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 observed to have very low density compared to the InAs QDs and no detectable wetting layer has been detected in the rst measurement in TEM cross section image Fig. 5.12(a). Mist dislocations loops were observed to form at the InAs/Si interface consisting of perfect 60 ◦ -type dislocations and partial dislocation with SFs inside the InAs QDs observed to start moving from the dots to the Si surface (Fig. 5.12). Figure 5.12: TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 ML InAs QDs/ 50 nm Si cap/2 ML InAs) showing; (a) stacking faults defects start at InAs QDs running to the top surface; (b) HR-TEM of single InAs QD shows spherical to ellipsoidal QDs shape embedded in Si matrix and at shape InAs islands on the top layer of the grown structure; (c) HR-TEM of single InAs QD in Si matrix with 20 nm lateral size and 6 nm height the red arrows point to mist dislocation and the white arrow represents pure edge dislocation. (TEM performed@PDI-Berlin). The inuence of substrate o-cut has been found to have a strong impact on InAs dots shape and geometry. Depending on the dot diameter (D) dierent dot shapes were observed on exactly oriented substrates in case of InAs QDs grown with 2 MLs (Fig. 5.12(b)). They can be classied to: spherical shape when D < 10 nm, ellipsoidal shape, if 10 nm < D < 25 nm and plate-like shape when D > 25 nm. In contrast to that, a semi-coherent and multi-faceted InAs QDs with very homogeneous size distribution were observed in the sample of 2 ML InAs coverage embedded in Si matrix on mis-oriented Si substrates. A cross-section TEM image in Fig. 5.13(a) illustrates the very homogeneous and narrow size dots distribution with diameter D in the range of 5 - 8 nm. 78
5.4 Self-Assembled InAs QDs Embedded in Si Matrix Figure 5.13: TEM cross-section image of 2 MLs InAs QDs embedded in silicon matrix grown on 5 ◦ o-cut (100) substrate. (a) Dark eld cross section TEM image with narrow dots size distribution. (b) HR-TEM cross-section image with dierent dots shapes. (TEM performed@PDI-Berlin). The Moiré fringes pattern inside the dots in Fig. 5.13(b) reveal a good crystal quality of some dots, especially dots with more than one facet, hence spherical dots, seem to have more defects. Another interesting feature of the InAs islands on Si observed in Fig. 5.12(c) is the shift of the interface toward the InAs islands, and this interface is dened as the location where the extra half plane of dislocation is terminated. The interface shift has also been observed in the lower magnication TEM [17]. One possible explanation of a shift of 3 MLs Si to the InAs island in Fig. 5.12(c) is the interaction between dislocations and the inevitable ones parallel to the image plane [1]. The dislocations parallel to the image plane repel the ones to reach the interface. In this case the dislocations may be pinned above the interface and cause such a shift. The dislocations shown in Fig. 5.12(c) are not located precisely at the interface. If this is true, the precise location of the interface, which is a challenging subject in such nanometer scale structures, will have to be dened by a criterion rather than the location of dislocations [1]. 79
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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 42 and 43: 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
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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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