Kinetic and Strain-Induced Self-Organization of SiGe ...

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22 CHAPTER 2. MOLECULAR BEAM EPITAXY (MBE) Figure 2.6: Critical thickness versus Ge-content for Si1−xGex on Si [68]. � Source: MBE Matthews-Blakeslee.jpg epitaxial crystal growth. In our case the Si-substrates have undergone several precursor processing steps and have been exposed to air. Thus, the Si-surface is covered with metallic or organic impurities or just the amorphous natural silicon-dioxide SiO2. On a slightly contaminated surface epitaxial growth would be inhibited or at least the properties of the epilayers – electrical, optical or structural – would be poor. Without oxide desorption the growth on Si-wafers that are covered by an amorphous SiO2 layer (natural oxide (∼ 20 ˚A) or chemical oxide caused by the cleaning procedure (RCA: ∼ 60 ˚A)) would produce amorphous Si epilayers. In the following sections some relevant cleaning procedures are discussed [53]. 2.2.1 Pre-Cleaning Small substrate-pieces that have been processed before (especially the etched wire substrates, Ch. 7) are successively cleaned in Trichloretylen, Acetone, Methanol using an ultrasonic bath (US), 5 min per step. After that the substrates are rinsed with deionized water (DI- H2O) and dried using the flow of a nitrogen (N2) nozzle. Additionally, the Si-pieces are cleaned with sulphuric acid (H2SO4, 96%) and hydrogen peroxide (H2O2, 30%) for 15 min at
2.2. CLEANING PROCEDURE 23 H2SO4 : H2O2 = 5:1. In this acidic cleaning step organic impurities on the surface are oxidized and removed. This cleaning procedure closes with rinsing the samples in DI-H2O for another 15 min. 2.2.2 RCA-Cleaning The RCA-cleaning procedure is again a multi-step procedure that provides extraordinary clean surfaces and makes good crystalline quality of the epilayers possible. Although the cleaning sequence that has been developed by the Radio Corporation of America [71, 72] is time consuming, the good results (much better than with a short HF-Dip) speak for themselves. In the first part of the cleaning procedure the Si-substrates are lowered into a boiling alkaline bath (80 ◦ C) for 15 min. Subsequently the pieces are rinsed in a DI-H2O water-bath for another 15 min or at least till the resistivity extends values of 10–15 MΩcm. In the second part the substrates are immersed in an acidic mixture (80 ◦ C) for 15 min. Afterwards, in the final step, the pieces are rinsed again in the DI-H2O water-bath for 15 min to wash away residual ions of the acid. For better handling the pieces are kept during the whole RCA- cleaning procedure in a polypropylene basket. Small pieces (17.5 mm × 17.5 mm) are cleaned in quartz glasses standing in a temperature regulated water-bath. Whole 4”-Si-wafers are cleaned in suitable quartz basins and are handled with special clamp-holders. The alkaline mixture consists of NH3 (25%), H2O2 (31%) and DI-H2O in parts of 1:1:5. HCl (30%), H2O2 (31%) and DI-H2O in parts of 1:1:5 are the ingredients of the acid. Whereas the acid removes organic impurities, the basic bath should take away metallic contamination. Although the original recipe for RCA-cleaning includes three HF-Dips (in the beginning, after the acidic and the alkaline treatment) in our ”HF-free RCA-cleaning” procedure no HF-Dip is implemented. Hence, this variation of RCA-cleaning generates a chemical oxide with a thickness of some tens of ˚Angstroms and a hydrophilic substrate surface. [53] 2.2.3 HF-Dip An HF-Dip is used to remove the natural SiO2 from the Si-substrate surface immediately before the Si-pieces or Si-wafers are put into the load-lock chamber. Usually an HF-Dip is a mixture of HF (40%) and DI-H2O with a ratio between 1:5 and 1:10. The substrates are put into the HF-solution for about 30 s and dried with the N2-nozzle. When the Si has been ”dipped” long enough the liquid drips down. The so cleaned surface shows hydrophobic characteristics due to a temporary hydrogen-passivation, and inhibits new oxidation for some
Page 1: J O H A N N E S K E P L E R U N I V
Page 4 and 5: ii PREFACE Kurzfassung Eine kinetis
Page 6 and 7: iv PREFACE
Page 8 and 9: vi CONTENTS 2.1.3 Growth-Modes . .
Page 10 and 11: viii CONTENTS B General Physical Da
Page 13 and 14: Chapter 1 Silicon-Germanium Materia
Page 15 and 16: 1.1. STRUCTURAL PROPERTIES 5 Figure
Page 17 and 18: 1.2. VICINAL SI(001) 7 Vicinal subs
Page 19 and 20: 1.3. ELECTRONIC PROPERTIES 9 Monoat
Page 21 and 22: 1.3. ELECTRONIC PROPERTIES 11 Silic
Page 23 and 24: 1.4. SILICON GERMANIUM ALLOYS (SI1
Page 25 and 26: Chapter 2 Molecular Beam Epitaxy (M
Page 27 and 28: 2.1. MBE-GROWTH 17 hit the substrat
Page 29 and 30: 2.1. MBE-GROWTH 19 Figure 2.3: The
Page 31: 2.2. CLEANING PROCEDURE 21 rameter
Page 35 and 36: 2.3. MBE-SYSTEM 25 Figure 2.7: All-
Page 37 and 38: 2.3. MBE-SYSTEM 27 Figure 2.9: Sche
Page 39 and 40: Chapter 3 Methods of Investigation
Page 41 and 42: 3.2. SCANNING ELECTRON MICROSCOPY (
Page 43 and 44: 3.3. ATOMIC FORCE MICROSCOPY (AFM)
Page 51: Part II Main Research 41
Page 54 and 55: 44 CHAPTER 4. SELF-ORGANIZED GROWTH
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72 CHAPTER 5. SELF-ORGANIZED GROWTH
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86 CHAPTER 6. P-MODULATION DOPING A
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100 CHAPTER 6. P-MODULATION DOPING
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Chapter 7 Transient-Enhanced Si Dif
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7.3. EXPERIMENTAL RESULTS 117 > 100
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7.3. EXPERIMENTAL RESULTS 119 Figur
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7.4. DETAILED CHARACTERIZATION AND
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7.4. DETAILED CHARACTERIZATION AND
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Chapter 8 Germanium Source Reconstr
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Figure 8.2: Elevated front-view of
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water lines. Figure 8.4: Photograph
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Figure 8.7: Part 2 of final constru
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Appendix A Calibration and Characte
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A.1. CALIBRATIONS 135 Figure A.1: X
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A.1. CALIBRATIONS 137 Figure A.3: N
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A.2. PHOTOLUMINESCENCE 139 Sample 1
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A.2. PHOTOLUMINESCENCE 141 Figure A
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A.2. PHOTOLUMINESCENCE 143 Figure A
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Appendix B General Physical Data B.
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Bibliography [1] Herbert Lichtenber
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BIBLIOGRAPHY 149 [42] M. B. Prince,
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BIBLIOGRAPHY 151 [85] J. Zhu, K. Br
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BIBLIOGRAPHY 153 [130] C. S. Peng,
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BIBLIOGRAPHY 155 [174] G. Medeiros-
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BIBLIOGRAPHY 157 [214] G. Bastard,
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Postface Curriculum Vitae ⋄ ∗ 1
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POSTFACE 161 � D. Gruber, D. Pach
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POSTFACE 163 Abbreviations AFM Atom
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