Characterizations of Surface Plasmon Behaviors in InGaN/GaN Quantum-well Light Emitters with Metallic Structures and in Metal Nanoparticles Formed by Laser Irradiation
Date Issued
2009
Date
2009
Author(s)
Chen, Cheng-Yen
Abstract
In this dissertation, we first study the metallic-structure dependent surface plasmon (SP) coupling behaviors with a blue-emitting InGaN/GaN quantum well (QW), which is 10 nm away from the metallic structures. The SP-QW coupling behaviors in the areas of semiconductor surface coated with Ag thin film and Ag nanoparticles are compared. It is found that both the suppression of photoluminescence (PL) intensity and the reduction of time-resolved PL (TRPL) decay time strongly depend on the metallic morphology. A phenomenological rate-equation model of carrier relaxation in the SP-QW coupling process is built to fit the TRPL decay profiles for calibrating the reasonable decay time constants of carrier and SP.ext, we analyze the contribution of the screening of the quantum-confined Stark effect (QCSE) to the emission enhancement behavior in the process of SP coupling with an InGaN/GaN QW, which is 20 nm away from an Ag thin film that supports the SP. From the measurements of excitation power-dependent PL and TRPL spectroscopy, and the fitting to the TRPL data based on the modified rate-equation model, it is found that when the excitation level is high, the QCSE screening effect not only contributes significantly to the emission enhancement, but also increases the SP coupling rate because of the blue shift of emission spectrum caused by the screening effect. Therefore, the emission strength from SP radiation, relative to that from QW radiative recombination, increases with the excited carrier density. Also, a saturation behavior of SP-QW coupling is observed from the fitting procedure.esides, we report the characterizations of the SP features on a 1-D Ag-grating structure through the SP coupling with an InGaN/GaN dual-QW structure closely below the metal grating. We build an angle-resolved PL measurement system to observe the SP features. Polarized photon output is observed because only the momentum matching condition of the SP mode propagating in the direction perpendicular to the grating grooves can be reached through the diffraction of the fabricated grating. Hence, the SP radiation efficiency is significantly enhanced only in this polarization. We also calibrate the group velocity of the observed SP mode from the measured dispersion curves. With the Ag-grating structure used in the experiment, the SP dispersion properties can be manipulated by changing the dielectric material surrounding the grating structure.inally, we demonstrate the fabrications of sphere-like Au nanoparticles (NPs) of similar shapes and alignments on sapphire, GaN, and SiO2 substrates through the irradiation of a few pulses of 266-nm laser onto Au thin films deposited on the substrates. The top-view diameter, contact angle on substrate, surface population density, and surface coverage percentage of the NPs can be controlled by the Au thin film thickness, laser energy density, substrate choice, and the gas or liquid, in which the Au thin film is immersed during laser irradiation. Due to the fixed orientation of NPs, optical transmission measurements show clear in-plane and out-of-plane localized surface plasmon resonance (LSPR) features, including the air resonance feature dictated by the gas or liquid immersing the NPs during transmission measurement, the in-plane substrate resonance feature controlled by the substrate material and the contact angle, and the out-of-plane resonance feature, which is strongly influenced also by the substrate material and the contact angle. Numerical simulations based on the finite-element method using the experimental parameters show highly consistent LSPR spectral positions and their variation trends. From the simulation results, one can also observe the relative importance between NP absorption and scattering in contributing to the extinction. This simple laser-irradiation method for fabricating fixed-orientation sphere-like Au NPs of no aggregation and of strong adhesion to the substrate is useful for developing polarization-sensitive LSPR bio-sensing.
Subjects
表面電漿；氮化銦鎵；奈米顆粒；雷射照射；光柵；色散
Type
thesis
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