Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

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Titanium dioxide (TiO2) thin films have a long history in silicon photovoltaics (PV) as antireflection (AR) coatings due to their excellent optical properties and low deposition cost. This work explores several novel areas where TiO2 thin films could be use to enhance silicon (Si) solar cell performance while reducing device fabrication costs. Amorphous, anatase and rutile TiO2 thin films are deposited using ultrasonic spraydeposition (USD) and chemical vapour deposition (CVD) systems, both designed and constructed by the author. Initial experiments confirmed that no degradation in the bulk minority carrier lifetime (????bulk) occurred during high-temperature processing, although the stability of the USD-deposited TiO2 films was dependent on the furnace ambient. A major disadvantage of TiO2 AR coatings is that they afford little surface passivation. In this work, a novel method of achieving excellent surface passivation on TiO2-coated silicon wafers is presented. This involved growing a 6 nm-thick SiO2 layer at the TiO2:Si interface by oxidising the wafer after TiO2 film deposition. The increase in surface passivation afforded by the interfacial SiO2 layer results in a decrease in the emitter dark saturation current density (J0e) by nearly two orders of magnitude to 4.7 ??? 7.7 ??~ 10???14 A/cm2. This demonstrates the compatibility of the TiO2/SiO2 stack with high-efficiency solar cells designs. By varying the film deposition and annealing conditions, TiO2 refractive indices in the range of 1.726 ??? 2.633 (at ???? = 600 nm) could be achieved. Subsequently, a double-layer antireflection (DLAR) coating was designed comprised of low and high TiO2 refractive index material. The best experimental weighted average reflectance (Rw) achieved was 6.5% on a planar silicon wafer in air. TiO2 DLAR coatings are ideally suited to multicrystalline silicon (mc-Si) wafers, which do not respond well to chemical texturing. Modelling performed for a glass and ethyl vinyl acetate (EVA) encapsulated buried-contact solar cell indicated that a TiO2 DLAR coating afforded a 7% increase in the short circuit current density, when compared to a standard, commercially-deposited TiO2 single-layer AR coating. Finally, it is demonstrated that chemical reactions with phosphorus prevent TiO2 from acting as a successful phosphorus diffusion barrier or dopant source. The applicability of TiO2 thin films to various silicon solar cell structures is discussed.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 221-230).

This thesis examines the excimer-laser-induced melting of ELA-prepared silicon films using in situ transient reflectance and transmission analysis. The results clearly show that these polycrystalline films, which consist of columnar grains in contact with SiO₂, can melt in a largely and remarkably 2-D manner. Based on the presently and previously obtained experimental results, as well as considering the thermal, thermodynamic, and kinetic aspects of the melting-transition-relevant details, we suggest a model that consists of grain-boundary-initiated melting, followed by lateral melting proceeding into the transiently superheated interior of the grains. Additional experiments are performed which demonstrate how this 2-D melting behavior at least stems intrinsically from the presence in the material of melt-prone grain boundaries and superheating-permitting Si/SiO₂ interfaces. Next, the phase and temperature evolutions of the irradiated films are investigated using a numerical simulation program, which incorporates key material, thermodynamic, and kinetic parameters. We find that the center portion of the grains during (partial) melting (1) corresponds to, especially at the SiO₂-passivated surface, the hottest regions of the films during rapid heating, and (2) remains entirely solid throughout the thickness of the film, as the maximum temperature sustained in these unmelted solids remains well below the superheating limit of silicon at the Si/SiO₂ interface. Lastly, we discuss, and substantiate with results obtained from numerical simulations, the role that the manifested dimensionality of melting plays in dictating the efficiency with which the ELA crystallization technique can generate microstructurally uniform polycrystalline materials. The current discovery regarding the 2-D nature of melting should be recognized and appreciated as a critical process-enabling element for ELA, as the scenario permits microstructure evolution of the grains to take place in an effective manner.

Xue Kun. / "July 2005." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese.

Diode lasers have many advantages such as small size, high efficiency and small angular dispersion of the collimated beam. However they also have some problems like lack of frequency stability. They can not be tuned in wavelength. An external cavity can solve these problems and decrease the laser linewidth. To obtain a tunable, narrow linewidth light source, antireflection coatings were applied to commercial diode lasers which were then tested in an external cavity. Laser characteristics, such as threshold current, spectral behavior, I-V-curves, tuning range, and bandwidth were measured for the original diode laser and then compared to the measurements in an external cavity with and without antireflection (AR) coatings. The tuning range approximately doubled after AR coating. The modal stability was found to be better by a factor of 7 in the external cavity. The power amplification through the external cavity was as high as 50. It was also attempted to process laser diodes from material fabricated at OSU, however the resulting diodes showed a high series resistance and were not usable for this project. Additional work needs to be done in this area. The result of this work is a stable external cavity diode laser tunable over an 18 nm bandwidth which can be used as a tunable source in many applications. / Graduation date: 1995