結合金屬光柵於鍺/二氧化鈦Tamm電漿態結構之多波長窄頻熱發射器研究

Abstract

本論文旨在利用上層金屬光柵結合雙層的鍺/二氧化鈦分散式布拉格反射器之混合堆疊結構來研究中紅外波段(3~9μm)的多波長熱輻射發射器。首先，使用光學薄膜厚度公式設計工作在波長為4 μm的分散式布拉格反射器結構，接著利用模擬軟體設計金屬光柵於雙層的鍺/二氧化鈦分散式布拉格反射器上，分別分析在入射光極化方向平行於與垂直於光柵周期下的共振模態與頻譜特徵。最後，使用黃光製程來完成樣品的製作，並利用傅里葉轉換紅外光譜量測比對實驗與模擬結果是否吻合。在入射光極化方向平行於光柵周期時，複合式Tamm plasmon結構同時激發出三種共振模態，包含hybridized Tamm plasmon電磁態、間隙模態與侷域在中間鍺層的波導模態。而在TM極化下，則激發出hybridized Tamm plasmon電磁態、侷域在頂層鍺層的波導模態、侷域在底層鍺層的波導模態與侷域表面電漿子共振。藉由模擬計算，我們系統性分析這些共振模態的光學特性，包含光柵結構與上層鍺膜厚對這些共振模態的頻譜響應、改變入射光角度的影響等，並製作出一系列具不同金屬光柵間距與上層鍺厚度的樣品來驗證理論結果，最後成功設計出具結構可調性、低角度相依性之三波長窄頻的熱輻射發射器，未來期望應用於提高分子感測應用之靈敏度與準確性。

We aim to study mid-infrared (3~9μm) thermal emitters based on a hybrid structure combining a gold grating structure on top of a double-paired germanium/titanium dioxide (Ge/TiO2) distributed Bragg reflector (DBR). First, we used the optical thinfilm thickness formula to calculate the thickness of the distributed Bragg reflector working at the wavelength of 4 μm. Then, the simulation software was implemented to design the grating structure on top of the double-layer Ge/TiO2 DBR and analyze different resonant modes and spectral profiles under transverse electric (TE) and transverse magnetic (TM) polarizations. Finally, the samples were fabricated by a standard photolithography process and the Fourier-transform infrared spectroscopy was utilized to characterize the optical properties of samples. Under TE polarization, three resonance modes are simultaneously excited, including hybridized Tamm plasmon mode, the gap mode, and the middle-guided mode (MG mode). Under TM polarization, four resonant modes are simultaneously excited, including hybridized Tamm plasmon mode, the top-guided mode (TG mode), the bottom-guided mode (BG mode), and the localized surface plasmon (LSPs). We systematically analyzed the optical properties of these resonant modes via simulations, including the effects of grating structure, the thickness of top Ge cavity, and the oblique incident angle on the resonant wavelengths. Then, a serious of samples with different gap sizes and top Ge thicknesses were fabricated to validate the theoretical results. Finally, triple-narrowband, small angular dependent thermal emitters with additional degree of freedom in adjusting the spectral position of each mode were realized, which is promising for enhancing the accuracy in discrimination of molecular fingerprint.