Evolution of coherent islands in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Si</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi>−</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ge</mml:mi></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mo>/</mml:mo><mml:mi mathvariant="normal">Si</mml:mi><mml:mo>(</mml:mo><mml:mn>0

Floro, Jerrold A.; Chason, E.; Freund, L. B.; Twesten, R. D.; Hwang, R. Q.; Lucadamo, G.

doi:10.1103/physrevb.59.1990

Cited by 156 publications

(124 citation statements)

References 34 publications

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“…Since these ridges are less effective in relaxing the misfit strain when compared with threedimensional islands, they are formed as a result of kinetic constraints. A similar kind of island growth and coalescence phenomenon has been reported by Floro and coworkers 14,19 during low temperature growth of SiGe films. Their in situ stress measurements show that the average strain in the film, which initially decreases due to the formation of 3D islands attains a minimum beyond which the instantaneous stress increases due to formation of ridge like structures shown in Fig.…”

Section: Figmentioning

confidence: 62%

“…The ridges that we observe in our simulations closely resemble the kinetically limited structures observed in recent experiments of Floro and co-workers. 14 ͑3͒ Numerical studies are also conducted to identify potential mechanisms of island coarsening-we find that both contact-coarsening as well as Ostwald ripening are possibly operative in dense island arrays.…”

Section: Introductionmentioning

confidence: 99%

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Three-dimensional simulations of self-assembly of hut-shaped Si–Ge quantum dots

Ramasubramaniam

Shenoy

2004

Journal of Applied Physics

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Optical properties of multi-stacked InGaAs/GaNAs quantum dot solar cell fabricated on GaAs (311)B substrate J. Appl. Phys. 112, 064314 (2012) Optical polarization properties of a nanowire quantum dot probed along perpendicular orientations Appl. Phys. Lett. 101, 111112 (2012) Electroluminescence from quantum dots fabricated with nanosphere lithography Appl. Phys. Lett. 101, 103105 (2012) Nucleation features and energy levels of type-II InAsSbP quantum dots grown on InAs(100) substrate Appl. Phys. Lett. 101, 093103 (2012) Highly luminescing multi-shell semiconductor nanocrystals InP/ZnSe/ZnS Appl. Phys. Lett. 101, 073107 (2012) Additional information on J. Appl. Phys. This article presents the results of three-dimensional modeling of heteroepitaxial thin film growth with the objective of understanding recent experiments on the early stages of quantum dot formation in SiGe/Si systems. We use a continuum model, based on the underlying physics of crystallographic surface steps, to study the growth of quantum dots, their spatial ordering and coarsening behavior. Using appropriate parameters, obtained from atomistic calculations, the ͑100͒ orientation is found to be unstable under compressive strains. The surface energy now develops a minimum at an orientation that may be interpreted as the ͑105͒ facet observed in SiGe/Si systems. This form of the surface energy allows for the growth of quantum dots without any barrier to nucleation-dots are seen to start off via a surface instability as shallow stepped mounds, which steepen continuously to reach their low energy orientations. During the very initial stages of growth, mounds are seen to grow in a dense array with several of them impinging on each other and subsequently coalescing to form larger mounds. This behavior occurs due to the competition between surface energy which seeks to minimize the free-energy by the formation of islands with side-walls at the strain stabilized orientations and repulsive elastic interactions between such closely spaced islands. Using simple analytical calculations, we show the existence of a critical island size for this coalescence behavior. A key result of our analysis is the inverse scaling of this critical size with the misfit strain in the film. While energetic analyses may be used to obtain useful insights, the growth of quantum dots is essentially a nonequilibrium process and requires a fundamental understanding of the kinetics. Numerical studies show that the growth kinetics has a profound effect on surface morphology: arrays of well-separated islands or, alternatively, intersecting ridges are obtained in different kinetic regimes. We also study an alternative model of a stable but nonfacet ͑100͒ orientation and point out the inconsistencies of this assumption.

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Section: Figmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Three-dimensional simulations of self-assembly of hut-shaped Si–Ge quantum dots

Ramasubramaniam

Shenoy

2004

Journal of Applied Physics

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“…With the growth of the island, misfit strain builds up. The strain energy can be reduced in four ways: ͑i͒ by increasing the height to base diameter aspect ratios of the islands; 7,24,25 ͑ii͒ by the introduction of misfit dislocations at the interface. This requires high strain and occurs only for the larger islands; ͑iii͒ by lowering the misfit between the island and the substrate which could result from the alloying of Si into the Ge island; and ͑iv͒ by reorienting the interface to accomplish partial detachment of the island, thereby lowering the strain energy.…”

Section: Figmentioning

confidence: 99%

Strain relaxation by alloying effects in Ge islands grown on Si(001)

et al. 1999

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Transmission electron microscopy is used to study the morphology and the composition profile of ''pure'' Ge islands grown at high temperature on Si͑001͒ by molecular beam epitaxy. An alloying process, involving mass transport from the substrate to the islands during the island growth, was identified. It was found that, as a result of Si mass transport to the Ge islands, the island/substrate interface moves towards the substrate, and trenches form on the substrate surface around the islands. Reduction of the misfit strain at the island/substrate interface is the driving force for this process. ͓S0163-1829͑99͒00748-1͔Semiconductor quantum dots ͑QD's͒ are attracting increasing interest because of their significant optoelectronic properties. 1 Although QD's can be produced in many ways, the method of coherent island formation is of great importance for materials with large lattice mismatch ͑such as Ge͑Si͒/Si 2,3 and In x Ga 1Ϫx As/GaAs 4 because of the possible combination of the QD growth and semiconductor integration techniques. Of crucial importance in determining the optoelectronic properties of the QD's are the structural parameters of the QD's including the shape, size and composition. 5 Uniformity in and control over these parameters are a prerequisite for many applications. To achieve this goal, a complete understanding of the mechanism of the QD growth is necessary. Although many investigations have concentrated on the shape and size 6,7 and evolution 8,9,10 during the QD growth, relatively less attention has been paid to the composition. 11,12,13 In the classical Stranski-Krastanow 14 ͑S-K͒ mode of coherent island formation, one material with a different lattice parameter and low interfacial energy is initially deposited on a substrate surface, layer by layer, forming a ''wetting layer''. When the wetting layer reaches a critical thickness ͓usually three to five monolayers for pure Ge on Si͑001͒, 3,15 island growth starts to partially release the mismatch strain energy between the epitaxial layer and the substrate. However, in the case of InAs/GaAs, recent investigations suggest that, for higher temperature growths, there is significant mass transport from both the wetting layer and the substrate to the islands. 16 Furthermore, the wetting layer in InAs/GaAs systems has been reported to be an ͑In,Ga͒As alloy with temperature dependent composition. 17 The composition of the alloy wetting layer will certainly affect any subsequent island growth procedure. These points suggest that the classical S-K growth mechanism needs to be modified to explain the details of island growth. In this paper, we demonstrate evidence for mass transport from the Si substrate to the Ge islands during high temperature molecular beam epitaxy ͑MBE͒ growth of ''pure'' Ge islands on the Si͑001͒ substrate. The mass transport changes the composition of the islands, moves the Ge/Si interface below the original substrate surface, and forms a trench around each island. It is proposed that the driving force for this mechanism is a reduction...

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“…4,5 The experiments carried out so far demonstrated a variety of possible island morphologies of different height-to-base aspect ratio ͑ar͒: prepyramids or mounds ͑arϽ 0.1͒, 6,7 shallow pyramids ͑ar= 0.1͒ or rectangular huts bounded by ͕105͖ facets, 5,8 dome-shaped multifaceted islands ͑ar= 0.22 -0.26͒, 5,9 or even steeper ͑ar= 0.26-0.32͒ barn-shaped morphologies. 10 A simple explanation for this sequence of island shapes, which involves a progressive increase in the ar, occurring with increasing island volume V, can be offered by comparing the energy of an island with that of the WL.…”

Section: Introductionmentioning

confidence: 99%

Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset

et al. 2009

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The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer ͑WL͒ of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understanding of island growth with deposition. In order to investigate the actual onset of three-dimensional islanding and the critical WL thickness in the Ge/Si͑001͒ system, a key issue is controlling the Ge deposition with extremely high resolution ͓0.025 monolayer ͑ML͔͒. Atomic force microscopy and photoluminescence measurements on samples covering the deposition range 1.75-6.1 ML, taken along a Ge deposition gradient on 4 in. Si substrates and at different growth temperatures ͑T g ͒, surprisingly reveal that for T g Ͼ 675°C steeper multifaceted domes apparently nucleate prior to shallow ͕105͖-faceted pyramids, in a narrow commonly overlooked deposition range. The puzzling experimental findings are explained by a quantitative modeling of the total energy with deposition. We accurately matched ab initio calculations of layer and surface energies to finite-element method simulations of the elastic energy in islands, in order to compare the thermodynamic stability of different island shapes with respect to an increasing WL thickness. Close agreement between modeling and experiments is found, pointing out that the sizeable progressive lowering of the surface energy in the first few MLs of the WL reverts the common understanding of the SK growth onset. Strong similarities between islanding in SiGe and III/V systems are highlighted.

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Evolution of coherent islands inSi1−xGex/Si(0

Cited by 156 publications

References 34 publications

Three-dimensional simulations of self-assembly of hut-shaped Si–Ge quantum dots

Three-dimensional simulations of self-assembly of hut-shaped Si–Ge quantum dots

Strain relaxation by alloying effects in Ge islands grown on Si(001)

Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset

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