Maximum a posteriori estimation of activation energies that control silicon self-diffusion

a b s t r a c t Self-diffusion in crystalline silicon is controlled by a network of elementary steps whose activation energies are important to know in a variety of applications in microelectronic fabrication. The present work employs maximum a posteriori (MAP) estimation to improve existing values for these activation energies, based on self-diffusion data collected at different values of the loss rates for interstitial atoms to the surface. Parameter sensitivity analysis shows that for high surface loss fluxes, the energy for exchange between an interstitial and the lattice plays the leading role in determining the shape of diffusion profiles. At low surface loss fluxes, the dissociation energy of large-atom clusters plays a more important role. Subsequent MAP analysis provides significantly improved values for these parameters

A multiscale systems approach to microelectronic processes

Abstract This paper describes applications of molecular simulation to microelectronics processes and the subsequent development of techniques for multiscale simulation and multiscale systems engineering. The progression of the applications of simulation in the semiconductor industry from macroscopic to molecular to multiscale is reviewed. Multiscale systems are presented as an approach that incorporates molecular and multiscale simulation to design processes that control events at the molecular scale while simultaneously optimizing all length scales from the molecular to the macroscopic. It is discussed how design and control problems in microelectronics and nanotechnology, including the targeted design of processes and products at the molecular scale, can be addressed using the multiscale systems tools. This provides a framework for addressing the "grand challenge" of nanotechnology: how to move nanoscale science and technology from art to an engineering discipline

Charged Semiconductor Defects: Structure, Thermodynamics and Diffusion

The technologically useful properties of a solid often depend upon the types and concentrations of the defects it contains. Not surprisingly, defects in semiconductors have been studied for many years, in many cases with a view towards controlling their behavior through various forms of "defect engineering." For example, in the bulk, charging significantly affects the total concentration of defects that are available to mediate phenomena such as solid-state diffusion. Surface defects play an important role in mediating surface mass transport during high temperature processing steps such as epitaxial film deposition, diffusional smoothing in reflow, and nanostructure formation in memory device fabrication. Charged Semiconductor Defects details the current state of knowledge regarding the properties of the ionized defects that can affect the behavior of advanced transistors, photo-active devices, catalysts, and sensors. Features: Group IV, III-V, and oxide semiconductors; Intrinsic and extrinsic defects; and, Point defects, as well as defect pairs, complexes and clusters. A crucial reference for materials scientists, surface scientists, electrical engineers, and solid-state physicists looking to approach the topic of defect charging from an integrated chemical engineering perspective. Researchers and industrial practitioners alike will find its content invaluable for device and process optimization

Surface-Based Control of Oxygen Interstitial Injection into ZnO via Submonolayer Sulfur Adsorption

Semiconductor surfaces offer efficient pathways for injecting native point defects into the underlying bulk. Adsorption of a suitably chosen foreign element serves to modulate the injection rate, even at small percentages of a monolayer. Through self-diffusion experiments using isotopic exchange with labeled oxygen, the present work demonstrates such behavior in the case of sulfur adsorption on <i>c</i>-axis Zn-terminated ZnO(0001), wherein the clean surface injects with exceptional efficiency. The experiments provide strong evidence that the injection sites comprise only a small fraction of the total surface atom density and that sulfur adsorption merely blocks those sites. Comparison with related systems shows this simple mechanism is surprisingly uncommon

Control of Methylene Blue Photo-Oxidation Rate over Polycrystalline Anatase TiO2 Thin Films via Carrier Concentration

Reaction rates on photocatalytic surfaces would often benefit greatly if minority photocar-riers could be driven more efficiently to the surface through the manipulation of electric fields within the semiconductor. Such field-induced manipulation of photocurrent is commonplace in conventional optoe-lectronics, but translation to photochemistry and photoelectrochemistry has lagged. The present work demonstrates quantitatively that manipulation of the spatial extent of band bending via background carrier concentration can increase photoreaction rates by a factor of five or more in the case of methylene blue photodegradation over thin-film polycrystalline anatase TiO2. A quantitative photocurrent model fits closely to experimental rate data with no adjustable parameters.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Control of Photoactivity over Polycrystalline Anatase TiO 2 Thin Films via Surface Potential

The utility of thin-film TiO2 for photocatalysis would be greatly improved if the spatial variation of the electronic band edges near the surface could be engineered a priori to control the current of photogenerated minority carriers. The present work demonstrates such a concept. In particular, remote oxygen plasma treatment of polycrystalline anatase TiO2 with specified majority carrier concentration is employed in the test case of methylene blue photodegradation. The photoreaction rate varies by up to 35% in concert with a 0.4 eV change in built-in surface potential measured by photoelectron spectroscopy. The correlation between these changes agrees quantitatively with a photodiode–photocurrent model. The plasma treatment affects concentration of charged native defects within the first few atomic layers of the surface, most likely by lowering the concentration of oxygen vacancies within surface crystallites. In tandem, the position in the deep bulk is controlled via engineering the defect concentration at grain boundaries, thus illustrating the coordinated use of multiple defect engineering practices in polycrystalline material to accomplish quantitative manipulation of band bending and corresponding photocurrent.ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio