Graduation Semester and Year

2014

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Department

Electrical Engineering

First Advisor

Robert Magnusson

Abstract

This dissertation addresses the guided-mode resonance (GMR) effect and its applications. In particular, this study presents theoretical analysis and corresponding experiments on two important GMR devices that can be broadly described as GMR-enabled thin-film solar cells and flat-top reflectors.The GMR-induced enhanced absorption of input light is observed and quantified in a fabricated nano-patterned amorphous silicon (a-Si) thin-film. Compared to a reference homogeneous thin-film of a-Si, approximately 50% integrated absorbance enhancement is achieved in the patterned structure. This result motivates the application of these resonance effects in thin-film solar cells where enhanced solar absorbance is a crucial requirement. Light trapping in thin-film solar cells through the GMR effect is theoretically explained and experimentally demonstrated. Nano-patterned solar cells with 300-nm periods in one-dimensional gratings are designed, fabricated, and characterized. Compared to a planar reference solar cell, around 35% integrated absorption enhancement is observed over the 450-750-nm wavelength range. This light-management method results in enhanced short-circuit current density of 14.8 mA/cm2, which is a ~40% improvement over planar solar cells. The experimental demonstration proves the potential of simple and well-designed guided-mode resonant features in thin-film solar cells. In order to complement the research on GMR thin-film solar cells, a single-step, low-cost fabrication method for generating resonant nano-grating patterns on poly-methyl-methacrylate (PMMA; plexiglas) substrates using thermal nano-imprint lithography is reported. The imprinted structures of both one and two dimensional nano-grating patterns with 300 nm period are fabricated. Thin films of indium-tin-oxide and silicon are deposited over patterned substrates and the absorbance of the films is measured. Around 25% and 45% integrated optical absorbance enhancement is observed over the 450-nm to 900-nm wavelength range in one- and two-dimensional patterned samples, respectively. In addition, two types of GMR flat-top reflectors have been designed, analyzed, fabricated and experimentally demonstrated. The first one is GMR broadband reflector in the spectral domain whereas the second is a Rayleigh reflector in the angular domain. The designed broadband reflector exhibits more than 99% reflectance over a spectral width of 380 nm ranging from 1440 to 1820 nm wavelength. Experimental reflectance greater than 90% is achieved over a ~360-nm bandwidth. The reported reflector bandwidth exceeds comparable published results for two-part periodic structures working in transverse electric polarization. In the Rayleigh reflector, the interaction of GMR and Rayleigh anomaly creates an extraordinary photonic response and results in a flat-top angularly delimited optical filter. The physical process of the rapid energy exchange between the reflected zero-order wave and a propagating substrate wave across a small angular change is investigated with numerical computations. An experimental proof of the Rayleigh reflector concept is presented. The combined GMR-Rayleigh anomaly effect holds the potential to portend a new research area of novel photonic devices with interesting and useful attributes.

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

Download

Share

COinS