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 and V-SF formation above and around the InAs QDs have been observed after the rst PGA cycle at 700 ◦ C. Nevertheless the QDs in Si voids will also evaporate, but the vapor is conned in the voids, evolved nally to nearly spherical QD shape. A further Si capping at 700 ◦ C has inuence on Si surface reconstruction and circular-voids kinetics. A localized circular-voids formation above the semi-coherent InAs QDs layer only has been observed after the nal Si capping step. The second PGA cycle at 800 ◦ C proved to have strong impact on circularvoids kinetics and Si growth quality, through total re-crystallization and melting of the whole structure and new atomic arrangement. A high quality (defect-free) Si matrix growth with voids and V-SF free has been observed after the second PGA cycle at 800 ◦ C conrming the proposed growth model in Fig. 5.21. Strain analysis conrmed almost fully relaxed QDs. However, These QDs are relaxed via the creation of mist dislocation loops that are restricted in the InAs/Si interface region, whereas the Si matrix is (extended) defect-free and with no detectable strain gradient. However, in some cases few SFs and MTs are observed to form only inside the dots. The inuence of InAs coverage has been investigated with 1 ML, 2 and 4 MLs nominal thicknesses grown on 5 ◦ ocut Si (100) substrate. Fig. 5.22 shows the cross-section HR-TEM images of embedded InAs QDs in silicon matrix with dierent InAs nominal thicknesses. A clear size, density, and shape evolution has been observed in this study. The cross-section HR-TEM image in Fig. 5.22(a) with low InAs coverage of 1 ML shows a small at-coherent InAs QDs. This observation led to further strain and optical studies as shown in Fig. 5.23 and Fig. 5.24. A further increase in InAs QDs coverage to 2 MLs resulted in a very homogeneous size distribution (5-8 nm) and spherical to faceted QDs shape formation (Fig. 5.22(b)). The deposition of 4 MLs InAs QDs found to have a signicant inuence on density, size and shape of the QDs. A high density of semi-coherent InAs QDs with dierent shapes and wider dots size distribution (8-20 nm) has been observed compared to low InAs covearge of 1 ML. However, other authors reported a larger and more dislocated InAs clusters compared to our observation in this investigation [88]. Fig. 5.22(c) illustrates a HR-TEM image of a semicoherent single QD with lateral size of 18 nm observed in 4 MLs InAs sample. 88
5.4 Self-Assembled InAs QDs Embedded in Si Matrix Figure 5.22: Cross-section HR-TEM images of embedded InAs QDs in silicon matrix with dierent InAs coverage grown on 5 degree miscut Si(100) substrates. (a) 1 ML (small at-coherent QDs). (b) 2 MLs (spherical to faceted dots shape). (c) 4 MLs (single semi-coherent QD). (TEM performed@PDI-Berlin). Geometric phase analysis (GPA) strain mapping with 1 ML InAs coverage (Fig. 5.23(b)) proved the existence of coherent InAs layer on top of a highly Figure 5.23: TEM cross-section image of InAs/Si QDs sample (50 nm Si/1 ML InAs /10 nm Si/40 nm Si cap) on 5 ◦ o-cut substrate showing; (a) HR-TEM cross section image, shows at coherent InAs QDs marked with yellow color; (b) GPA strain mapping of area in yellow rectangle, in-plane GPA strain (e xx ), gradient along growth direction up to 0.5 %, while out-of-plane GPA strain (e yy ), only near the surface and up to 10 % (white arrows), coherent InAs wetting layer on top of highly strained silicon. (TEM & strain performed@PDI-Berlin). 89
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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 52 and 53: Heteroepitaxial Growth of III-V Sem
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Page 130 and 131: Optimization of MEE and MBE growth
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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
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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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