Strained Ge And Gesn Band Engineering For Si Photonic Integrated Circuits

The on-chip interconnect bandwidth limitation is becoming an increasingly critical challenge for integrated circuits (ICs) as device scaling continues to push the speed and density of ICs. Silicon photonics has the ability to solve this emerging problem due to its high speed, high bandwidth, low power consumption, and ability to be monolithically integrated on silicon. Most of the key devices for Si photonic ICs have already been demonstrated. However, a practical CMOS compatible coherent light source is still a major challenge. Germanium (Ge) has already been demonstrated to be a promising material for optoelectronic devices, such as photo-detectors and modulators. However, Ge is an indirect band gap semiconductor, which makes Ge-based light sources very inefficient and limits their practical use. Fortunately, the direct [uppercase Gamma] valley of the Ge conduction band is only 0.14 eV higher than the indirect L valley, suggesting that with band-structure engineering, Ge has the potential to become a direct band gap material and an efficient light emitter. In this dissertation, we first discuss our work on highly biaxial tensile strained Ge grown by molecular beam epitaxy (MBE). Relaxed step-graded InGaAs buffer layers, which are prepared with low temperature growth and high temperature annealing, are used to provide a larger lattice constant substrate to produce tensile strain in Ge epitaxial layers. Up to 2.3% in-plane biaxial tensile strained thin Ge epitaxial layers were achieved with smooth surfaces and low threading dislocation density. A strong increase of photoluminescence with highly tensile strained Ge layers at low temperature suggests that a direct band gap semiconductor has been achieved. This dissertation also presents our work on more than 9% Sn incorporation in epitaxial GeSn alloys using a low temperature MBE growth method. This amount of Sn is 10 times greater than the solid-solubility of Sn in crystalline Ge. Material characterization shows good crystalline quality without Sn precipitation or phase segregation. With increasing Sn percentage, direct band gap narrowing is observed by optical transmission measurements. The studies described in this dissertation will help enable efficient germanium based CMOS compatible coherent light sources. Other possible applications of this work are also discussed in the concluding chapter.

The on-chip interconnect bandwidth limitation is becoming an increasingly critical challenge for integrated circuits (ICs) as device scaling continues to push the speed and density of ICs. Silicon photonics has the ability to solve this emerging problem due to its high speed, high bandwidth, low power consumption, and ability to be monolithically integrated on silicon. Most of the key devices for Si photonic ICs have already been demonstrated. However, a practical CMOS compatible coherent light source is still a major challenge. Germanium (Ge) has already been demonstrated to be a promising material for optoelectronic devices, such as photo-detectors and modulators. However, Ge is an indirect band gap semiconductor, which makes Ge-based light sources very inefficient and limits their practical use. Fortunately, the direct [uppercase Gamma] valley of the Ge conduction band is only 0.14 eV higher than the indirect L valley, suggesting that with band-structure engineering, Ge has the potential to become a direct band gap material and an efficient light emitter. In this dissertation, we first discuss our work on highly biaxial tensile strained Ge grown by molecular beam epitaxy (MBE). Relaxed step-graded InGaAs buffer layers, which are prepared with low temperature growth and high temperature annealing, are used to provide a larger lattice constant substrate to produce tensile strain in Ge epitaxial layers. Up to 2.3% in-plane biaxial tensile strained thin Ge epitaxial layers were achieved with smooth surfaces and low threading dislocation density. A strong increase of photoluminescence with highly tensile strained Ge layers at low temperature suggests that a direct band gap semiconductor has been achieved. This dissertation also presents our work on more than 9% Sn incorporation in epitaxial GeSn alloys using a low temperature MBE growth method. This amount of Sn is 10 times greater than the solid-solubility of Sn in crystalline Ge. Material characterization shows good crystalline quality without Sn precipitation or phase segregation. With increasing Sn percentage, direct band gap narrowing is observed by optical transmission measurements. The studies described in this dissertation will help enable efficient germanium based CMOS compatible coherent light sources. Other possible applications of this work are also discussed in the concluding chapter.

This fourth book in the series Silicon Photonics gathers together reviews of recent advances in the field of silicon photonics that go beyond already established and applied concepts in this technology. The field of research and development in silicon photonics has moved beyond improvements of integrated circuits fabricated with complementary metal–oxide–semiconductor (CMOS) technology to applications in engineering, physics, chemistry, materials science, biology, and medicine. The chapters provided in this book by experts in their fields thus cover not only new research into the highly desired goal of light production in Group IV materials, but also new measurement regimes and novel technologies, particularly in information processing and telecommunication. The book is suited for graduate students, established scientists, and research engineers who want to update their knowledge in these new topics.

Silicon photonics technology, which has the DNA of silicon electronics technology, promises to provide a compact photonic integration platform with high integration density, mass-producibility, and excellent cost performance. This technology has been used to develop and to integrate various photonic functions on silicon substrate. Moreover, photonics-electronics convergence based on silicon substrate is now being pursued. Thanks to these features, silicon photonics will have the potential to be a superior technology used in the construction of energy-efficient cost-effective apparatuses for various applications, such as communications, information processing, and sensing. Considering the material characteristics of silicon and difficulties in microfabrication technology, however, silicon by itself is not necessarily an ideal material. For example, silicon is not suitable for light emitting devices because it is an indirect transition material. The resolution and dynamic range of silicon-based interference devices, such as wavelength filters, are significantly limited by fabrication errors in microfabrication processes. For further performance improvement, therefore, various assisting materials, such as indium-phosphide, silicon-nitride, germanium-tin, are now being imported into silicon photonics by using various heterogeneous integration technologies, such as low-temperature film deposition and wafer/die bonding. These assisting materials and heterogeneous integration technologies would also expand the application field of silicon photonics technology. Fortunately, silicon photonics technology has superior flexibility and robustness for heterogeneous integration. Moreover, along with photonic functions, silicon photonics technology has an ability of integration of electronic functions. In other words, we are on the verge of obtaining an ultimate technology that can integrate all photonic and electronic functions on a single Si chip. This e-Book aims at covering recent developments of the silicon photonic platform and novel functionalities with heterogeneous material integrations on this platform.

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.

This book focuses on advances in materials science and device applications of nanostructures composed of Si, Ge, diamond, SiGe and SiCGe. Continuous progress in the development of reproducibly grown quantum dots, wires and wells has produced a new class of functional materials and devices with characteristic dimensions less than 50nm. The broad spectrum of these devices ranges from commercially offered high-mobility transistors using strained Si to exploratory SiGe nanostructures for integrated optical interconnects and THz lasers. This book brings together researchers from chemistry, physics, biology, materials science and engineering to share and discuss both the challenges and progress towards a new generation of Si(SiGe, SiCGe)-based novel functional structures and devices. Topics include: light emission and photonic devices; Ge, SiGe and diamond nanostructures; strains, Si/Ge films and layers and Si nanocrystals.

Representing a further step towards enabling the convergence of computing and communication, this handbook and reference treats germanium electronics and optics on an equal footing. Renowned experts paint the big picture, combining both introductory material and the latest results. The first part of the book introduces readers to the fundamental properties of germanium, such as band offsets, impurities, defects and surface structures, which determine the performance of germanium-based devices in conjunction with conventional silicon technology. The second part covers methods of preparing and processing germanium structures, including chemical and physical vapor deposition, condensation approaches and chemical etching. The third and largest part gives a broad overview of the applications of integrated germanium technology: waveguides, photodetectors, modulators, ring resonators, transistors and, prominently, light-emitting devices. An invaluable one-stop resource for both researchers and developers.