Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisors: Sanjay K. Banerjee and Gyeong S. Hwang. Vita. Includes bibliographical references.

Silicon based materials, including silicon oxides and silicon oxynitrides, have found use in a number of areas in photonics including waveguides, antireflection and highly reflective coatings for laser facets, and detectors. For effective use of these materials in photonics it is necessary to characterize their optical properties as a function of their composition and structure. Since these characteristics are often dependent on the method used to deposit the films it is necessary to also determine the effect of deposition type and conditions on the film's properties. Recently, silicon based materials have been seen to display luminescence due to quantum confinement effects when nanocrystals are formed. This opens up the possibility of a silicon based emitter, something that has not had previous success due to the indirect bandgap of bulk silicon. The development of a silicon based emitter in turn would open up the possibility for monolithically integrated photonic circuits that could take advantage of CMOS processing technology. This thesis presents the results of research into the characterization of amorphous silicon and silicon oxide thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition. Optical properties of the films have been determined through the use of ellipsometry and correlated with the results from compositional analysis, done using Rutherford backscattering and elastic recoil detection, and bonding structure analysis, done using Fourier transform infrared spectroscopy. Nanocrystals were formed within the films by subjecting them to post-deposition thermal annealing, which induces a phase separation in silicon rich silicon oxide films. The effects of different annealing conditions on composition, structure and optical properties have also been analyzed. Finally, photoluminescence experiments were conducted on the films and correlated with the results from other characterization techniques. / Thesis / Master of Applied Science (MASc)

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.

In this thesis, silicon oxide thin films fabricated on silicon substrates by reactive radio frequency (rf) magnetron sputtering and supercritical CO2 (SCCO2) treatment at room temperature were investigated. The electrical properties including I-V and C-V of the films prepared at different processing conditions were discussed. Using the Transmission Electron Microscope (TEM), the thickness of silicon oxide thin films were measured. The results suggested that the film quality can be significantly improved by the SCCO2 treatment after reactive sputtering. The leakage current of the films at an electrical field of 1 MV/cm is 1¡Ñ10-8A/cm2 with a hysteresis voltage of 0.01V. The silicon oxide thin films can be used as a barrier layer for Al/SiO2/Si silicon solar cells. The energy conversion efficiency of a single crystal silicon solae cell is 10.2% under AM1.5 (965W/m2) radiation. After rapid thermal annealing(RTA) at 500¢J, the measured short-circuit current, open- circuit voltage, fill factor are 53mA, 0.54V and 0.53, respectively.

In this study, SiO2 and TiO2 films were deposited on GaN, their physical and chemical properties were measured. An Al/SiO2/GaN and Al/TiO2/GaN MOS structures were used for the electrical measurements. To improve the electrical properties, we investigated the characteristics of SiO2 and TiO2 films after annealing in nitrogen, oxygen, and nitrous oxide ambient. The highest dielectric constant of 3.91 and 28.68, and lowest leakage current density of 8.97¡Ñ10-5 A/cm2 at 2 MV/cm and 2¡Ñ10-2 A/cm2 at 1 MV/cm for the N2O-annealed SiO2 film and TiO2 film can be obtained.

Silicon oxynitride (SiON) films for applications of optical waveguide devices deposited using plasma-enhanced chemical vapor deposition were investigated. The SiON films were deposited on 4¡¨ silicon wafers based on the reaction of N2O/SiH4 precursors. The refractive indices of the films were adjusted by varying the partial pressure of SiH4 in the precursors. In addition, films prepared at conventional flow (~1500 sccm) and low flow (~1000 sccm) conditions were compared. We found that the nitrogen content of the films grown at low flow conditions can be significantly reduced resulting in a reduction of absorption around 1500 nm. Therefore SiON films grown at low flow conditions would be more suitable for optical waveguide fabrication. Finally, with the aid of the beam propagation method (BPM) software, a single-mode optical waveguide based on the proposed technology was designed and fabricated. The propagation loss was 0.79dB/cm for TE polarization, and 0.73db/cm for T

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 120-134). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Lehigh University, 2001. / Includes bibliographical references and vita.

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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