Competing relaxation mechanisms in strained layers

Tersoff, J.; LeGoues, F. K.

doi:10.1103/physrevlett.72.3570

Cited by 771 publications

(451 citation statements)

References 33 publications

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“…There is theory for island formation that emphasizes nucleation. It suggests that islands must overcome an energy barrier associated with a critical size so that the elastic energy gained can balance the extra surface energy cost [11]. The theory is reasonably consistent with experiments at relatively high misfit.…”

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confidence: 70%

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Fast Kinetic Monte Carlo Simulation of Strained Heteroepitaxy in Three Dimensions

2008

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Accelerated algorithms for simulating the morphological evolution of strained heteroeptiaxy based on a ball and spring lattice model in three dimensions are explained. We derive exact Green's function formalisms for boundary values in the associated lattice elasticity problems. The computational efficiency is further enhanced by using a superparticle surface coarsening approximation. Atomic hoppings simulating surface diffusion are sampled using a multi-step acceptance-rejection algorithm. It utilizes quick estimates of the atomic elastic energies from extensively tabulated values modulated by the local strain. A parameter controls the compromise between accuracy and efficiency of the acceptance-rejection algorithm. PACS numbers:Epitaxial growth techniques enable deposition of a dislocation-free thin film on a substrate of a different material with a mismatched lattice constant. For film-substrate combinations such as Ge/Si, InAs/GaAs and InAs/InP, arrays of three-dimensional (3D) coherent islands self-assemble spontaneously beyond certain film thicknesses under appropriate growth conditions [1,2,3,4]. These studies are of much current interest since they are expected to find applications in future microelectronic devices.One of the most widely studied examples is Ge/Si(100) with a 4% lattice misfit. Relatively flat islands called pre-pyramids start to emerge at 3 monolayers (MLs) of Ge coverage [5,6,7]. Upon further deposition, they quickly grow into truncated pyramids bounded by four (105) facet planes on the sides and subsequently into fully grown pyramids which are also called hut islands. Upon still further deposition, they become dome islands bounded mainly by (113) facet planes. Finally, large dislocated islands appear. For the closely related alloy variant Si 1−x Ge x /Si(100) with a generally lower 4x% misfit, the development is rather similar and goes through stages characterized by ripples, hut islands, dome islands and finally dislocated islands [8,9,10]. The structures are however larger and each transition is postponed to occur at a larger film thickness. The islands are also more closely packed.Islands self-assemble because they can relieve the elastic stress in the heteroepitaxial films. There is theory for island formation that emphasizes nucleation. It suggests that islands must overcome an energy barrier associated with a critical size so that the elastic energy gained can balance the extra surface energy cost [11]. The theory is reasonably consistent with experiments at relatively high misfit. At low misfit, the critical island size and hence the energy barrier are expected to increase and make nucleation prohibitively difficult. Island formation mechanisms which do not have a barrier then offer a more promising explanation. For example, according to the Asaro-Tiller-Grinfeld (ATG) theory [12,13,14], strained surfaces are unstable at sufficiently long wavelengths. Therefore, shallow ripples first develop from small random initial perturbations and then into islands. For this mechanism to oper...

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confidence: 70%

“…More importantly, it is exact for arbitrary morphologies. This is in sharp contrast to half-space Green's functions in the small slope approximation which are often applied [11,26,27].…”

Section: Exact Green's Function Methodsmentioning

confidence: 98%

Fast Kinetic Monte Carlo Simulation of Strained Heteroepitaxy in Three Dimensions

2008

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“…It is obvious that the formation of 3D islands allows the reduction of strain energy in the Ge layer and therefore the islands are at least partially relaxed. 18,[29][30][31][32] From the measurement of inplane strain in coherent Ge islands on Si͑001͒ by TEM after deposition of 11 ML Ge at 600°C by CVD using GeH 4 it was deduced that no significant in-diffusion of Si has occured and that a strain relaxation of the island of up to 84% has taken place. 30 Other authors report of a Si content of 40% in capped islands deposited at 750°C.…”

Section: Electroluminescence Of 3d Islandsmentioning

confidence: 99%

Size distribution and electroluminescence of self-assembled Ge dots

Vescan

Stoïca

Chretien

et al. 2000

Journal of Applied Physics

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In this article we study the electroluminescence of p-i-n diode structures with Ge dots consisting of coherent three-dimensional small ͑pyramids͒ and larger ͑dome͒ islands. The Ge dots are formed through strain-induced islanding. The diode structures, including one layer with Ge dots, were deposited on Si mesas with variable areas in order to study the influence of limited area deposition on self-assembling. It was observed that the reduction of deposited area improves island uniformity. The combined analysis of island distribution and electroluminescence spectra has lead to the conclusion that domes in small diodes have a smaller Si content or are less relaxed than domes in larger diodes. The diodes are found to emit up to room temperature near the optical communication wavelength of 1.3 microns.

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“…22 Introduction of dislocations in the flat islands is a competing strain relief mechanism to the surface roughening. 18 This mechanism is rather effective under the growth conditions employed in this work, despite the fact that in a highly strained Ge/Si͑111͒ system the nucleation of 3D islands represents the dominating strain relieving mechanism. 18 In the flat islands, strain energy is relieved to great extent by the dislocation network.…”

mentioning

confidence: 99%

“…Under such conditions, the strained growth system minimizes the total free energy by forming 3D islands, a process called strain relieving surface roughening. 18 In and around the islands the strain energy is decreased by elastic strain relief, overweighing the increase of the surface free energy due to the increased surface area. Formation of strain relieving 3D islands is a fast, many particle process as observed in real time STM observations.…”

mentioning

confidence: 99%