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 The structure of 50 nm Si/2 MLs InAs/ 10 nm Si cap (without PGA) is shown in Fig. 5.15. The AFM image with surface roughness of 0.9 nm is illustrated in Fig. 5.15(a). However, the top surface of the grown structure dose not look perfectly connected. A high density of pits or (voids) with abrupt Si wall were observed, after capping with 10 nm of Si in both, SEM image in Fig. 5.15(b) as well as dark eld cross section TEM image in Fig. 5.15(c). The observation that InAs islands commonly occupy shallow depressions or (voids) shows that, during silicon overgrowth Si does not grow in the immediate vicinity of InAs islands. Figure 5.15: TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 MLs InAs /10 nm Si cap) showing; (a) (3 × 3 µm 2 ) AFM image of top surface with RMS value of 0.9 nm. (b) SE-SEM image with high density of voids, InAs islands prefer to locate in Si voids (magnied image) pointed with white arrow. (c) Dark eld cross-section TEM image of high density voids consistent with the SEM image. (TEM & SEM performed@PDI-Berlin). This observation has been also detected in similar structures [87]. A possible reason for this can be related to the highly strained InAs QDs and surface energies balance which will prevent the Si overgrowth on the top of the dots, leading to growth scenario in the areas between the dots forming the observed voids. Fig. 5.16(a) shows a cross-sectional HR-TEM image of InAs QD inside a Si void with abrupt walls. Geometric phase analysis (GPA) strain mapping in e yy and e xx directions Fig 5.16(b,c) conrmed highly strained QDs. In the third sample (Table 5.2), the rst PGA step was investigated at 700 ◦ C for 5 minutes for the structure of sample 2 (50 nm Si/2 MLs InAs /10 nm Si cap). The AFM image 82
5.4 Self-Assembled InAs QDs Embedded in Si Matrix Figure 5.16: TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 MLs InAs /10 nm Si cap); (a) HR-TEM cross-section of single Si void shows an InAs QD with preferential nucleation inside the void. (b) GPA strain mapping in e xx direction conrmed no clear wetting layer and strained QD. (c) GPA strain mapping in e yy direction and strained QD. (TEM & strain performed@PDI-Berlin). in Fig. 5.17(a) shows the PGA step has improved the surface roughness and RMS value from 0.9 nm (sample 2) to 0.23 nm (sample 3). However, one can observe Figure 5.17: TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 MLs InAs /10 nm Si cap) with PGA at 700 ◦ C. (a) (3 × 3 µm 2 ) AFM image of top surface with RMS value of 0.9 nm. (b) The dark eld cross-section TEM image shows the InAs QDs with disappeared wetting layer and shape transition. (c) HR-TEM cross-section image of localized circular-voids and V- SF above InAs QD. (TEM performed@PDI-Berlin). that the PGA step at 700 ◦ C has been found to have a signicance inuence on silicon surface reconstruction and Si atoms arrangement. An interesting Si surface 83
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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 46 and 47: Heteroepitaxial Growth of III-V Sem
Page 64 and 65: Experimental Growth and Characteriz
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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
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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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