Non-substitutional Sn Defects in Ge1−x Sn x Alloys for Opto- and Nanoelectronics

Barrio, Rafael A.; Querales-Flores, José D.; Fuhr, J. D.; Ventura, C. I.

doi:10.1007/s10948-011-1401-4

Cited by 4 publications

(14 citation statements)

References 8 publications

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“…For instance, these defects could (i) reduce the carrier mobility in the Ge 1Àx Sn x layers and increase their contact resistance, (ii) compromise their effectiveness as stressors, or (iii) increase the minimum Sn concentration required to obtain direct bandgap materials. 9 These EXAFS results can be useful to develop more accurate VCA-based or atomistic models of Ge 1Àx Sn x by including an experimentally verified description of the local surrounding of the Sn atoms. Within the accuracy of these measurements, the different SRDs of the examined layers are not reflected in the local atomic surrounding of the Sn atoms.…”

Section: Discussionmentioning

confidence: 98%

“…In fact, the presence of SV complexes would have increased the minimum Sn concentration necessary to achieve a direct bandgap material. 9 Ventura et al 3 determined a temperaturedependent critical Sn concentration (20 at. % Sn at room temperature) beyond which the formation of these complexes is favorable in thermal equilibrium.…”

Section: A Sn Incorporation's Configuration In the Ge Latticementioning

confidence: 99%

“…The Sn incorporation configuration influences the Ge 1Àx Sn x crystallographic, electrical, and optical properties. 8,10 For example, theoretical investigations 9 show that the presence of SV complexes increases the minimum Sn concentration needed to have direct bandgap Ge 1Àx Sn x . Therefore, recognizing and controlling the presence of specific Sn-vacancy complexes, Sn clusters (i.e., aggregations of two or more Sn atoms directly bonding), or Sn interstitials is also important from an application point of view.…”

mentioning

confidence: 99%

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Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

Gencarelli

Grandjean

Shimura

et al. 2015

Journal of Applied Physics

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We present an extended X-ray absorption fine structure investigation of the local environment of Sn atoms in strained and relaxed Ge1−xSnx layers with different compositions. We show that the preferred configuration for the incorporation of Sn atoms in these Ge1−xSnx layers is that of a α-Sn defect, with each Sn atom covalently bonded to four Ge atoms in a classic tetrahedral configuration. Sn interstitials, Sn-split vacancy complexes, or Sn dimers, if present at all, are not expected to involve more than 2.5% of the total Sn atoms. This finding, along with a relative increase of Sn atoms in the second atomic shell around a central Sn atom in Ge1−xSnx layers with increasing Sn concentrations, suggests that the investigated materials are homogeneous random substitutional alloys. Within the accuracy of the measurements, the degree of strain relaxation of the Ge1−xSnx layers does not have a significant impact on the local atomic surrounding of the Sn atoms. Finally, the calculated topological rigidity parameter a** = 0.69 ± 0.29 indicates that the strain due to alloying in Ge1−xSnx is accommodated via bond stretching and bond bending, with a slight predominance of the latter, in agreement with ab initio calculations reported in literature.

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Section: Discussionmentioning

confidence: 98%

Section: A Sn Incorporation's Configuration In the Ge Latticementioning

confidence: 99%

mentioning

confidence: 99%

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Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

Gencarelli

Grandjean

Shimura

et al. 2015

Journal of Applied Physics

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“…A. Effective substitutional two-site cluster equivalent to the non-substitutional β-Sn defect As mentioned above, in a previous work 35 we determined and compared two effective substitutional twosite clusters equivalent to the real non-substitutional β-Sn defects: schematically represented in Fig.1. In Fig.1.…”

Section: Inclusion Of β-Sn Non-substitutional Complex Defects In mentioning

confidence: 99%

“…(b) represents an equivalent cluster composed by two substitutional sites, where the effective atoms occupying each site in the cluster have an energy denoted by E γ 1 (considered to be equal in both sites of the cluster, by symmetry). 35 The equivalence was established under the following conditions: (1) for simplicity, we propose that the equivalence is valid for each separate orbital; (2) we assume that only interactions between orbitals of the same type between nearest-neighbour (NN) atoms are relevant; and (3) we demand that the local Green's functions in the original and equivalent problems are equal, and will thus have the same analytical properties.…”

Section: Inclusion Of β-Sn Non-substitutional Complex Defects In mentioning

confidence: 99%

The two gap transitions in Ge1−xSnx: Effect of non-substitutional complex defects

Querales-Flores

Ventura

Fuhr

et al. 2016

Journal of Applied Physics

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The existence of non-substitutional β-Sn defects in Ge 1−x Sn x was confirmed by emission channeling experiments [Decoster et al., Phys. Rev. B 81, 155204 (2010)], which established that although most Sn enters substitutionally (α-Sn) in the Ge lattice, a second significant fraction corresponds to the Sn-vacancy defect complex in the split-vacancy configuration ( β-Sn ), in agreement with our previous theoretical study [Ventura et al., Phys. Rev. B 79, 155202 (2009)]. Here, we present our electronic structure calculation for Ge 1−x Sn x , including substitutional α-Sn as well as non-substitutional β-Sn defects. To include the presence of non-substitutional complex defects in the electronic structure calculation for this multi-orbital alloy problem, we extended the approach for the purely substitutional alloy by Jenkins and Dow [Jenkins and Dow, Phys. Rev. B 36, 7994 (1987)]. We employed an effective substitutional two-site cluster equivalent to the real non-substitutional β-Sn defect, which was determined by a Green's functions calculation. We then calculated the electronic structure of the effective alloy purely in terms of substitutional defects, embedding the effective substitutional clusters in the lattice. Our results describe the two transitions of the fundamental gap of Ge 1−x Sn x as a function of the total Sn-concentration: namely from an indirect to a direct gap, first, and the metallization transition at higher x. They also highlight the role of β-Sn in the reduction of the concentration range which corresponds to the direct-gap phase of this alloy, of interest for optoelectronics applications.

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Pushing the Composition Limit of Anisotropic Ge_1–xSn_x Nanostructures and Determination of Their Thermal Stability

et al. 2017

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Ge 1−x Sn x nanorods (NRs) with a nominal Sn content of 28% have been prepared by a modified microwavebased approach at very low temperature (140 °C) with Sn as growth promoter. The observation of a Sn-enriched region at the nucleation site of NRs and the presence of the low temperature -Sn phase even at elevated temperatures support a template-supported formation mechanism. The behaviour of two distinct Ge 1−x Sn x compositions with high Sn content of 17% and 28% upon thermal treatment has been studied and reveal segregation events occurring at elevated temperatures, but also demonstrate the temperature window of thermal stability. In situ transmission electron microscopy investigations revealed a diffusion of metallic Sn clusters through the Ge 1−x Sn x NRs associated with temperatures where the material composition changes drastically. These results are important for the explanation of distinct composition changes in Ge 1−x Sn x and the observation of solid diffusion combined with dissolution and redeposition of Ge 1−y Sn y (x>y) exhibiting a reduced Sn content. Absence of metallic Sn results in increased temperature stability by ~70 °C for Ge 0.72 Sn 28 NRs and ~60 °C for Ge 0.83 Sn 17 nanowires (NWs). In addition, a composition-dependent direct bandgap of the Ge 1−x Sn x NRs and NWs with different composition is illustrated using Tauc plots. ASSOCIATED CONTENT Supporting Information. Additional SEM, TEM, EDX and XRD data are provided. Moreover, a video for the phase separation in the TEM is supplied. This material is available free of charge via the Internet at http://pubs.acs.org.

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Non-substitutional Sn Defects in Ge1−x Sn x Alloys for Opto- and Nanoelectronics

Cited by 4 publications

References 8 publications

Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

The two gap transitions in Ge1−xSnx: Effect of non-substitutional complex defects

Pushing the Composition Limit of Anisotropic Ge_1–xSn_x Nanostructures and Determination of Their Thermal Stability

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Non-substitutional Sn Defects in Ge1−x Sn x Alloys for Opto- and Nanoelectronics

Cited by 4 publications

References 8 publications

Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1−xSnx films

The two gap transitions in Ge1−xSnx: Effect of non-substitutional complex defects

Pushing the Composition Limit of Anisotropic Ge1–xSnx Nanostructures and Determination of Their Thermal Stability

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Pushing the Composition Limit of Anisotropic Ge_1–xSn_x Nanostructures and Determination of Their Thermal Stability