拓樸絕緣體硒化鉍薄膜的電壓可調控電漿子波導

Abstract

現今高速運算與資料傳輸需求不斷提升，光電元件漸漸取代傳統電子傳輸鏈路，成為次世代通訊與計算系統的核心技術。為突破繞射極限對光場侷限的限制，電漿子波導（plasmonic waveguide）因具備亞波長尺度的光場侷限能力而備受關注，尤其在折射率調變應用中展現高度靈敏性與整合潛力。我的研究提出一種可電壓調控的電漿子光調變器，結合拓樸絕緣體硒化鉍（Bi2Se3）薄膜與金屬–介電質電漿子波導結構，實現於可見光波段中的寬頻光調變。 本研究首先採用氣相沉積技術於藍寶石基板上合成高品質硒化鉍薄膜，並透過聚甲基丙烯酸甲酯輔助轉移技術，將其成功轉移至已製備的電漿子波導上，避免直接成長時材料品質下降的問題。透過施加外加偏壓調控界面載子注入行為，進而改變硒化鉍的折射率，並影響金的自由電子濃度與其複數介電常數，實現對表面電漿極化子（surface plasmon polariton）傳輸特性的主動調變。實驗顯示，在施加十伏特偏壓、波導長度為一百微米的情況下，消光比（extinction ratio）可高達百分之四十九點一，相較未覆蓋硒化鉍的情況（百分之二十八點九）有顯著提升，並觀察到高達四十八點三奈米的波長紅移現象。 此調變效應可歸因於能帶填充效應（Burstein–Moss 效應），透過金與硒化鉍界面所產生的電子注入與能帶彎曲效應。此外，硒化鉍薄膜於可見光區的高吸收性與可調光學性質，相較於石墨烯與其他傳統二維材料，在低電壓操作下表現出更佳的調變效率。 本研究證實，拓樸絕緣體硒化鉍薄膜能提升電漿子波導的光調變性能，並提供一種具可擴展性的製程方法，應用於未來低功耗、可重構的奈米光子元件，例如高速光開關、可調濾波器與多波長通訊模組。

With the growing demand for high-speed computing and data transmission, optoelectronic devices are gradually replacing traditional electronic interconnects, becoming a core technology for next-generation communication and computing systems. To overcome the diffraction limit that restricts light confinement, plasmonic waveguides have attracted significant attention due to their ability to confine optical fields at subwavelength scales. This makes them highly sensitive and integrable for refractive index modulation. In this work, we propose a voltage-tunable plasmonic optical modulator by integrating topological insulator bismuth selenide (Bi₂Se₃) thin films with a metal–dielectric plasmonic waveguide, achieving broadband optical modulation in the visible spectrum. High-quality Bi₂Se₃ films were synthesized on sapphire substrates via vapor-phase deposition and subsequently transferred to the prepared waveguides using a polymer-assisted (PMMA) method, avoiding the degradation associated with direct growth. By applying an external bias, carrier injection at the Bi₂Se₃–metal interface was modulated, altering the refractive index of Bi₂Se₃ and the free carrier density of the metal, thereby enabling active control of surface plasmon polariton (SPP) propagation. Under a 10 V bias and a 100 μm waveguide length, the device achieved an extinction ratio of 49.1%, significantly higher than the 28.9% observed without Bi₂Se₃, along with a redshift in peak wavelength of up to 48.3 nm. This modulation is attributed to the Burstein–Moss effect, interfacial electron transfer, and band bending at the Bi₂Se₃–gold interface. The strong intrinsic absorption of Bi₂Se₃ in the visible range and its tunable optical properties enable low-voltage operation and superior modulation performance compared to traditional two-dimensional materials such as graphene. This study demonstrates that topological insulator Bi₂Se₃ thin films can enhance the modulation efficiency of plasmonic waveguides. The proposed fabrication strategy offers scalability and is promising for future low-power and reconfigurable nanophotonic devices such as high-speed optical switches, tunable filters, and multi-wavelength communication modules.