氧化鋅為具有強極性特性的II-VI寬能隙半導體(~3.37 eV)，並且擁有較大的激子束縛能(~60 meV)，能使激子穩定存在於室溫中。氧化鋅的自然結構具有六角形橫截面能形成耳語迴廊共振腔，使光子能被完美的侷限於共振腔中。基於以上兩點優勢，激子與光子會在共振腔中產生強耦合形成激子極化子，其具有半光半物質的特性。
在本論文將單根氧化鋅微米柱作為研究對象，重點研究氧化鋅微米柱在不同溫度下的光譜特性、色散關係、激子極化子雷射、光學增益、縱向聲子(LO聲子)等物理現象。具有內容包括以下二部份:
第一步部分為激子極化子在不同溫度下的色散關係，為了獲得激子極化子的色散關係必須先取得材料的折射率，首先我們使用微光致發光光譜觀察了不同溫度下耳語迴廊共振腔的光學特性，並計算出近能帶的折射率對於溫度的依賴性。將不同溫度的折射率代入羅倫茲色散模型後，可由色散曲線中提取出與激子極化子有關之物理參數(如拉比分裂能量及前置因子)，最後經過分析可得到溫度與拉比分裂能量之間的關係，並透過理論公式得到解釋。
第二部分為氧化鋅微米柱中的LO聲子有助於激子極化激子雷射產生，我們首先在室溫中實現激子極化子雷射並研究其光學特性，當激發密度大於雷射閥值時，我們可以觀察到光強度呈現非線性的增加及半高全寬急遽下降的雷射特性；隨著激發密度持續上升，雷射波峰呈現藍移的趨勢，並透過觀察光學影像證明激子極化子雷射在空間上具有相干性。接著，我們更進一步探討LO聲子如何輔助激子極化子雷射，由於氧化鋅本身為具有極性的半導體材料，LO聲子能量(~72 meV)與激子束縛能之間的能量接近有助於激子與聲子之間的耦合並由穩態光譜中觀察到多個聲子複製品。因此我們觀察不同溫度下LO聲子的演變及雷射行為清楚表明，氧化鋅微米柱系統中LO聲子在光學增益機制中扮演重要角色，其中光學增益分布隨溫度變化受到自由激子的重吸收影響，再吸收是系統內重要的損耗通道。

Zinc oxide (ZnO) is a II-VI wide bandgap semiconductor with strong polar properties and larger exciton binding energy (~60 meV), which enables excitons to exist at room temperature. The natural structure of ZnO has a hexagonal cross-section that can form the whispering-gallery-mode (WGM) microcavities for perfect photons confinement. Thanks to these two benefits, excitons and photons will generate strong microcavity coupling to form exciton-polaritons with the characteristics of half-light and half-matter. This thesis used a single ZnO microrod (ZnO MR) as the research object, the spectrum characteristics, exciton-polariton dispersion relation, exciton-polariton lasing, optical gain, LO phonon, and other physical phenomena of ZnO MR at different temperatures. The content includes the following two parts:
In the first part of the work, we research the dispersion relation of exciton-polaritons at different temperatures. We should first extract the material's refractive index to obtain the exciton-polariton dispersion relation (E-k relation). First, we observed the optical characteristics of the whispering-gallery-modes (WGMs) at different temperatures by micro-photoluminescence (μ-PL) spectroscopy and calculated the near-bandgap refractive index with temperature. After substituting the refractive index at different temperatures into the Lorentz dispersion model, we can extract the physical parameters (such as Rabi splitting energy and pre-factor, etc.) related to the exciton-polariton from the dispersion curve. Finally, the Rabi splitting energy as a function of temperature can be explained from the theoretical equation.
In the second part of the work, we research the LO phonon-assisted exciton-polariton lasing in ZnO MRs. First, we have realized the exciton-polariton laser at room temperature and observed optical characteristics. When the excitation density is above the lasing threshold, we observed the lasing characteristics that the PL intensity shows the non-linear increase and the drastic drop in FWHM. As the excitation density continues to increase, the lasing peak shows the blueshift trend, and the coherence of the exciton-polariton laser is proved by measuring the real space. Next, we further discuss how LO phonon-assisted the exciton-polariton lasing. Since ZnO is a strong polar semiconductor material, the similarities between the LO phonon energy (~72 meV) and exciton binding energy also enhance the exciton-phonon coupling so that the multi phonon replica can be observed from the steady-state spectra. Therefore, we observe the LO phonon and lasing behavior at different temperatures demonstrating that the LO phonon plays a crucial role in the optical gain mechanism. Notably, the reabsorption, which is a significant loss channel, affects the optical gain distribution with temperature.

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