Author: Andrew Philip Lange Publisher: ISBN: 9781369615760 Category : Languages : en Pages :
Book Description
This dissertation examines the growth of aluminum nitride (AlN) on (111) silicon by metalorganic chemical vapor deposition. AlN is commonly used as a buffer layer for the growth of gallium nitride on silicon templates. This makes the development of growth protocols for high quality, smooth AlN films on silicon critical to improving the performance and reliability of III-nitride on silicon devices such as light emitting diodes and high power transistors. The optimal nucleation conditions for AlN on silicon have been heavily disputed. Some crystal growers expose the substrate to aluminum prior to AlN deposition, which has been shown to improve crystal quality and decrease surface roughness of both AlN buffer layers and overgrown gallium nitride. However, others adopt an ammonia-first approach, in which the substrate is nitrided prior to AlN deposition. Both can be effective depending on the growth conditions, which has resulted in considerable controversy regarding how aluminum, nitrogen, and silicon interact during these initial "predoses" and how the resulting morphology influences subsequent AlN and gallium nitride growth. The structure and morphology of aluminum predose layers deposited directly on (111) silicon at ~970 °C both with and without subsequent ammonia exposure were studied using electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Three morphological features were identified -- trenches, islands, and patches. When the predose layer was not exposed to ammonia, a roughening of the substrate was observed, similar to what occurs when gallium reacts with silicon. This gave rise to aluminum rich surface trenches, which suggests that silicon is dissolved by liquid aluminum and the resulting aluminum-silicon liquid solution evaporates. When the predose layer was exposed to ammonia, faceted patches were observed with small islands near their edges. The islands were composed of both zinc-blende and wurtzite AlN polytypes, while the patches consisted of diamond cubic silicon with dilute concentrations of aluminum. A model was proposed to explain these features in which the liquid aluminum-silicon surface layer is converted into AlN and silicon upon nitridation. Low temperature and high temperature AlN growth was examined after varied aluminum predoses using electron microscopy and atomic force microscopy with the aim of explaining anomalous AlN-silicon interface structures observed by others. AlN formed small, three-dimensional islands when grown directly on the substrate at ~970 °C with no predose. When the substrate was first exposed to a predose at ~970 °C, AlN nucleated on both island and patch features causing them to grow laterally and eventually coalesce. The morphologies of films grown with and without predoses were nearly identical after coalescence. This suggests that growth at this temperature is kinetically limited and does not depend on the nucleation surface. At high temperatures (~1060 °C), enhanced lateral growth on patch features formed during the predose was observed. The AlN-silicon interface was found to be predominantly amorphous when no predose was used, consistent with previous reports. The interface was structurally abrupt when aluminum was deposited prior to growth, but contained an additional phase consistent with the zinc-blende islands observed in predose layers. It was proposed that the amorphous SiN[subscript x] interfacial layer formed between nucleation sites when no predose was used as the substrate was exposed to an ammonia ambient prior to lateral growth of the nuclei. When the substrate was first exposed to a predose, aluminum rich silicon patches covered the surface. The presence of aluminum in the patches may limit the reaction between silicon and nitrogen during the early stages of growth. Dislocations in buffer layers grown both with and without aluminum predoses were studied using weak beam dark field transmission electron microscopy. A mosaic microstructure was observed which consisted of clustered dislocations along subgrain boundaries. Many of these subgrains were not bounded by dislocations on all sides, which suggests they did not form by the coalescence of misaligned islands. It was proposed they formed instead by the clustering of dislocations due to attractive and repulsive interactions. Dislocation densities were lower in films grown with a predose, which resulted in the formation of fewer subgrains. It was also found that buffers grown with a predose had a smoother surface. The surface of buffer layers grown without a predose contained small pits along the edges of surface terraces. The separation and geometry of these terraces was consistent with the subgrain structure, indicating surface step bunching may occur around subgrains where dislocation densities are high. Consistent with III-nitride growth on alternative substrates, a-type threading dislocations with line directions normal to the basal plane were found to terminate within highly defective, low temperature nucleation layers. C-type threading dislocations were found to terminate near the AlN-Si interface. It was suggested that the former originate from the climb of basal plane dislocations which form through the dissociation of Shockley partials or the coalescence of I1 type stacking faults. It was suggested that the latter nucleate from surface steps on the substrate. The observed improvement in crystal quality of buffer layers grown with a predose may be due to dislocation annihilation events, rather than the nucleation of fewer threading dislocations. This is corroborated by the presence of voids in the substrate when the buffer was grown with a predose, which indicates that point defects diffuse across the abrupt interface during growth. The presence of amorphous interfaces in films grown without an aluminum predose may inhibit the diffusion of point defects and thereby deter dislocation climb. If this mechanism is active as evidence in this dissertation suggests, an appropriate objective of any nucleation process for AlN buffer layers on silicon may be to improve the structural coherence of the interface.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphology of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).
Author: Mohamed Henini Publisher: Newnes ISBN: 0123918596 Category : Technology & Engineering Languages : en Pages : 745
Book Description
This multi-contributor handbook discusses Molecular Beam Epitaxy (MBE), an epitaxial deposition technique which involves laying down layers of materials with atomic thicknesses on to substrates. It summarizes MBE research and application in epitaxial growth with close discussion and a 'how to' on processing molecular or atomic beams that occur on a surface of a heated crystalline substrate in a vacuum.MBE has expanded in importance over the past thirty years (in terms of unique authors, papers and conferences) from a pure research domain into commercial applications (prototype device structures and more at the advanced research stage). MBE is important because it enables new device phenomena and facilitates the production of multiple layered structures with extremely fine dimensional and compositional control. The techniques can be deployed wherever precise thin-film devices with enhanced and unique properties for computing, optics or photonics are required. This book covers the advances made by MBE both in research and mass production of electronic and optoelectronic devices. It includes new semiconductor materials, new device structures which are commercially available, and many more which are at the advanced research stage. - Condenses fundamental science of MBE into a modern reference, speeding up literature review - Discusses new materials, novel applications and new device structures, grounding current commercial applications with modern understanding in industry and research - Coverage of MBE as mass production epitaxial technology enhances processing efficiency and throughput for semiconductor industry and nanostructured semiconductor materials research community
Author: Krzysztof Iniewski Publisher: CRC Press ISBN: 1439836213 Category : Medical Languages : en Pages : 760
Book Description
As rapid technological developments occur in electronics, photonics, mechanics, chemistry, and biology, the demand for portable, lightweight integrated microsystems is relentless. These devices are getting exponentially smaller, increasingly used in everything from video games, hearing aids, and pacemakers to more intricate biomedical engineering and military applications. Edited by Kris Iniewski, a revolutionary in the field of advanced semiconductor materials, Integrated Microsystems: Electronics, Photonics, and Biotechnology focuses on techniques for optimized design and fabrication of these intelligent miniaturized devices and systems. Composed of contributions from experts in academia and industry around the world, this reference covers processes compatible with CMOS integrated circuits, which combine computation, communications, sensing, and actuation capabilities. Light on math and physics, with a greater emphasis on microsystem design and configuration and electrical engineering, this book is organized in three sections—Microelectronics and Biosystems, Photonics and Imaging, and Biotechnology and MEMs. It addresses key topics, including physical and chemical sensing, imaging, smart actuation, and data fusion and management. Using tables, figures, and equations to help illustrate concepts, contributors examine and explain the potential of emerging applications for areas including biology, nanotechnology, micro-electromechanical systems (MEMS), microfluidics, and photonics.
Author: Reet Chaudhuri Publisher: Springer Nature ISBN: 3031171993 Category : Technology & Engineering Languages : en Pages : 266
Book Description
This thesis outlines the principles, device physics, and technological applications of electronics based on the ultra-wide bandgap semiconductor aluminum nitride. It discusses the basic principles of electrostatics and transport properties of polarization-induced two-dimensional electron and hole channels in semiconductor heterostructures based on aluminum nitride. It explains the discovery of high-density two-dimensional hole gases in undoped heterojunctions, and shows how these high conductivity n- and p-type channels are used for high performance nFETs and pFETs, along with wide bandgap RF, mm-wave, and CMOS applications. The thesis goes on to discuss how the several material advantages of aluminum nitride, such as its high thermal conductivity and piezoelectric coefficient, enable not just high performance of transistors, but also monolithic integration of passive elements such as high frequency filters, enabling a new form factor for integrated RF electronics.
Author: Rositsa Gergova Publisher: ISBN: Category : Afterglow (Physics) Languages : en Pages : 298
Book Description
"The work presented in this thesis investigates the growth and properties of group III- nitride semiconductors that were grown using the Migration Enhanced Afterglow Epitaxy (MEAglow) method. This work was to enhance the understanding of the MEAglow growth process towards the improvement of quality of the layers grown using this technique. The MEAglow technique applies the migration enhanced epitaxy method in a low pressure plasma-based CVD reactor, which has a potential of producing high quality epitaxial group III-nitride layers at relatively low growth temperatures on large deposition areas. The low temperature pulse growth in metal-rich regime, comprising the MME method was employed under growth pressures between 500 mTorr and 3000 mTorr. As the MME method up to this point has been used only for MBE systems, study of the impact of the growth pressure on the materials properties was necessary. In this work the pressure dependence was mapped to an existing surface phase diagram for MBE systems by calculating the number of nitrogen gas phase collisions and the metalorganic bombardment rate, for the specific to the prototype reactor parameters, to a first approximation. This was done in order to achieve an intermediate regime free of metal droplets for growth in metal-rich regime. High quality epitaxial InN layers were accomplished on extremely thin and smooth Ga2O3 buffer layers. These results indicate a potential for the application of Ga2O3 buffers in InN growth. The MEAglow InN layers were further optimized for growth on commercially available GaN buffer layers and excellent two-dimensional growth was achieved for layers grown under metal-rich conditions at 512 °C. Post-growth annealing studies were carried out for InN layers grown at temperatures below 400 °C to study the limiting processes of the removal of excess nitrogen, believed to be a dominant defect in InN films grown in plasma-based systems at very low temperatures. Variations in GaN stoichiometry under certain growth conditions and the effect of similar growth conditions on MEAglow grown InGaN were also examined. The growth of MEAglow InGaN samples on sapphire substrates was optimized to reduce the indium surface segregation and phase separation of the material."-- from abstract.
Author: Andrew Philip Lange
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Author: Mohamed Henini
Author: Krzysztof Iniewski
Author: Claudio Ronald Miskys
Author: Reet Chaudhuri
Author: Rositsa Gergova