For Group IV materials, including silicon, germanium, and their alloys, although they are most widely used in the electronics industry, the development of photonic devices is hindered by indirect band gaps and large lattice mismatches. Thus, any heterostructures involving Si and Ge (4.17% lattice mismatch) are subject to plastic relaxation by dislocation formation in the heterolayers. These defects make many devices impossible and at minimum degrade the performance of those that are possible. Fabrication using elastic strain engineering in Si/SiGe nanomembranes (NMs) is an approach that is showing promise to overcome this limitation. A key advantage of such NM substrates over conventional bulk substrates is that they are relaxed elastically and therefore free of dislocations that occur in the conventional fabrication of SiGe substrates, which are transferred to the epilayers and roughen film interfaces. In this thesis, I use the strain engineering of NMs or NM stacks to fabricate substrates for the epitaxial growth of many repeating units of Si/SiGe heterostructure, known as a 'superlattice', by the elastic strain sharing of a few periods of the repeating unit of Si/SiGe heterolayers or a Si/SiGe/Si tri-layer structure. In both cases, the process begins with the epitaxial growth of Si/SiGe heterolayers on silicon-on-insulator (SOI), where each layer thickness is designed to stay below its kinetic critical thickness for the formation of dislocations. The heterostructure NMs are then released by etching of the SiO2 sacrificial layer in hydrofluoric acid. The resulting freestanding NMs are elastically relaxed by the sharing of strain between the heterolayers. The NMs can be bonded in-place to their host substrate or transferred to another host substrate for the subsequent growth of many periods of superlattice film. The magnitude of strain sharing in these freestanding NMs is influenced by their layer thicknesses and layer compositions. As illustrated in this dissertation, strain-engineering of such NMs can provide the enabling basis for improved Group IV optoelectronic devices.

Strain in crystalline materials alters the atomic symmetry, thereby changing materials properties. Controlling the strain allows tunability of these new properties. Elastic strain engineering in crystalline nanomembranes (NMs) provides ways to induce and relax strain in thin sheets of single-crystalline materials without exposing the material to the formation of extended defects. I use strain engineering in NMs in two ways: (1) elastic strain sharing between multiple layers using the crystalline symmetry of the layers to induce unique strain distributions, and (2) complete elastic relaxation of single-crystalline alloy NMs. In both cases, NM strain engineering methods enable the introduction of unique strain profiles or strain relaxation in ways not compatible with conventional bulk processing, where strain destroys the long-range crystallinity. Elastically strain-shared NMs are fabricated by releasing multi-layer thin film heterostructures from the original host substrate. If one layer of the original heterostructure contains strain, the strain will share between the layers of the freestanding NM. The extent of strain sharing will depend on the relative thicknesses, the ratio of the elastic moduli between the materials, and elastic symmetry of the layers. I calculate strain distributions in flat NMs between layers with 2-fold and 4-fold elastic symmetry. I verify my calculations with experimental proof of two examples: (1) strain sharing between biaxially isotropic layers, Si/SiGe/Si(001), and (2) strain sharing between biaxially anisotropic layers, Si/SiGe/Si(110). Strain engineering in NMs is also used to relax strain elastically in thin materials that are difficult to fabricate with conventional bulk crystal growth techniques. Thin films of SiGe grow uniformly and elastically strained on Si substrates. I release the SiGe layer from the Si growth template with NM fabrication processes and allow the SiGe allow to relax elastically to the appropriate bulk lattice constant. I confirm the high structural quality and strain uniformity of these new materials, and demonstrate their use as substrates for technologically relevant epitaxial films by growing strained Si layers and thick, lattice-matched SiGe alloy layers on them. I compare the structural quality of epitaxial films grown on SiGe NMs to those grown on plastically relaxed SiGe substrates.

Advanced semiconductor technology is depending on innovation and less on "classical" scaling. SiGe, Ge, and Related Compounds has become a key component in the arsenal in improving semiconductor performance. This symposium discusses the technology to form these materials, process them, FET devices incorporating them, Surfaces and Interfaces, Optoelectronic devices, and HBT devices.

"With excellent geometrical flexibility and versatility applicable to various functional materials, self-rolling of strain engineered nanomembranes promises unprecedented possibilities for creating complicated three-dimensional (3D) geometries through programmable shape transformations and attracted enormous scientific interests. It perfectly combines top-down and bottom-up methods, enabling diverse technological applications ranging from nano-elecromechanical/micro-electromechanical systems (NEMS/MEMS) and actuators/sensors, to microrobotics and biotechnology. Challenges remains as understanding of the mechanisms underlying the self-rolling process remains inadequate, which makes it difficult to control geometries of the resultant nanostructures and integrate state-of-the-art functionality required by those applications, thus rendering predictive design strategies of nanostructures from self-rolling not viable. Therefore, aiming to have a deeper and more precise understanding the self-rolling behaviors of strain engineered nanomembranes towards accurately designing complex 3D structures, the present thesis systematically investigated various key aspects, including anisotropic mismatch strain, misfit dislocations, predefined surface patterns, and compositional inhomogeneity affecting the self-rolling process of strain engineered nanomembrane. Combing continuum modeling, numerical and atomistic simulations, the underlying mechanics and physics controlling the self-rolling process were systematically investigated, and predictive mechanics models were developed to provide a generic theoretical framework to guide the design of rolled-up nanostructures.The thesis is manuscript-based, including the investigation of dependence of self-rolling behaviors of nanomembranes on anisotropic mismatch strain (Chapter 4), surface patterning induced curvature variation and rolling direction selection of self-rollup configurations (Chapter 5), misfit dislocation induced mismatch strain relaxation effect (Chapter 6), and effect of compositional inhomogeneity on self-rolling of nanomembranes (Chapter 7). The results of the thesis provide new mechanistic insights towards understanding self-rolling of strain engineered nanomembranes, providing critical guidance for the design and optimization of novel 3D nanomembrane structures." --

An authoritative and comprehensive guide to the devices and applications of Terahertz technology Terahertz (THz) technology relates to applications that span in frequency from a few hundred GHz to more than 1000 GHz. Fundamentals of Terahertz Devices and Applications offers a comprehensive review of the devices and applications of Terahertz technology. With contributions from a range of experts on the topic, this book contains in a single volume an inclusive review of THz devices for signal generation, detection and treatment. Fundamentals of Terahertz Devices and Applications offers an exploration and addresses key categories and aspects of Terahertz Technology such as: sources, detectors, transmission, electronic considerations and applications, optical (photonic) considerations and applications. Worked examplesbased on the contributors extensive experience highlight the chapter material presented. The text is designed for use by novices and professionals who want a better understanding of device operation and use, and is suitable for instructional purposes This important book: Offers the most relevant up-to-date research information and insight into the future developments in the technology Addresses a wide-range of categories and aspects of Terahertz technology Includes material to support courses on Terahertz Technology and more Contains illustrative worked examples Written for researchers, students, and professional engineers, Fundamentals of Terahertz Devices and Applications offers an in-depth exploration of the topic that is designed for both novices and professionals and can be adopted for instructional purposes.