Experimental and Theoretical study of emission properties of ZnO-based microresonators

• Main Authors: Ngo, Huynh-Buu-Trong, 吳寶仲
• Other Authors: Chang, Yia-Chung
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/dxmj59

博士 === 國立清華大學 === 工程與系統科學系 === 106 === It is known that light at resonance wavelengths would be confined to optical resonators by a sufficient coupling scheme. Such confinement behaviors are unique and alter the interaction of light with matter due to the lifetime extension of confined photons. Among various states of an arbitrary optical resonator, semiconductor resonators have been considerably attractive for their potential to achieve high Q-factor and low lasing threshold. Hence, the investigation of ZnO-based resonators has a very important impact not only on fundamental research but also on numerous applications in different fields. This thesis presented systematically studies on whispering gallery mode (WGM) in ZnO based-micro spherical resonators (MSRs) (including porous ZnO and Au@ZnO MSRs) grown by hydrothermal synthesis. The protocol of synthesized high-quality spherical resonators by single-pot, low-temperature technique is developed. WGM in these resonators is then explored by micro photoluminescence (μ-PL) spectrometer. The thesis also proposes Modified Refractive Index (MRI) and Effective Medium Theory implemented (EMT) schemes to analyze the PL spectra measured from those ZnO MSRs. These schemes are shown that they are useful not only for precisely assigning resonance mode number and type but also for addressing the unneglectable role of resonator’s components. Finally, the emission luminescence spectra of an arbitrary MSR are reconstructed based on Green functional theory. By comparison to experimental PL, we can get a further understanding of optical properties of MSRs such as leaky modes, stimulated modes and their correlation properties which are not able to be clarified by observation of experimental spectrum only. The scientific advancements covered within this thesis, including the build-up of protocol of synthesis MSRs, models to analyzed the WGM from PL spectra and theory to calculating emission spectra of MSRs, are integrated together to perform a consistent picture of how light interacts inside ZnO MSRs and exhibit WGM behaviors. We show that not only geometry but also components of an MSR affect their WGM. Based on this finding, we propose a solution to overcome the obstacles between size and WGM quality, that is to modify the inner structure by reducing the air fraction or adding more emitting sources (such as plasmonic nanoparticles or quantum dots). By utilizing that approach we can reduce the resonator size to the nanoscale, and yet maintain high-quality WGM. The thesis thus plays a vital asset for the future studies of WGM in nanoscale, which is essential for both fundamental studies of principles mode number and advanced studies on potential applications such as nano-lasing or nano-resonator based bio-devices.