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 were kept xed and only the growth temperature was varied in the range of 400 − 500 ◦ C. Atomic force microscopy (AFM) images in Fig 5.6 shows that the InAs QDs density is slightly increased with increasing the growth temperature in the range of 400−450 ◦ C, while the QDs lateral dimensions (L) and average height (H av ) decreased from L = 33 - 55 nm and H av = 6.62 nm at 400 ◦ C (Fig. 5.6(a)) to values of L = 15 - 40 nm and H av = 4.5 nm at 450 ◦ C (Fig. 5.6(b)). The main reason for these changes are related to Indium desorption, which starts to be signicant at 450 ◦ C (Fig. 5.6(b)). This causes a reduction of the dot sizes at 450 ◦ C and do not allow any InAs nucleation at 500 ◦ C (Fig. 5.6(c)), which is in agreement with literature where no nano-islands formation are observed at temperatures higher than 450 ◦ C [3]. Figure 5.6: (1 × 1 µm 2 ) AFM images of 2 MLs InAs QDs grown using SK mode at dierent growth temperatures (a) 400 ◦ C, (b) 450 ◦ C, and (c) 500 ◦ C. 5.3.3.4 V/III Ratio In this investigation only V/III ratio values were varied. By increasing the V/III ratio from 15 to 35, the QDs density is strongly modied and increased from ∼ 10 8 cm −2 (Fig. 5.7(a)) to ∼ 10 11 cm −2 (Fig. 5.7(c)). AFM measurements show denser QDs for samples grown at higher As 4 pressures. The V/III ratio has a similar impact on the layer growth as the substrate temperature. Too high values 72
5.3 Results and Discussion shorten the migration length of the group III species, because they can nd a bonding partner more easily and the incorporation into the crystal is faster. The desorption of group III species can also be countered by the V/III ratio, which eectively shifts desorption temperatures [84, 34]. The sticking coecient is also dependent on the V/III ratio. Too low V/III ratio values on the other hand increase the migration length, but also the probability of desorption. Figure 5.7: (1 × 1 µm 2 ) AFM images of 2 MLs InAs QDs grown using SK mode with dierent V/III ratios: (a) 15, (b) 25, and (c) 35. In addition, metallic droplets of group III species can liquefy on the substrate surface, which results in lower temperature In desorption and lower density QDs formation. This is a clear indication that the As 4 ux is an important parameter to control the QDs density. 5.3.3.5 Indium Growth Rate In this investigation, the following growth parameters were used: 2 MLs InAs coverage, T G = 400 ◦ C and V/III ratio of 25 on n-doped Si (100) substrate. According to Fig. 5.8, the shape and size of InAs QDs are signicantly changed by increasing the In-growth rate from 108 nm/h (0.1 ML/s, Fig. 5.8(a)) to 324 nm/h (0.3 ML/s, Fig. 5.8(b)). It seems that a reduction of the formation time can switch the InAs QDs shape from circular to dashed-like InAs, this dash structures is preferentially oriented on [110] crystal direction. 73
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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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Page 36 and 37: Heteroepitaxial Growth of III-V Sem
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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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