Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

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Heteroepitaxial Growth of III-V Semiconductor on Silicon Substrates a lower additional energy barrier (E s ) to come down the edge to a lower terrace. From the mentioned kinetic parameters the diusion coecient is probably the most important parameters. It determines the average distance an atom can travel on at surface before being trapped. This distance is the surface diusion length (l D ) and can be dened by Eq. 3.6 [35]. l D = √ D s τ (3.6) Where τ is the residence time before re-evaporation. The surface diusion coef- cient is generally expressed as: D s = νa 2 exp ( −E A K B T ) (3.7) Where E A is the activation energy for diusion, ν is the attempt frequency and a is the characteristic jump distance. From Eq. 3.7 it is clear that deposition temperature is important because it controls the diusivity of the adaoms [35]. Therefore, the growth modes in real systems far from equilibrium will be controlled mostly by these kinetic factors and partially by the thermodynamics factors. Experimentally, the distinction between three classical growth modes is well known and classied to three growth regimes: Frank-van der Merwe (FM) (layers growth mode), Volmer-Weber (VW) (islands growth mode) and Stranski- Krastonov (SK) (mixed growth mode layers and islands) as illustrated in Fig. 3.2. In addition to the three well-known epitaxial growth modes mentioned above there is a fourth one, which is the step-ow growth mode as already mentioned in section (Sec. 3.2.1). The study of lm growth typically involves the deposition of a controlled amount of atoms onto a well characterized crystalline substrate at a prescribed set of growth conditions. In the case of Frank-van der Merwe (FM) (layer by layer growth mode): Layer growth is observed when the binding energy between the lm and substrate is stronger than the binding force between the lm particles. However, in this case a uniform monolayer of material is deposited in 2D forming a planar sheets as long as the the binding energy is decreased toward the bulk crystal value, the layer growth is sustained [36]. However, during FM growth mode a new layer is 28
3.2 The Concept of Epitaxy Figure 3.2: Schematic digram of the three fundamental growth modes: Frank-van der Merwe (FV) (layers growth mode), Volmer-Weber (VW) (islands growth mode) and Stranski-Krastonov (SK) (mixed growth mode layers and islands). Figure modied according to reference [36]. nucleated only after completion of the layer below, this growth occurs over long distances in ideal case. On other hand, when there is no strong bonding between lm and substrate, 3D-islands are being formed. The lm dose not wet the substrate because this will lead to an increase in the total surface energy. This growth mode is referred as Volmer-Weber (VW) growth mode, (see Fig. 3.2). It occurs when the binding force between the particles of the deposited material stronger than the forces between the material and the substrate. In heteroepitaxial growth, the so-called Stranski-Krastanov (SK) growth mode can occur. SK mode is considered as intermediate and kind of combination between the FM and VW growth modes, the above growth modes are merging in this case. It is caused by signicant lattice mist from lm and substrate. Here, the growth mode changes from layer by layer to island growth (see Fig. 3.2). During heteroepitaxial growth, the lattice mismatch between substrate and lm gives rise to biaxial strain, resulting in an elastic energy that grows with the increasing layer thickness. Mist dislocations at or near the substrate-lm interface will be formed if the layer thickness exceeds a critical thickness h c . At this thickness it is thermodynamically favorable to introduce dislocations because the elastic energy, released by the dislocations becomes comparable to the increase in the interfacial 29
Page 1: Molecular Beam Epitaxial Growth of
Page 4 and 5: Gutachter (Supervisors): 1. Prof. D
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Page 12 and 13: CONTENTS 3.4.4 Planar Defects Assoc
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Page 16 and 17: Introduction thesis a detailed stud
Page 18 and 19: Introduction 1.1.2 Thesis Approach
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MBE Growth of Self-Assembled InAs a
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MBE Growth of InAs and InGaAs Quant
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Optimization of MEE and MBE growth
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Conclusions substrates, respectivel
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REFERENCES [8] J. M. Gerard, O. Cab
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REFERENCES [29] http://www.wmi.badw
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REFERENCES [49] M. R. Brenner: GaP/
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REFERENCES [66] Y. Ishida, T. Takah
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REFERENCES [84] A. Garcia, C. M. Ma
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REFERENCES [100] M. Felici, P. Gall
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REFERENCES [116] H. Usui, H. Yasuda
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REFERENCES [133] Grassman, T. J. Br
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Conferences Contributions: Tariq Al
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Nomenclature
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REFERENCES symbol Descriptions γ f
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like to thank all member of the Ins
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REFERENCES Erklärung Hiermit versi
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Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

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