No description available.

This thesis deals with the main aspects in chemical vapordeposition (CVD) of silicon (Si) and silicon-germanium (Si1-xGex) films for high-speed bipolar transistors.In situdoping of polycrystalline silicon (poly-Si)using phosphine (PH3) and disilane (Si2H6) in a low-pressure CVD reactor was investigated toestablish a poly-Si emitter fabrication process. The growthkinetics and P incorporation was studied for amorphous Si filmgrowth. Hydrogen (H) incorporated in the as-deposited films wasrelated to growth kinetics and the energy for H2desorption was extracted. Film properties such asresistivity, mobility, carrier concentration and grain growthwere studied after crystallization using either furnaceannealing or rapid thermal annealing (RTA). In order tointegrate an epitaxial base, non-selective epitaxial growth(NSEG) of Si and SiGe in a lamp-heated single-waferreduced-pressure CVD reactor was examined. The growth kineticsfor Si epitaxy and poly-Si deposition showed a differentdependence on the deposition conditions i.e. temperature andpressure. The growth rate difference was mainly due to growthkinetics rather than wafer surface emissivity effects. However,it was observed that the growth rate for Si epitaxy and poly-Sideposition was varying during growth and the time-dependencewas attributed to wafer surface emissivity variations. A modelto describe the emissivity effects was established, taking intoconsideration kinetics and the reactor heating mechanisms suchas heat absorption, emission andconduction. Growth ratevariations in opening of different sizes (local loading) andfor different oxide surface coverage (global loading) wereinvestigated. No local loading effects were observed, whileglobal loading effects were attributed to chemical as well astemperature effects. Finally, misfit dislocations formed in theSiGe epitaxy during NSEG were found to originate from theinterface between the epitaxial and polycrystalline regions.The dislocations tended to propagate across the activearea. <b>Keywords:</b>chemical vapor deposition (CVD), bipolarjunction transistor (BJT), heterojunction bipolar transistor(HBT), silicon-germanium (SiGe), epitaxy, poly-Si emitter,in situdoping, non-selective epitaxy (NSEG), loadingeffect, emissivity effect

No description available.

<p>This thesis deals with the main aspects in chemical vapordeposition (CVD) of silicon (Si) and silicon-germanium (Si_1-xGe_x) films for high-speed bipolar transistors.<i>In situ</i>doping of polycrystalline silicon (poly-Si)using phosphine (PH₃) and disilane (Si₂H₆) in a low-pressure CVD reactor was investigated toestablish a poly-Si emitter fabrication process. The growthkinetics and P incorporation was studied for amorphous Si filmgrowth. Hydrogen (H) incorporated in the as-deposited films wasrelated to growth kinetics and the energy for H₂desorption was extracted. Film properties such asresistivity, mobility, carrier concentration and grain growthwere studied after crystallization using either furnaceannealing or rapid thermal annealing (RTA). In order tointegrate an epitaxial base, non-selective epitaxial growth(NSEG) of Si and SiGe in a lamp-heated single-waferreduced-pressure CVD reactor was examined. The growth kineticsfor Si epitaxy and poly-Si deposition showed a differentdependence on the deposition conditions i.e. temperature andpressure. The growth rate difference was mainly due to growthkinetics rather than wafer surface emissivity effects. However,it was observed that the growth rate for Si epitaxy and poly-Sideposition was varying during growth and the time-dependencewas attributed to wafer surface emissivity variations. A modelto describe the emissivity effects was established, taking intoconsideration kinetics and the reactor heating mechanisms suchas heat absorption, emission andconduction. Growth ratevariations in opening of different sizes (local loading) andfor different oxide surface coverage (global loading) wereinvestigated. No local loading effects were observed, whileglobal loading effects were attributed to chemical as well astemperature effects. Finally, misfit dislocations formed in theSiGe epitaxy during NSEG were found to originate from theinterface between the epitaxial and polycrystalline regions.The dislocations tended to propagate across the activearea.</p><p><b>Keywords:</b>chemical vapor deposition (CVD), bipolarjunction transistor (BJT), heterojunction bipolar transistor(HBT), silicon-germanium (SiGe), epitaxy, poly-Si emitter,<i>in situ</i>doping, non-selective epitaxy (NSEG), loadingeffect, emissivity effect</p>

SiGe is a significant enabling technology for therealization of integrated circuits used in high performanceoptical networks and radio frequency applications. In order tocontinue to fulfill the demands for these applications, newmaterials and device structures are needed. This thesis focuseson new materials and their integration into heterojunctionbipolar transistor (HBT) structures as well as using devicesimulations to optimize and better understand the deviceoperation. Specifically, a SiGeC HBT platform was designed,fabricated, and electrically characterized. The platformfeatures a non-selectively grown epitaxial SiGeC base,in situdoped polysilicon emitter, nickel silicide,LOCOS isolation, and a minimum emitter width of 0.4 μm.Alternately, a selective epitaxy growth in an oxide window wasused to form the collector and isolation regions. Thetransistors exhibited cutoff frequency (fT) and maximum frequency of oscillation (fMAX) of 40-80 GHz and 15-45 GHz, respectively.Lateral design rules allowed the investigation of behavior suchas transient enhanced diffusion, leakage current, and theinfluence of parasitics such as base resistance and CBC. The formation of nickel silicide on polysiliconSiGe and SiGeC films was also investigated. The formation ofthe low resistivity monosilicide phase was shown to occur athigher temperatures on SiGeC than on SiGe. The stability of themonosilicide was also shown to improve for SiGeC. Nickelsilicide was then integrated into a SiGeC HBT featuring aselectively grown collector. A novel, fully silicided extrinsicbase contact was demonstrated along with the simultaneousformation of NiSi on thein situdoped polysilicon emitter. High-resolution x-ray diffraction (HRXRD) was used toinvestigate the growth and stability of SiGeC base layers forHBT integration. HRXRD proved to be an effective, fast,non-destructive tool for monitoring carbon out-diffusion due tothe dopant activation anneal for different temperatures as wellas for inline process monitoring of epitaxial growth of SiGeClayers. The stability of the SiGe layer with 0.2-0.4 at% carbonwhen subjected to dopant activation anneals ranging from1020-1100&amp;#176C was analyzed by reciprocal lattice mapping.It was found that as the substitutional carbon increases theformation of boron clusters due to diffusion is suppressed, buta higher density of carbon clusters is formed. Device simulations were performed to optimize the DC and HFperformance of an advanced SiGeC HBT structure with low baseresistance and small dimension emitter widths. The selectivelyimplanted collector (SIC) was studied using a design ofexperiments (DOE) method. For small dimensions the lateralimplantation straggle has a significant influence on the SICprofile (width). A significant influence of the SIC width onthe DC gain was observed. The optimized structure showedbalanced fT/fMAXvalues of 200+ GHz. Finally, SOI BJT transistorswith deep trench isolation were fabricated in a 0.25μmBiCMOS process and self-heating effects were characterized andcompared to transistors on bulk silicon featuring deep trenchand shallow trench isolation. Device simulations based on SEMcross-sections and SIMS data were performed and the resultscompared to the fabricated transistors. Key words:Silicon-Germanium(SiGe), SiGeC,heterojunction bipolar transistor(HBT), nickel silicide,selectively implanted collector(SIC), device simulation, SiGeClayer stability, high resolution x-ray diffraction(HRXRD),silicon-on-insulator(SOI), self-heating.

No description available.

No description available.

<p>SiGe is a significant enabling technology for therealization of integrated circuits used in high performanceoptical networks and radio frequency applications. In order tocontinue to fulfill the demands for these applications, newmaterials and device structures are needed. This thesis focuseson new materials and their integration into heterojunctionbipolar transistor (HBT) structures as well as using devicesimulations to optimize and better understand the deviceoperation. Specifically, a SiGeC HBT platform was designed,fabricated, and electrically characterized. The platformfeatures a non-selectively grown epitaxial SiGeC base,<i>in situ</i>doped polysilicon emitter, nickel silicide,LOCOS isolation, and a minimum emitter width of 0.4 μm.Alternately, a selective epitaxy growth in an oxide window wasused to form the collector and isolation regions. Thetransistors exhibited cutoff frequency (f_T) and maximum frequency of oscillation (f_MAX) of 40-80 GHz and 15-45 GHz, respectively.Lateral design rules allowed the investigation of behavior suchas transient enhanced diffusion, leakage current, and theinfluence of parasitics such as base resistance and C_BC. The formation of nickel silicide on polysiliconSiGe and SiGeC films was also investigated. The formation ofthe low resistivity monosilicide phase was shown to occur athigher temperatures on SiGeC than on SiGe. The stability of themonosilicide was also shown to improve for SiGeC. Nickelsilicide was then integrated into a SiGeC HBT featuring aselectively grown collector. A novel, fully silicided extrinsicbase contact was demonstrated along with the simultaneousformation of NiSi on the<i>in situ</i>doped polysilicon emitter.</p><p>High-resolution x-ray diffraction (HRXRD) was used toinvestigate the growth and stability of SiGeC base layers forHBT integration. HRXRD proved to be an effective, fast,non-destructive tool for monitoring carbon out-diffusion due tothe dopant activation anneal for different temperatures as wellas for inline process monitoring of epitaxial growth of SiGeClayers. The stability of the SiGe layer with 0.2-0.4 at% carbonwhen subjected to dopant activation anneals ranging from1020-1100&#176C was analyzed by reciprocal lattice mapping.It was found that as the substitutional carbon increases theformation of boron clusters due to diffusion is suppressed, buta higher density of carbon clusters is formed.</p><p>Device simulations were performed to optimize the DC and HFperformance of an advanced SiGeC HBT structure with low baseresistance and small dimension emitter widths. The selectivelyimplanted collector (SIC) was studied using a design ofexperiments (DOE) method. For small dimensions the lateralimplantation straggle has a significant influence on the SICprofile (width). A significant influence of the SIC width onthe DC gain was observed. The optimized structure showedbalanced f_T/f_MAXvalues of 200+ GHz. Finally, SOI BJT transistorswith deep trench isolation were fabricated in a 0.25μmBiCMOS process and self-heating effects were characterized andcompared to transistors on bulk silicon featuring deep trenchand shallow trench isolation. Device simulations based on SEMcross-sections and SIMS data were performed and the resultscompared to the fabricated transistors.</p><p><b>Key words:</b>Silicon-Germanium(SiGe), SiGeC,heterojunction bipolar transistor(HBT), nickel silicide,selectively implanted collector(SIC), device simulation, SiGeClayer stability, high resolution x-ray diffraction(HRXRD),silicon-on-insulator(SOI), self-heating.</p>

The research conducted in this dissertation studies the issues regarding the improvement of phase noise performance in a BiCMOS Silicon Germanium (SiGe) cross-coupled differential-pair voltage controlled oscillator (VCO) in a narrowband application as a result of a tail-current shaping technique. With this technique, low-frequency noise components are reduced by increasing the signal amplitude without consuming additional power, and its effect on overall phase noise performance is evaluated. The research investigates effects of the tail-current as a main contributor to phase noise, and also other effects that may influence the phase noise performance like inductor geometry and placement, transistor sizing, and the gain of the oscillator. The hypothesis is verified through design in a standard 0.35 μm BiCMOS process supplied by Austriamicrosystems (AMS). Several VCOs are fabricated on-chip to serve for a comparison and verify that the employment of tail-current shaping does improve phase noise performance. The results are then compared with mathematical models and simulated results, to confirm the hypothesis. Simulation results provided a 3.3 dBc/Hz improvement from -105.3 dBc/Hz to -108.6 dBc/Hz at a 1 MHz offset frequency from the 5 GHz carrier when employing tail-current shaping. The relatively small increase in VCO phase noise performance translates in higher modulation accuracy when used in a transceiver, therefore this increase can be regarded as significant. Parametric analysis provided an additional 1.8 dBc/Hz performance enhancement in phase noise that can be investigated in future works. The power consumption of the simulated VCO is around 6 mW and 4.1 mW for the measured prototype. The circuitry occupies 2.1 mm2 of die area. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

Spatial confinement of electrons and their interactions as well as confinement of the spin dimensionality often yield drastic changes of the electronic and magnetic properties of solids. Novel quantum transport and optical phenomena, involving electronic spin degrees of freedom in semiconductor heterostructures, as well as a rich variety of exotic quantum ground states and magnetic excitations in complex transition metal oxides that arise upon such confinements, belong therefore to topical problems of contemporary condensed matter physics. In this work electron spin systems in reduced dimensions are studied with Electron Spin Resonance (ESR) spectroscopy, a method which can provide important information on the energy spectrum of the spin states, spin dynamics, and magnetic correlations. The studied systems include quasi onedimensional spin chain materials based on transition metals Cu and Ni. Another class of materials are semiconductor heterostructures made of Si and Ge. Part I deals with the theoretical background of ESR and the description of the experimental ESR setups used which have been optimized for the purposes of the present work. In particular, the development and implementation of axial and transverse cylindrical resonant cavities for high-field highfrequency ESR experiments is discussed. The high quality factors of these cavities allow for sensitive measurements on μm-sized samples. They are used for the investigations on the spin-chain materials. The implementation and characterization of a setup for electrical detected magnetic resonance is presented. In Part II ESR studies and complementary results of other experimental techniques on two spin chain materials are presented. The Cu-based material Linarite is investigated in the paramagnetic regime above T > 2.8 K. This natural crystal constitutes a highly frustrated spin 1/2 Heisenberg chain with ferromagnetic nearest-neighbor and antiferromagnetic next-nearestneighbor interactions. The ESR data reveals that the significant magnetic anisotropy is due to anisotropy of the g-factor. Quantitative analysis of the critical broadening of the linewidth suggest appreciable interchain and interlayer spin correlations well above the ordering temperature. The Ni-based system is an organic-anorganic hybrid material where the Ni2+ ions possessing the integer spin S = 1 are magnetically coupled along one spatial direction. Indeed, the ESR study reveals an isotropic spin-1 Heisenberg chain in this system which unlike the Cu half integer spin-1/2 chain is expected to possess a qualitatively different non-magnetic singlet ground state separated from an excited magnetic state by a so-called Haldane gap. Surprisingly, in contrast to the expected Haldane behavior a competition between a magnetically ordered ground state and a potentially gapped state is revealed. In Part III investigations on SiGe/Si quantum dot structures are presented. The ESR investigations reveal narrowlines close to the free electron g-factor associated with electrons on the quantum dots. Their dephasing and relaxation times are determined. Manipulations with sub-bandgap light allow to change the relative population between the observed states. On the basis of extensive characterizations, strain, electronic structure and confined states on the Si-based structures are modeled with the program nextnano3. A qualitative model, explaining the energy spectrum of the spin states is proposed.:Abstract i Contents iii List of Figures vi List of Tables viii 1 Preface 1 I Background and Experimental 5 2 Principles of ESR 7 2.1 The Resonance Phenomenon . . . . . . . . . . . . . . . . . . . 7 2.2 ESR Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 The g -factor . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 Relaxation Times . . . . . . . . . . . . . . . . . . . . . . 12 2.2.3 Lineshape Properties . . . . . . . . . . . . . . . . . . . . 13 2.3 Effective Spin Hamiltonian . . . . . . . . . . . . . . . . . . . . . 15 2.4 Spin-Orbit Coupling . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.5 d-electrons in a Crystal Field . . . . . . . . . . . . . . . . . . . . 17 2.6 Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.6.1 Dipolar Coupling . . . . . . . . . . . . . . . . . . . . . . 23 2.6.2 Exchange Interaction . . . . . . . . . . . . . . . . . . . . 23 2.6.3 Superexchange . . . . . . . . . . . . . . . . . . . . . . . 24 2.6.4 Symmetric Anisotropic Exchange . . . . . . . . . . . . 25 2.6.5 Antisymmetric Anisotropic Exchange . . . . . . . . . . 25 2.6.6 Hyperfine Interaction . . . . . . . . . . . . . . . . . . . 26 3 Experimental 27 3.1 Setup for Experiments at 10GHz . . . . . . . . . . . . . . . . . 27 3.2 Implementation of an EDMR Setup . . . . . . . . . . . . . . . . 29 3.2.1 Basic Characterization . . . . . . . . . . . . . . . . . . . 31 3.3 High Frequency Setup . . . . . . . . . . . . . . . . . . . . . . . . 31 3.3.1 MillimeterWave Vector Network Analyzer . . . . . . . 33 3.3.2 Waveguides and Cryostats . . . . . . . . . . . . . . . . . 34 3.4 Development of the Resonant Cavity Setup . . . . . . . . . . . 35 3.4.1 Mode Propagation . . . . . . . . . . . . . . . . . . . . . 38 3.4.2 Resonant CavityModes . . . . . . . . . . . . . . . . . . 40 3.4.3 Resonant Cavity Design . . . . . . . . . . . . . . . . . . 41 3.4.4 Resonant Cavity Sample Stick . . . . . . . . . . . . . . . 45 3.4.5 Experimental Characterization . . . . . . . . . . . . . . 47 3.4.6 Performing an ESR Experiment . . . . . . . . . . . . . . 53 II Quasi One-Dimensional Spin-Chains 57 4 Motivation 59 5 Quasi One-Dimensional Systems 61 5.1 Magnetic Order and Excitations . . . . . . . . . . . . . . . . . . 63 5.2 Competing Interactions . . . . . . . . . . . . . . . . . . . . . . . 64 5.3 Haldane Spin Chain . . . . . . . . . . . . . . . . . . . . . . . . . 66 6 Linarite 69 6.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 6.2 Magnetization and ESR . . . . . . . . . . . . . . . . . . . . . . . 71 6.3 NMR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.4 Summary and Conclusion . . . . . . . . . . . . . . . . . . . . . 81 6.5 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 7 The Ni-hybrid NiCl3C6H5CH2CH2NH3 83 7.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 7.2 Susceptibility andMagnetization . . . . . . . . . . . . . . . . . 85 7.3 ESR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 7.4 Further Investigations . . . . . . . . . . . . . . . . . . . . . . . . 95 7.5 Summary and Conclusion . . . . . . . . . . . . . . . . . . . . . 96 8 Summary 99 III SiGe Nanostructures 101 9 Motivation 103 10 SiGe Semiconductor Nanostructures 107 10.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 10.1.1 Silicon and Germanium . . . . . . . . . . . . . . . . . . 107 10.1.2 Epitaxial Growth of SiGe Heterostructures . . . . . . . 109 10.1.3 Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 10.1.4 Band Deformation . . . . . . . . . . . . . . . . . . . . . 112 10.2 Sample Structure and Characterization . . . . . . . . . . . . . 114 11 Modelling of SiGe/Si Heterostructures 119 11.1 Program Structure . . . . . . . . . . . . . . . . . . . . . . . . . . 120 11.2 Implementation of Si/Ge System . . . . . . . . . . . . . . . . . 121 11.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 11.3.1 Single Quantum Dot . . . . . . . . . . . . . . . . . . . . 123 11.3.2 Multiple Quantum Dots . . . . . . . . . . . . . . . . . . 127 11.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 11.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 12 ESR Experiments on Si/SiGe Quantum Dots 135 12.1 ESR on Si Structures . . . . . . . . . . . . . . . . . . . . . . . . . 135 12.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . 137 12.2.1 Samples grown at 600◦C . . . . . . . . . . . . . . . . . . 138 12.2.2 Samples grown at 700◦C . . . . . . . . . . . . . . . . . . 139 12.2.3 T1-Relaxation Time . . . . . . . . . . . . . . . . . . . . . 143 12.2.4 Effect of Illumination . . . . . . . . . . . . . . . . . . . . 145 12.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 12.3.1 Quantum Dots . . . . . . . . . . . . . . . . . . . . . . . 149 12.3.2 Assignment of ESR Lines . . . . . . . . . . . . . . . . . . 150 12.3.3 Relaxation Times . . . . . . . . . . . . . . . . . . . . . . 153 12.3.4 Donors in Heterostructures . . . . . . . . . . . . . . . . 153 12.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 13 Summary and Outlook 157 Bibliography 163 Acknowledgements 176