Buried Dislocation Networks Research Articles

Displacement Fields Influence Analysis Caused by Dislocation Networks at a Three Layer System Interfaces on the Surface Topology

This work consists in a numerically evaluation of elastic fields distribution, caused by intrinsic dislocation networks placed at a nanometric trilayers interfaces, in order to estimate their influence on the surface topology during heterostructure operation. The organization of nanostructures is ensured by the knowledge of different elastic fields caused by buried dislocation networks and calculated in the case of anisotropic elasticity. The influence of elastic fields generated by induced square and parallel dislocation networks at CdTe / GaAs / (001) GaAs trilayer interfaces was investigated. By deposition, the nanostructures organization with respect to the topology was controled.

Directed self-organization of trenched templates for nanowire growth

We combine a proposed approach to fabricate self-organized nanowires, which are grown in trenched templates, with a periodic strain field of a buried misfit dislocation network or a compliant substrate to guide the kinetic roughening and coarsening process in the formation of the template. Numerical simulations of the directed self-organization process show the possibility to form perfectly ordered parallel trenches with adjustable period, which allows to grow extended nanowires.

Self-organized growth of Ni nanoparticles on a cobalt-oxide thin film induced by a buried misfit dislocation network

We report on a clear tendency toward organized growth, at room temperature, of Ni nanoislands deposited on a $\mathrm{CoO}(001)$ nanopatterned surface. The $9.2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ square surface patterning consists in a periodic displacement field induced at the surface by an underlying interfacial dislocations network that is buried at the interface between the $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick $\mathrm{CoO}(001)$ thin film and the $\mathrm{Ag}(001)$ substrate. Grazing incidence small and wide angle x-ray scattering (GISAXS and GIXD) performed in situ, during growth, reveal that the nucleation of Ni particles is driven by the underlaying dislocation distribution. The tendency for organization is confirmed by scanning tunneling microscopy (STM), which also reveals a quite narrow size distribution of the Ni nanoparticles around $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ width and $0.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ height.

Direct Wafer Bonding for Nanostructure Preparations

Direct Wafer Bonding has been widely developed and is very attractive for a lot of applications. Using original techniques based on direct bonding enable to carry out specific engineered substrates. Various illustrations are given among which twisted Si-Si bonded substrates, where buried dislocation networks play a key role in the subsequent elaboration of nanostructures.

Nano-structuration of CoO film by misfit dislocations

We have studied the nano-patterning of CoO film induced by misfit dislocation network at the interface with the Ag(0 0 1) substrate. Grazing incidence diffraction (GIXD), X-ray photoemission spectroscopy (XPS) and low energy electron diffraction (LEED) have been used to characterize chemistry and structure of the CoO layers. The XPS spectrum of the Co 2p core level permitted to establish the stoichiometric growth of CoO. The structure of the CoO film together with the absorption sites of cobalt and oxygen atoms was determined, thanks to GIXD measurements. Moreover we have followed the evolution of the in-plane lattice constant of the CoO as a function of the film thickness. It turns out that the CoO film growth starts with the same in-plane lattice constant of the Ag(0 0 1) substrate up to 3–4 ML; afterwards the in-plane parameter of CoO steadily increases before reaching a stable value of 2.98 Å at 23 ML. During the relaxation process, at about 8 ML of film thickness, we observe the formation of a buried misfit dislocation network. These dislocations, that have a period of 9.2 nm for a film thickness of 23 ML, induce mosaicity in the CoO film which then appears as a regular distribution of tilted domains.

Controlled Silicon (001) Surface Periodic Nanopatterning by Direct Wafer Bonding

In order to control simultaneously the nanostructures size, density and positioning, nanopatterned substrates are elaborated using an original process based on the revelation by preferential chemical etching up to the surface of a buried square dislocation network obtained by direct twist wafer bonding. By including the dislocation network into a SOI substrate thin film the surface patterning evolution during the selective chemical etching for 20 and 50 nm periodicity samples is controlled and checked by Scanning Electron Microscopy (SEM). A dislocation network periodicity dependent surface grating is showed. Si mesas with efficient aspect ratios are obtained after a second selective chemical etching allowing the further Ge islands self-assembled growth. Germanium growth equivalent to 10 Aå layer is performed at 600{degree sign} C on 50 nm periodicity nanopatterned surfaces. For different cooling rate from deposition temperature to room temperature the dots size, shape and density are characterized by Scanning Tunneling Microscopy and SEM.

Preparation of a nanopatterned surface of bonded silicon wafers using electrochemical thinning and chemical etching: A scanning tunnel microscopy investigation

Sacrificial anodic oxidation is used to thin silicon wafer bonding substrates. Chemical solutions, sensitive to the periodic strain field present in the upper ultra-thin silicon layer, are employed for selective etching. Subsequent scanning tunnel microscopy observations reveal a square array of trenches corresponding to the buried screw dislocation network initially formed at the bonding interface. The influence of the initial thickness and the annealing of the ultra-thin film on roughness and trench depth of the nanopatterned substrates are examined. Germanium growth experiments are performed in order to show the self-organization character of resulting structured surfaces.

Directed movement of Au–Si droplets towards buried dislocation networks on silicon bicrystals

Directed movement of Au–Si alloy droplets towards buried dislocation grids on a Si bicrystal has been observed by in situ ultrahigh vacuum transmission electron microscopy. It was found that once the underlying dislocation structure was dissolved, the movement of Au–Si droplets was directed to the region with remaining dislocation network. The migration of Au–Si droplets is driven by the energy difference between the strained bicrystal and nonstrained single-crystal silicon. The directed movement by the buried dislocation network is potentially significant in a wide range of technologies.

The challenges in guided self-assembly of Ge and InAs quantum dots on Si

The topic of guided self-assembly of Ge and InAs quantum dots on Si (001) substrates via epitaxy is discussed. A buried misfit dislocation network can be used to guide the assembly process through the associated strain field. Patterned substrates can also be used to guide the assembly process. This paper discusses the recent experimental and theoretical studies of the guided assembly process with an emphasis on what remains to be understood.

Self-Organized Growth of Nanoparticles on a Surface Patterned by a Buried Dislocation Network

The self-organized growth of Co nanoparticles is achieved at room temperature on an inhomogenously strained Ag(001) surface arising from an underlying square misfit dislocation network of 10 nm periodicity buried at the interface between a 5 nm-thick Ag film and a MgO(001) substrate. This is revealed by in situ grazing-incidence small-angle x-ray scattering. Simulations of the data performed in the distorted wave Born approximation framework demonstrate that the Co clusters grow above the dislocation crossing lines. This is confirmed by molecular dynamic simulations indicating preferential Co adsorption on tensile sites.

Dislocation networks adapted to order the growth of III‐V semiconductor nanostructures

We study by transmission electron microscopy shallowly buried dislocation networks (DNs). These DNs are grain boundaries (GBs) that form, between a thin GaAs layer and a GaAs substrate joined together by wafer bonding, in order to accommodate a tilt and a twist between these two crystals. These GBs are composed of a one-dimensional network of mixed dislocations and of a one dimensional network of screw dislocations (whereas a two-dimensional (2D) one is usually observed) forming hexagonal cells. These GBs generate a 2D surface pattern of dilatational and compressive strain adapted to the ordered growth of nanostructures which we demonstrate experimentally for GaAs and InGaAs nanostructures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanometric artificial structuring of semiconductor surfaces for crystalline growth

The coupling of standard self-organization methods with surface artificial nanostructuring has recently emerged as a promising technique in semiconductor materials to control simultaneously the size distribution, the density and the position of epitaxial nanostructures. Some physical aspects of the morphology and elastic strain engineering are reviewed in this article. The emphasis is on the effects of capillarity, growth rate anisotropy, strain relaxation and entropy of mixing for alloys. The interplay among these driving forces is first illustrated by III–V compound semiconductor growth on lithographically patterned surfaces, then by germanium growth on implanted substrates and nanopatterned templates obtained by chemical etching of buried strain dislocation networks. To cite this article: J. Eymery et al., C. R. Physique 6 (2005).

Buried dislocation networks for the controlled growth of III–V semiconductor nanostructures

Shallowly buried dislocation networks (DNs) can be used to organize the formation of epitaxial semiconductor quantum dots, via the periodic strain field induced at the growth front. We fabricate such DNs by bonding epitaxially two GaAs crystals twisted and tilted with respect to each other and studied them by transmission electron microscopy. The DNs differ greatly from the mere superposition of a square screw DN and of a one-dimensional mixed DN accommodating, respectively twist and tilt. We present a detailed quantitative analysis of these DNs and explain how their properties relate to the crystal disorientations. Dislocation interaction generates a surface pattern of dilatational and compressive strain favouring the ordered growth of (Ga)InAs nanostructures.

Germanium growth on nanopatterned surface studied by STM

A square surface nanopatterning is obtained by etching a buried dislocation network realised by a specific molecular bonding method. This template is used to organise the germanium quantum dot growth. The initial surface morphology as well as the quantum dot position and size are studied by scanning tunneling microscopy (STM). It is shown that the nanomesa roughness induces the dot nucleation, and therefore several dots (4–5) per mesa are obtained. These dots are coarsened to a single dot per mesa under ultra high vacuum annealing at 725 °C. Deep trenches between the mesas, controlled by the chemical etching solutions, prevent the formation of larger dots.

Buried dislocation networks designed to organize the growth of III-V semiconductor nanostructures

We first report a detailed transmission electron microscopy study of dislocation networks (DNs) formed at shallowly buried interfaces obtained by bonding two GaAs crystals between which we establish in a controlled manner a twist and a tilt around a k110l direction. For large enough twists, the DN consists of a twodimensional network of screw dislocations accommodating mainly the twist and of a one-dimensional network of mixed dislocations accommodating mainly the tilt. We show that in addition the mixed dislocations accommodate part of the twist and we observe and explain slight unexpected disorientations of the screw dislocations with respect to the k110l directions. By performing a quantitative analysis of the whole DN, we propose a coherent interpretation of these observations which also provides data inaccessible by direct experiments. When the twist is small enough, one screw subnetwork vanishes. The surface strain field induced by such DNs has been used to pilot the lateral ordering of GaAs and InGaAs nanostructures during metal-organic vapor phase epitaxy. We prove that the dimensions and orientations of the nanostructures are correlated with those of the cells of the underlying DN and explain how the interface dislocation structure governs the formation of the nanostructures.

Amorphization/recrystallization of buried amorphous silicon layer induced by oxygen ion implantation

In this paper we discuss the structural modifications observed in a buried amorphous Si (a-Si) layer containing high oxygen concentration level (up to ∼3 at. %) after being implanted at elevated temperature with O+16 ions. For implants conducted at temperatures lower than 150 °C, the a-Si layer expands via layer by layer amorphization at the front and back amorphous–crystalline (a–c) interfaces. When performed at temperatures above 150 °C, the implants lead to the narrowing of the buried a-Si layer through ion beam-induced epitaxial crystallization at both a–c interfaces. Cross section transmission electron microscopy analysis of samples implanted at 400 °C revealed an array of microtwins and a dislocation network band in the recrystallized material. In samples implanted at 550 °C, only a buried dislocation network band is observed.

Controlled surface nanopatterning with buried dislocation arrays

Self-assembled configurations of nanostructures are expected to play an increasing role in devices design, as an alternative to conventional microelectronics. The key limitation is the lack of control on localisation, density and size uniformity of the structures. Here we show how to create a template to overcome these problems. A periodic nanometre scale patterning can be induced at a silicon surface by buried dislocation networks obtained by twist wafer bonding, using stress selective etching of the surface. These templates are morphologically characterised by scanning tunnelling microscopy and grazing incidence X-ray diffraction. Stress fields and elastic energy densities are calculated for the non-etched solid, and the selective etching mechanisms are discussed. Germanium growth experiments on such a Si patterned surface give a demonstration of the ordering efficiency. This study provides a general method to create a template, which organises nanostructures with controlled periodicity over the full size of a Si wafer.

Grazing incidence x-ray scattering investigation of Si surface patterned with buried dislocation networks

Investigation of a surface patterned by buried dislocation networks is performed with grazing incidence x-ray scattering (GIXS). It is shown that surface long-range undulations lead to a azimuth-dependent diffusion spot, the scattering vector of which is mainly parallel to the x-ray propagation direction. This unusual scattering direction with GIXS is explained by the scales of the scattering objects. A geometrical model is proposed to extract the periodicity of the surface from GIXS.

Influence of a buried misfit dislocation network on the pyramid-to-dome transition size of Ge self-assembled quantum dots on Si(0 0 1)

The critical sizes of the pyramid-to-dome transition of Ge self-assembled quantum dots (SAQDs) grown on relaxed SiGe buffer layers were investigated for the relationship between the misfit strain built in dots and nucleation sites. The strain field of arrays of buried dislocations in a relaxed SiGe buffer layer provided preferential nucleation sites for quantum dots. Burgers vector analysis using plan-view transmission electron microscopy verified that the preferential nucleation sites of Ge SAQDs depended on the Burgers vector direction of corresponding dislocations. The measurement of the lateral distance between SAQDs and dislocations clarified that the location of SAQDs was at the intersection of the dislocation slip plane and the top surface. The samples are fabricated to contain low dislocation densities. The average dislocation spacing is larger than the surface migration length of Ge adatoms, resulting in two groups of SAQDs, those that are located along the dislocations, and those that are not. Atomic force microscopy observations showed a distinctively larger critical size for Ge SAQDs grown over the intersection of the dislocation slip plane and the top surface than those grown in regions between dislocations. These experimental observations indicate that the critical size of the pyramid-to-dome transition is strongly dependent on misfit strain in SAQDs with lower strain being associated with a larger critical size.

Ordering of Ge quantum dots with buried Si dislocation networks

Buried dislocation networks obtained by Si(001) wafer bonding pattern the free surface of the sample, giving rise to long-range undulations and short-range embossing, respectively, for flexion and rotation misalignement. Comparison with continuum-elasticity calculations reveals that this patterning is enhanced by strain-driven overetching. These surfaces are a template for growth, and we show that Ge quantum dots can be ordered with a fourfold symmetry by proceeding a postgrowth annealing.