Applications of Vapor Deposition in Microelectronics and Dye-Sensitized Solar Cells

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Applications of Vapor Deposition in Microelectronics and Dye-Sensitized Solar Cells

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Title: Applications of Vapor Deposition in Microelectronics and Dye-Sensitized Solar Cells
Author: Wang, Xinwei
Citation: Wang, Xinwei. 2012. Applications of Vapor Deposition in Microelectronics and Dye-Sensitized Solar Cells. Doctoral dissertation, Harvard University.
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Abstract: Over the past decades, vapor deposition of thin films has gained wide interest in both industry and academia, and a variety of its applications have been demonstrated. As one of the most promising vapor deposition techniques, atomic layer deposition (ALD) and its applications in microelectronics and dye-sensitized solar cells are extensively investigated in this dissertation. ALD has many distinct features including low temperature processing, self-limiting growth, and precise control of film composition and thickness. Thus, ALD is considered to be suitable for conformal coating of 3D nanostructures, such as nanoporous structures, high aspect-ratio trench or hole structures, and so forth. Additionally, pulsed chemical vapor deposition (CVD) and its applications in microelectronics are explored in this dissertation. Ruthenium (Ru) is a promising electrode material for next generation microelectronic devices. The ALD and pulsed CVD processes discussed in Chapter 2 provide several approaches to produce smooth, conformal, pin-hole free Ru metal thin films. High-quality Ru films can be made under either oxidizing ambient or reducing ambient, which provides more flexibility for applications in microelectronics. Conductive ruthenium dioxide \((RuO_2)\) is also considered as a promising microelectrode material. Chapter 3 demonstrates a pulsed CVD process of depositing pure, smooth \((RuO_2)\) films with reasonably low resistivity. Chapter 3 also demonstrates that \((RuO_2)\) can be epitaxially grown on rutile \(TiO_2(011)\) with a high-quality coherent heteroepitaxy structure. III-V MOSFET is now a very active area of growing interest to researchers and engineers in electronic industry and academia. Applications of ALD WN and high-k oxide materials for GaAs and GaN based devices are investigated in Chapters 4 and 5. Taking advantage of the conformal-coating feature of ALD, a stack of gate dielectric and metal gate can be coated uniformly around suspended nanowire structures, which is crucial for well-behaved gate-all-around MOSFETs. III-V MOSFETs also generally lack a suitable dielectric layer that has low interface trap density \((D_{it})\). Epitaxial ALD high-k dielectric lanthanum yttrium oxide, grown on GaAs(111)A, is found to have a fairly low \((D_{it})\), and therefore, the electrical properties are dramatically improved with its inclusion. This finding is very insightful for the applications of next generation III-V MOSFETs. In addition, a few ALD processes of candidate dielectric materials for GaN based devices are discussed. Dye-sensitized solar cells have great potential to compete with conventional p-n junction solar cells due to their relatively low cost. However, their efficiency is limited by the ease with which electrons collected by the nanoparticle framework can recombine with ions in solution. As discussed in Chapter 6, by depositing insulating and transparent \(SiO_2\) selectively onto the open areas of nanoparticulate \(TiO_2\) surface, while avoiding any deposition of \(SiO_2\) over or under the organic dye molecules, the solar cell efficiency can be significantly improved.
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