Compositional mapping of semiconductor quantum dots and rings

Biasiol, G.; Heun, S.

doi:10.1016/j.physrep.2010.12.001

Cited by 60 publications

(54 citation statements)

References 180 publications

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“…Therefrom, this simply suggests that the NMR spectra, especially in the Faraday geometry, can be utilized to extract the indium mole fraction, which is one of the key unknown material parameters for a specific QD under consideration. 38,39 D. NCSHFI-mediated nuclear spin depolarization Finally, we discuss within the Faraday configuration the NCSHFI-mediated nuclear spin depolarization, or for that matter the polarization process as well, as it is also governed by the same matrix element [cf. Eq.…”

Section: Nmr Spectramentioning

confidence: 99%

“…Considering different magnetic field orientations and the effect of random alloy mixing, i.e., In x Ga 1−x As QDs, critical insight is gained on the vulnerability of each nuclear spin transition in the NMR spectrum under inhomogeneous broadening. An important complication is that the mole fraction of the constituents can vary appreciably from dot to dot within the same sample, 38,39 rendering the in situ compositional identification of a targeted QD so far not practical. We demonstrate that this can be readily extracted from the main span of the NMR spectra.…”

Section: Introductionmentioning

confidence: 99%

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Quadrupolar spectra of nuclear spins in strained InxGa1−xAs quantum dots

Bulutay

2012

Phys. Rev. B

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Self-assembled quantum dots (QDs) are born out of lattice mismatched ingredients where strain plays an indispensable role. Through the electric quadrupolar coupling, strain affects the magnetic environment as seen by the nuclear spins. To guide prospective single-QD nuclear magnetic resonance (NMR), as well as dynamic nuclear spin polarization experiments, an atomistic insight to the strain and quadrupolar field distributions is presented. A number of implications of the structural and compositional profile of the QD have been identified. A high aspect ratio of the QD geometry enhances the quadrupolar interaction. The inclined interfaces introduce biaxiality and the tilting of the major quadrupolar principal axis away from the growth axis; the alloy mixing of gallium into the QD enhances both of these features while reducing the quadrupolar energy. Regarding the NMR spectra, both Faraday and Voigt geometries are investigated, unraveling in the first place the extend of inhomogeneous broadening and the appearance of the normally forbidden transitions. Moreover, it is shown that from the main extend of the NMR spectra the alloy mole fraction of a single QD can be inferred. By means of the element-resolved NMR intensities it is found that In nuclei has a factor of 5 dominance over those of As. In the presence of an external magnetic field, the borderlines between the quadrupolar and Zeeman regimes are extracted as 1.5 T for In and 1.1 T for As nuclei. At these values the nuclear spin depolarization rates of the respective nuclei get maximized due to the noncollinear secular hyperfine interaction with a resident electron in the QD.

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Section: Nmr Spectramentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quadrupolar spectra of nuclear spins in strained InxGa1−xAs quantum dots

Bulutay

2012

Phys. Rev. B

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“…We also inserted a lobe over the QD in the annealed sample. The Sb content was considered constant, and the QDs were not pure InAs [34,35]. The In content was assumed to change along the growth direction, with maximum In in the area with highest strain in the experimental deformation maps (i.e., 100% In for Sb28 and 80% In for Sb28-RTA) [34].…”

Section: Discussionmentioning

confidence: 99%

Effect of annealing in the Sb and In distribution of type II GaAsSb-capped InAs quantum dots

Reyes

Ulloa

Guzmán

et al. 2015

Semicond. Sci. Technol.

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Type II emission optoelectronic devices using GaAsSb strain reduction layers (SRL) over InAs quantum dots (QDs) have aroused great interest. Recent studies have demonstrated an extraordinary increase in photoluminescence (PL) intensity maintaining type II emission after a rapid thermal anneal (RTA), but with an undesirable blueshift. In this work, we have characterized the effect of RTA on InAs/GaAs QDs embedded in a SRL of GaAsSb by transmission electron microscopy (TEM) and finite element simulations. We find that annealing alters both the distribution of Sb in the SRL as well as the exchange of cations (In and Ga) between the QDs and the SRL. First, annealing causes modifications in the capping layer, reducing its thickness but maintaining the maximum Sb content and improving its homogeneity. In addition, the formation of Sb-rich clusters with loop dislocations is noticed, which seems not to be an impediment for an increased PL intensity. Second, RTA produces flatter QDs with larger base diameter and induces a more homogeneous QD height distribution. The Sb is accumulated over the QDs and the RTA enlarges the Sb-rich region, but the Sb contents are very similar. This fact leaves the type II alignment without major changes. Atomic-scale strain analysis of the nanostructures reveal a strong intermixing of In/Ga between the QDs and the capping layer, which is the main responsible mechanism of the PL blueshift. The improvement of the crystalline quality of the capping layer together with higher homogeneity QD sizes could be the origin of the enhancement of the PL emission.

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“…[1][2][3][4][5] During the past several years, the compositional state of these islands has been the subject of numerous investigations using many different techniques (see Ref. 6 as a review). The results provide evidence of significant intermixing with Si coming either from the substrate or from surface diffusion.…”

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confidence: 99%

Temperature evolution of defects and atomic ordering in Si1−xGex islands on Si(001)

Richard

Malachias

Stoffel

et al. 2016

Journal of Applied Physics

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Articles you may be interested in Persistent monolayer-scale chemical ordering in Si1−xGex heteroepitaxial films during surface roughening and strain relaxation J. Appl. Phys. 118, 245302 (2015); 10.1063/1.4938475Influence of composition and substrate miscut on the evolution of {105}-terminated in-plane Si1−xGex quantum wires on Si (001 The observation of atomic ordering and signatures of defects in self-assembled Ge islands using x-ray diffraction techniques have been previously treated as unrelated subjects. However, mutual understanding can be achieved when both subjects are studied in a common frame. Here, we report on measurements and analysis of both defects and atomic ordering in Si 1Àx Ge x islands epitaxially grown on Si(001) substrates as a function of growth temperature. By using x-ray diffraction and mapping around a bulk forbidden reflection, defect sizes, and in-plane spacing between nearby dislocations are extracted and related to the composition of the islands. The results fit well with an independent determination using selective wet chemical etching and atomic force microscopy measurements. Moreover, the temperature dependence of the ordered domain size is discussed. Although both atomic ordering and defect formation take place independently in the system, it is found that the relaxation provided by the onset of defects does not affect the formation of ordered domains, recently pointed out to be stabilized by strain and surface equilibrium on islands facets.

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Compositional mapping of semiconductor quantum dots and rings

Cited by 60 publications

References 180 publications

Quadrupolar spectra of nuclear spins in strained InxGa1−xAs quantum dots

Quadrupolar spectra of nuclear spins in strained InxGa1−xAs quantum dots

Effect of annealing in the Sb and In distribution of type II GaAsSb-capped InAs quantum dots

Temperature evolution of defects and atomic ordering in Si1−xGex islands on Si(001)

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