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

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30 CHAPTER 3. METHODS OF INVESTIGATION 3.1 Transmission Electron Microscopy (TEM) Optical microscopes are limited in image resolution due to the long wavelength of visible light. Historically, this has been the reason for the introduction of electrons into microscopy. After de Broglie’s famous equation (Eq. 3.1), in which particle momentum p and its wavelength λ are related via Planks’s constant h, λ = h p (de Broglie) → λ[nm] ∼ 1.22 � E[eV ] (3.1) and from a simple transformation, high energy 200 keV-electrons (accelerated by a corre- sponding voltage of 200 kV) have a wavelength λ of about 2.5 pm (0.0025 nm), which is sub- stantially smaller than atomic diameters. This diffraction limit of resolution is out of reach, mainly due to electron lenses. These are the crucial and limiting point in electron microscopy since electromagnetic lenses are by far not perfect. Compared to glass lenses that can be pro- duced with perfect quality the best electromagnetic lenses would correspond to ”the bottom of a Coke bottle as magnifying glass” (cite Williams and Carter [73]). Typical values for the practical resolution of a TEM are 0.15–0.3 nm and therefore the maximum useful magnification in the best high-resolution TEM is about 10 6 (resolution of eye approximately 0.1 mm). For thick samples these limit of resolution cannot be obtained due to the increased energy spread ∆E resulting in chromatic aberration. The mean free path for inelastic scattering depends on the electron energy, and therefore with higher acceleration voltages good high resolution can even be achieved with relative thick samples (50 nm) [73, 75, 76]. Sample preparation has to be performed carefully and is probably the most important step in order to obtain good high-resolution images. It demands great skill to prepare thin electron- transparent (→ 50–100 nm!) specimen over a wide area. Ideally, the volume considered for TEM-analysis should be free of defects and artifacts originated by the time consuming preparation. In order to image the corrugation of buried interfaces (see Ch. 6), or the wire profile of the pro- cessed Si-samples (see Ch. 7), cross-sectional specimen have to be prepared. The preparation cycle for cross-sectional (Si-)samples is outlined in Ref. [1]. The specimen in this work were investigated with a JEOL-2011 FasTEM (HR type) transmission electron microscope [77] with an acceleration voltage of 200 kV using a LaB6-cathode. For this TEM facility a point image resolution of 0.23 nm is specified; the magnification can be chosen from 2000 to 1.5 million. Images are either recorded with a conventional photo-plate camera, or, nowadays, mainly with a Gatan CCD-camera (1 megapixel).
3.2. SCANNING ELECTRON MICROSCOPY (SEM) 31 3.2 Scanning Electron Microscopy (SEM) Scanning electron microscopy can be used to study and analyze (mainly the surface of) bulk specimen. The information is derived from the interaction between the probe electrons and the specimen. The focussed electron beam is deflected by scan coils and the probe is scanned across the specimen in a raster mode. Synchronous to this scanning process, the signals generated by the probe beam interaction with the specimen are detected. The recorded in- tensity modulation gives the contrast in SEM images. The scanning process can be applied to generate a magnified image of the sample. The newly commissioned LEO (ZEISS) SUPRA� 35 FESEM provides access to nanoscale resolution images without an elaborate sample preparation (specified resolution: 1.7 nm @ 15 kV). It is well-suited to characterize the surface after critical processing steps, or to investigate etched profiles in cross-sectional view (Sec. 7.2). An SEM combines the possibili- ties to give a fast overview over the whole specimen area and to zoom-in for a more-detailed inspection of the surface morphology. It provides a large magnification range of typically 20x–500 000x). For more facts the reader is referred to the diploma-thesis (Ref. [1]) and the PhD-thesis written by T. Berer [78]. 3.3 Atomic Force Microscopy (AFM) Atomic Force Microscopy (AFM) is a further development on the basis of scanning probe microscopy (SPM) implemented in the mid 1980’s. The AFM is an imaging tool with a vast dynamic range, spanning the realms of optical and electron microscopes, and is operated as a surface profiler with unprecedented 3D-resolution [74]. In atomic force microscopy the surface of a sample is scanned with a sharp tip that is several micrometers long and has a smallest diameter of typically 10 nm. It is located on the free end of a cantilever (∼ 100–200 µm in length). Forces between the sample and the tip cause the cantilever to bend or deflect. As the tip scans across the surface, these deflections are measured with a detector and allow a computer to generate topographic maps [74]. The force most commonly associated with cantilever deflection in atomic force microscopy is the interatomic van der Waals force. The dependence of this van der Waals force upon the distance between the tip and the sample surface is depicted in Fig. 3.1 [74]. Three distance regimes are labelled in Fig. 3.1: 1) Contact regime, 2) Non-contact regime (NC), and, in between, 3) Intermittent-contact regime (IC). In the so-called contact mode the tip is held
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 and 32: 2.2. CLEANING PROCEDURE 21 rameter
Page 33 and 34: 2.2. CLEANING PROCEDURE 23 H2SO4 :
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: Chapter 3 Methods of Investigation
Page 43 and 44: 3.3. ATOMIC FORCE MICROSCOPY (AFM)
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80 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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