit the data with a first-derivative Gaussian-type function [8]. The Gaussian line-shape analysis is appropriate for the inhomogeneous broadening related to the size fluctuations in ensemble of QDs. A typical curve fit is demonstrated in Figure 3b for the reverse bias of 1.5 V. As shown by the full line, a satisfactory fitting is achieved when one assumes the presence of three transitions (A, B, and C) with the energies denoted by thin vertical lines. Note that the position of the low-energy feature is close to the long-wave PC onset. Figure 4 shows the ER as a function of reverse bias applied to the diode. The low-energy reflectance modulation at 400 meV disappears at large applied voltage when the residual holes are evacuated from the dots and the Ge islands become completely depleted. We assume that this resonance corresponds to the hole intraband transition between the ground state in Ge QDs and the valence band continuum. This assignment is further supported by theoretical consideration presented below.

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.