Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 255-278). Also available in electronic version. Access restricted to campus users.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 62-66). Also available in electronic version. Access restricted to campus users.

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

Includes bibliographical references.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

III-V nitride based light-emitting diodes (LEDs) have experienced rapid developments during past decade, proving their potential to substitute conventional incandescent bulbs and fluorescent lamps to fulfil energy-efficient and sustainable lighting needs. Tremendous endeavours have been made to improve the performance of LEDs, most of which focused on enhancing the internal and external quantum efficiencies. However, other optical properties of LEDs remain to be explored for a more flexible way of using LEDs in various applications. Therefore, this thesis proposes two nanostructuring strategies through the use of nanospheres to tailor the optical properties of LEDs. The nanostructured LEDs are demonstrated enable light emission with reduced divergence, or becomes polarized. The monolithic modifications are free of external optics and thus eliminate light loss, meanwhile providing manipulability of optical emission from LEDs. Firstly, close-packed indium-tin-oxide (ITO) micron-lenses with dimension of the order of wavelength have been integrated onto InGaN LEDs aiming at reducing the emission divergence. The sub-micron lens arrays are patterned by nanosphere lithography with silica nanosphere serving as an etch mask on ITO layer, leaving the semiconductor layer damage-free. An enhancement of up to 63.5% on optical output power from the lensed LED has been observed. The LED with 500 nm lenses exhibits a 26.8° reduction in emission divergence (full width at half maximum) compared with the bare LED. Three-dimensional finite-difference time-domain simulations performed for light extraction and emission characteristics is found to be consistent with the observed results. Secondly, polarization behavior of light emitted from InGaN LEDs propagating through a self-assembled polystyrene nanosphere opal film has been studied. Angular-resolved optical transmission of transverse electric (TE) and transverse magnetic (TM) polarized light has been measured. An integrated p/s ratio of 2.16 is observed at a detection angle of 70°, attributed to the suppression of TE mode at particular frequencies by the three-dimensional photonic crystal. Polarization is found to depend strongly on both the photonic bandgap of the opal and the angle of incidence. Theoretical calculations by transfer matrix method yield results consistent with the experimental data. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

It is observed that the power consumption of road lighting is increased with the length of trafficable road in Hong Kong. The energy used in road lighting is increasing, which means that the greenhouse gases (GHGs) emitted from power plant for generating electricity for road lighting is at the same time increasing. To compare the performance of light emitted diode (LED) road lighting with road lighting of other lamp sources, literature review, life cycle assessment (LCA) and technical assessment are adopted to give an overall comparison. This research focuses more on the environmental impacts of road lighting. LCA is adopted in order to give a comprehensive view on the environmental impact of road lighting. A total of 3 different lamp sources are compared: high pressure sodium (HPS) lamp, induction lamp and light emitted diode (LED) lamp. From the model result, it is found that due to the low power consumption and long life time, LED and induction lamp road lighting gives generally less environmental impact than HPS road lighting. As induction lamp has a longer life span than LED, the environmental impact of induction lamp road lighting is found slightly less than that of LED road lighting. Taking account the future development in LED technology, leading to longer life time, higher efficacy and lower production cost, LED road lighting is expected to be a replacement for road lighting in Hong Kong for the future. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Abstract—A dependency of quantum efficiency of nn+pp+ silicon complementary metal–oxide–semiconductor integrated lightemitting devices on the current density through the active device areas is demonstrated. It was observed that an increase in current density from 1 6 10+2 to 2 2 10+4 A cm 2 through the active regions of silicon n+pp+ light-emitting diodes results in an increase in the external quantum efficiency from 1 6 10 7 to 5 8 10 6 (approximately two orders of magnitude). The light intensity correspondingly increase from 10 6 to 10 1 W cm 2 mA (approximately five orders of magnitude). In our study, the highest efficiency device operate in the p-n junction reverse bias avalanche mode and utilize current density increase by means of vertical and lateral electrical field confinement at a wedge-shaped n+ tip placed in a region of lower doping density and opposite highly conductive p+ regions.

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