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

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MBE Growth of Self-Assembled InAs and InGaAs Quantum Dots Embedded in Silicon Matrix which has been already introduced before for determination of local lattice distortions strain by geometric phase analysis, known as GPA strain (ε GP ii A ) and mathematically expressed by Eq. 5.8 [89]: ε ii = dmeasured InAs d bulk InAs − d bulk InAs (5.7) ε GP A ii = dmeasured loc − d measured ref d measured ref (5.8) The lattice mismatch f of Si/InAs system is expressed in-terms of the bulk lattice constants values of Si and InAs in Eq. 5.9: f = abulk InAs − abulk Si 6.055 − 5.431 = = 11.55 % (5.9) a bulk Si 5.431 The GPA strain mapping driven from HR-TEM image in Fig. 5.26 conrmed no detectable strain gradient in silicon matrix and fully relaxed InAs QDs, which is in agreement with the dark eld strain-contrast analysis in Fig. 5.25(c). Figure 5.26: GPA strain mapping of buried single InAs QD in the sample of 4 MLs InAs coverage embedded in Si Matrix. (a) HR-TEM cross-section image of a single InAs QD with 2 SFs. (b) ε GP xx A strain mapping in x direction conrmed almost fully relaxed InAs QD with no detectable strain gradient in Si matrix. (c) ε GP yy A strain mapping in y direction conrmed almost fully relaxed InAs QD with no detectable strain gradient in Si matrix. (TEM & strain performed@PDI-Berlin). One can used the last three equations (Eq. 5.7 - Eq. 5.9) to relate ε ii with ε GP A ii as shown in Eq. 5.11. The approximations used from the last observations are: 92
5.4 Self-Assembled InAs QDs Embedded in Si Matrix negligible strain relaxation (Eq. 5.10) and negligible crystal rotation. However, by direct substitution of the approximation in Eq. 5.10 into Eq. 5.11, the relation between material strain and GPA strain is obtained and expressed by Eq. 5.12: d bulk Si d measured Si = 1 (approximation) (5.10) ε GP A − f 1 + f = d measured InAs ( d bulk Si d measured Si d bulk InAs ) − d bulk Si (5.11) ε InAs = εGP A − f 1 + f (5.12) The material strain analysis of dierent shape and size InAs QDs is shown in Fig. 5.27. The direction and magnitude of tensile and compressive strain is clearly shown with the color map. The color scale indicates the type and magnitude of the strain. The tensile strain has positive sign values (marked in red to yellow colors in Fig. 5.27) and is pointing to outward directions (highlighted by red arrows). Fig. 5.27(a) shows an example of tensile strain in y direction (ε yy ). On the other hand, the compressive strain has negative sign values and marked in green to dark blue colors with direction (highlighted by red arrows) pointing to inward direction as illustrated in Fig. 5.27(b). The structure of 4 MLs InAs embedded in Si matrix proved to have high degree of relaxation and low residual strain values. The bulk lattice mismatch of 11.55 % is relieved by dislocation loops along the interface consisting of perfect 60 ◦ -type dislocations and partial dislocation with stacking faults inside the InAs clusters, which is in agreement with the literature [1]. By two-dimensional strain mapping derived from high-resolution TEM structure images, no strain gradients in the Si matrix around InAs clusters are detectable (Fig. 5.26). Therefore, it has been observed that the strain relaxation eects is mostly relieved by defects formation inside InAs QDs such as (SFs and MTs) and mist dislocation (MD) array at the InAs/Si interface, as it was shown in Fig. 5.27. On the other hand, anisotropic distortion of InAs lattice constant is another indication of strain relaxation. The residual strain is discussed based on the thermal mismatch between InAs and Si. However, the deformation force 93
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Molecular Beam Epitaxial Growth of
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Gutachter (Supervisors): 1. Prof. D
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patterns indicating a 2D smooth sur
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(MEE = migration enhance epitaxy) u
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viii
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CONTENTS 3.4.4 Planar Defects Assoc
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CONTENTS xii
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Introduction thesis a detailed stud
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Introduction 1.1.2 Thesis Approach
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Introduction 1.2 Thesis Outline The
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Theoretical Background of Semicondu
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Heteroepitaxial Growth of III-V Sem
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Page 56 and 57: Heteroepitaxial Growth of III-V Sem
Page 64 and 65: Experimental Growth and Characteriz
Page 78 and 79: MBE Growth of Self-Assembled InAs a
Page 118 and 119: MBE Growth of InAs and InGaAs Quant
Page 130 and 131: Optimization of MEE and MBE growth
Page 142 and 143: Conclusions substrates, respectivel
Page 144 and 145: REFERENCES [8] J. M. Gerard, O. Cab
Page 146 and 147: REFERENCES [29] http://www.wmi.badw
Page 148 and 149: REFERENCES [49] M. R. Brenner: GaP/
Page 150 and 151: REFERENCES [66] Y. Ishida, T. Takah
Page 152 and 153: REFERENCES [84] A. Garcia, C. M. Ma
Page 154 and 155: 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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