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

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MBE Growth of InAs and InGaAs Quantum Dots Embedded in GaAs Matrix technique to fabricate features in the sub-100 nm and in some cases even sub-10 nm range [119]. In this section, the MBE growth of QDs on optimized patterned Si surface with highly selective formation of localized dome like nanostructures in patterned holes will be discussed in details. 6.3.1 Experimental Details Exactly oriented n-type Si (100) substrates were used for patterning processes. After optimized wet and dry etching recipes, the silicon substrates with subnano holes were patterned using e-beam technique [120]. The substrate was further cleaned in IPA at 80 ◦ C for 10 min and in oxygen plasma asher for 30 min to remove any residual resist particles and carbon contamination left after the lithographic processing. Finally, the substrate was cleaned with HF:H 2 O (1:2) solution for two minutes to remove the native oxide. The substrates were loaded into a Varian Gen II molecular beam epitaxy (MBE) system within 10 min of ex-situ chemical cleaning. During the growth of GaAs/ InGaAs/GaAs nanostructures, the growth rate of gallium was 0.75 ML/s and of indium 0.13 ML/s, respectively. The beam equivalent pressure (BEP) for gallium and indium were 2×10 −7 Torr and 9×10 −8 Torr, respectively, and the arsenic BEP throughout the growth was 5 × 10 −6 Torr. The V/III ratio was adjusted to about 20 for all growth runs. 6.3.2 Characterization of Pre-Patterned Si Substrates The advantage to use positively tapered sidewalls nano-holes is the possibility to create multi-facets hole surface prole with dierent crystal orientations. However, this in turn could lead to a new way of lattice adjustment with the chance to get defect-free nanostructures. In order to achieve sub-100 nm holes with controlled diameter and shape on the Si substrate, the electron beam lithography process parameters for single pixel dot exposure were optimized [120]. Using an optimized electron beam lithography and dry etching recipes, the Si substrates were patterned with square lattices of sub-100 nm holes with various periods ranging from 1 µm down to 200 nm. Fig. 6.3 shows the SEM prole of the patterned Si substrate for nano-holes with dierent spacing. The surface 108
6.3 Further Results: Site-Controlled Growth of InGaAs QDs Embedded in GaAs Matrix on Pre-Patterned Silicon Substrate Figure 6.3: The SEM prole of the Si surface patterned with dierent holes periods, (a) 1 µm. (b) 750 nm. (c) 500 nm. (d) 200 nm. morphology and the depth of the patterned holes were investigated by AFM Fig. 6.5(a). The diameter and the depth of the patterned holes both ranged between 60 and 70 nm giving an aspect ratio equal to unity conrmed by a single hole high resolution atomic force microscopy measurement. 6.3.3 MBE Growth of GaAs/In 0.15 Ga 0.85 As/GaAs Quantum Dots on Pre-Patterned Silicon Before the epitaxial growth of pre-patterned Si with III/V material, the surface was cleaned in-situ in the MBE system to remove the carbon contamination and native oxide deposited on the surface during the loading process. The atomic hydrogen (AH) cleaning has been proposed in the literature to remove organic contaminants [81, 5]. We followed this approach by exposing the Si surface to an AH ux of 3 × 10 −7 Torr at 500 ◦ C for 45 min. In the next step the sample was annealed at 850 ◦ C for 10 min to desorb the native oxide from the surface. 109
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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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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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Experimental Growth and Characteriz
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Page 72 and 73: Experimental Growth and Characteriz
Page 78 and 79: MBE Growth of Self-Assembled InAs a
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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
Page 156 and 157: REFERENCES [116] H. Usui, H. Yasuda
Page 158 and 159: REFERENCES [133] Grassman, T. J. Br
Page 160 and 161: Conferences Contributions: Tariq Al
Page 162 and 163: Nomenclature
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