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 Figure 6.6: (a) The schematic sequence of the growth of GaAs/In 0.15 Ga 0.85 As/GaAs nanostructure. (b) and (c) The two dimensional AFM images (5×5 µm 2 ) showing the surface morphology after the growth of a GaAs buer alone and GaAs/In 0.15 Ga 0.85 As/GaAs complete structure, respectively. (d) A 3D-view of the whole grown structure showing the height of highly localized dome-like structures in the nano-holes. (e) A 36 ◦ tilted SEM image showing the cross section of the GaAs/In 0.15 Ga 0.85 As/GaAs QDs structure localized in the patterned holes [120]. controlled nature of growth after the full GaAs/In 0.15 Ga 0.85 As/GaAs nanostructure. The AFM prole of this sample (Fig. 6.6(c,d)) however exhibits that after the growth of the GaAs capping layer additional nano-crystallites are formed in between the holes causing high surface roughness of about 2-3 nm. We believe that these additional nano-crystallites are formed during the deposition of the GaAs capping layer at 500 ◦ C due to the smaller migration length of Ga ad-atoms at such low growth temperatures. The patterned holes on the silicon surface have a slight variation of 5-10 nm in the diameter of the nanoholes, therefore, this variation in diameter of the patterned holes results in the variation of 112
6.3 Further Results: Site-Controlled Growth of InGaAs QDs Embedded in GaAs Matrix on Pre-Patterned Silicon Substrate size of nucleated QDs during the MBE growth. The uctuation of beam uxes during the growth could also partially contribute to the non-uniformity of the nucleated QDs. The lack of nucleation of QDs in some of the holes could be due to the surface degradation after the processing steps, the local surface inhomogeneities would aect the diusion of ad-atoms to certain crystal directions, which would result in a non-uniform distribution of nucleation sites during the growth. A tilted scanning electron microscope image (Fig. 6.6(e)) displays the cross section of the QDs localized in the patterned holes obtained after cutting through the localized QDs with focused ion beam (FIB). The cross sectional view exhibits a good interface between QDs and silicon in the patterned hole. The selective formation of GaAs/ In 0.15 Ga 0.85 As/GaAs nanostructures inside the patterned holes with 1 µm spacing after dierent stages of the growth can be explained based on the lower chemical potential inside the etched holes than the plane surface [121]. This gradient of chemical potential provides the driving force for the group-III ad-atoms to diuse to the holes and preferentially nucleate there [121, 122]. The growth of GaAs/InAs/GaAs nanostructures on pre-patterned Si masked with SiO 2 has been demonstrated in reference [12] with thick nominal depositions. But we have demonstrated here for the rst time the site-controlled growth of GaAs/In 0.15 Ga 0.85 As/GaAs nanostructures with very low nominal deposition thicknesses directly on pre-patterned Si without the use of SiO 2 masks. These results are highly encouraging for the realization of III/V optical devices on the pre-patterned Si surfaces for potential applications. 113
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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 76 and 77: 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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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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