Strain and correlation of self-organized Ge 1-xMn x nanocolumns embedded in Ge (001) (original) (raw)
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Physical Review B, 2002
The growth of strained epitaxial self assembled nanocrystals is comprised of a variety of kinetic and thermodynamic factors that determine their morphology and size. Some of the significant factors to their stability are strain and interdiffusion. Here we directly measure the gradient of composition and strain in Ge nanocrystals grown on Si͑001͒ using anomalous x-ray scattering. By combining our x-ray results, where we relate strain, interdiffusion, and shape with atomic force microscopy measurements, we have been able to determine the complete strain configuration of these islands. We show that the amount of elastic energy in pyramids and domes can be evaluated. The transition from pyramids to domes is accompanied by an increase of lattice parameter and enhancement of interdiffusion, both leading to a drastic decrease of the elastic energy stored per atom.
Communications in Physics, 2014
By mean of molecular beam epitaxy (MBE) equipped with a reflexion high-energy electron diffraction (RHEED) technique, we have chosen an intermediate and appropriate substrate temperature of 130˚C to reproducibly synthetize high-TC Ge1−xMnx nanocolumns phase. Laser Pulse Atom Probe Tomography (LP-APT) technique have been used to determine at atomic scale the chemical composition inside nanocolumns and also in the surrounding diluted matrix. The Mn concentration inside nanocolumns is found to be highly inhomogeneous, it is about 20% at the bottom and can increase up to ∼40% in the top near the surface region. The Mn concentration in the matrix is about 0.25 % at the surface and can reach a highest value of ∼1% in regions close to the interface.
Formation and characterization of locally strained Ge1−xSnx/Ge microstructures
Thin Solid Films, 2014
In this study, we have examined the formation of uniaxially strained Ge microstructures with embedded Ge 1 − x Sn x epitaxial layers and the microscopic local strain structure in Ge and Ge 1 − x Sn x using synchrotron X-ray microdiffraction and the finite element method. We achieved local heteroepitaxial growth of Ge 0.947 Sn 0.053 layers on the Ge recess regions. Microdiffraction measurements reveal that an average uniaxial compressive strain of 0.19% is induced in Ge locally with Ge 1 − x Sn x stressors. In addition, we found that the Sn precipitation near the Ge 1 − x Sn x /Ge(001) interface occurs after post-deposition annealing at 500°C without the introduction of dislocation. It is considered that the local Sn precipitation occurs preferentially due to the larger residual stresses near the Ge 1 − x Sn x /Ge interface.
Growth competition between semiconducting Ge1−xMnx nanocolumns and metallic Mn5Ge3 clusters
Advances in Natural Sciences: Nanoscience and Nanotechnology, 2012
Structural and magnetic characterizations have been combined to investigate the growth kinetics of Ge 1−x Mn x diluted magnetic semiconductors (DMSs) on Ge(001) substrates by means of molecular beam epitaxy (MBE). We have identified the growth process window allowing stabilization of a high Curie temperature (T C ) nanocolumn phase and provide evidence that the growth of semiconducting Ge 1−x Mn x nanocolumns and metallic Mn 5 Ge 3 clusters is a competing process. Due to a continuous increase of the Mn concentration inside nanocolumns, induced by Mn segregation along the growth direction from the interface toward the film surface, nanocolumns become unstable when the Mn concentration reaches a value of ∼40 at.% then transform into Mn 5 Ge 3 clusters. We propose a real-time approach to realize stacked layers consisting of nanocolumns separated by a Ge barrier layer, allowing exploitation of the effect of giant magneto-resistance in multilayer structures
Fully coherent growth of Ge on free-standing Si(001) nanomesas
Physical Review B, 2014
We investigate the structural properties of Ge nanostructures selectively grown on Si. Defect-free nanostructures with a lateral size of 100 nm and surrounded by a thick (ß20 times larger than the coherent-film limit) Ge layer are achieved as demonstrated by transmission electron microscopy. As demonstrated by modeling based on elasticity theory solved by finite element methods, the peculiar combination of morphology and chemical composition of the nanostructures allows for a very efficient elastic relaxation of the heteroepitaxial strain. We demonstrate that, despite the relatively large size of the nanostructures, even a single dislocation would raise the energy of the system. A direct comparison between the strain field predicted by modeling and measured by energy-dispersive synchrotron-radiation grazing incidence x-ray diffraction shows substantial agreement.
Morphological and structural evolutions of diluted Ge[sub 1−x]Mn[sub x] epitaxial films
Applied Physics Letters, 2007
We investigate the structural and morphological evolutions of Ge 1−x Mn x films, grown by molecular beam epitaxy on Ge͑100͒, as a function of Mn nominal concentration ͑x͒. We show that in our experimental growth conditions ͑growth temperature T G ϳ 160°C͒, Mn atoms incorporated in the matrix increases with x up to a concentration m ϳ 0.03. Magnetic properties of the samples are mainly related to Ge 3 Mn 5 cluster phase, while transport properties are connected to Ge:Mn matrix.
Ge based nanostructures for electronic and photonic devices
Microelectronics Reliability, 2010
Self-assembled Ge x Si 1Àx islands were grown on Si(0 0 1) substrates by solid source molecular beam epitaxy. Two different morphological shapes with different sizes were evolved by tuning the growth time at a constant deposition temperature. Micro-Raman analysis was carried out to investigate the composition, intermixing and strain of resultant islands. The observed broad infra-red photoluminescence signal from grown samples was associated with radiative recombination of holes confined in the Ge islands and electrons localized in the Si buffer layer. The PL peak position and intensity were found to be influenced by the islands size and intermixing of Si and Ge. The electrical properties of the islands were studied through photoexcited I-V characteristics and current imaging using conducting mode atomic force microscopy.
X-ray analysis of strain, composition and elastic energy in Ge islands on Si(001)
International Journal of Nanotechnology, 2008
X-ray diffraction techniques have been extensively employed to study several structural and chemical properties of self-assembled islands. In this review we discuss recent results on Ge islands grown on Si(001). Grazing incidence diffraction is used to map the strain distribution of Ge pyramids and domes. By tuning the X-ray energy near the Ge K edge-to perform anomalous diffraction measurements-the chemical compositions of both types of islands were obtained. The data allow for direct evaluation of the elastic energy that is one of the crucial components for morphological evolution in this system. We then present a method to map out three-dimensional chemical and structural parameters in Ge domes. Finally, we discuss how such results can be combined to give new insights on growth mechanisms.