| 摘要: | 近年來，隨著高速光通訊技術的蓬勃發展，對於近紅外波段（Near-Infrared, NIR）
之高效光偵測器的需求日益殷切。在該波段中，目前已成熟的技術以InGaAs PIN 光電
二極體與雪崩式光電二極體為主，雖然擁有良好的線性響應和高靈敏度，但其使用III–
V 材料導致成本較高，製程複雜，且與CMOS 元件整合不易等問題日益顯著。
在此背景下，負光導(negative photoconductance) 光偵測器因其製程簡單與材料成
本低廉等優勢，成為近年新穎的研究方向。本研究以光導特性改變之金屬奈米表面浮雕
光柵(surface relief) 行近紅外光偵測器為基礎，以光通訊波段(1303.5 - 1310 nm) 為目標，設計並製作一具備高吸收率與負光導特性之金屬奈米表面浮雕光柵型近紅外光偵測
器，並導入表面電漿共振(surface plasmon resonance）效應與Fabry–Pérot 共振於結構設計中，進一步增強場強，提升效率。最終經由Lumerical FDTD 模擬軟體中的粒子群
聚演算法（particle swarm optimization, PSO）進行數值模擬與參數優化，得到於TM
偏振光入射下，在波長為1308 nm 與1315.5 nm 處達到60.14% 與60.37% 的銀條內部
吸收率。
脈衝響應的部分，以Lumerical FDTD 對金屬光柵內部具有意義的點上對單一以及
連續三脈衝輸入之訊號進行分析，以證明具底層銀之銀光柵最佳化設計之元件對於高速
光通訊的訊號偵測能力，結果顯示其偵測極限約在2 Tbps 附近，足以充分應付目前高
速光通訊之需求並且對之後的發展展現巨大的潛力。
實際製作出具底層銀之銀光柵最佳化設計之元件S1106D4 並以顯微鏡反射式反
射率量測系統搭配放大倍率10 倍、NA 值為0.3 之物鏡進行量測，於1269 nm 測得
TM 偏振光12.76% 的反射率最低值，而TE 偏振光的反射率為90.21%，顯示了良好
的偏振選擇性。最後於波長1269 nm、光功率0.53934 mW、偏壓6.77 mV 操作條件下進行元件之電性量測，量得光響應度為4.39649 mA W−1，外部量子效率（EQE）
為0.42955%，NEP （noise equivalent power）為5.059446 × 10-9 W/√(Hz)，偵測率D∗ (specific detectivity) 為7.654956 × 10^6 Jones。另一方面，元件響應特性呈現出強烈的光功率反比效應，且在不同偏壓下呈現正／負光導雙重行為。我們以COMSOL
Multiphysics 模擬具底層銀之銀光柵最佳化設計之元件，以模擬數據對金屬光柵內部電
場分量以及相位進行分析並對實際量測展現出的正負光導轉換行為進行初步的解釋。
整體而言，本研究對最佳化設計元件進行了完整的數值模擬與實驗量測，雖然實際
製程的元件最終外部量子效率表現並不理想，但量測結果展現的穩定且可重現性已驗證
其作為高速、低功耗光偵測平台之潛力。
;In recent years, with the rapid development of high-speed optical communication
technology, the demand for highly efficient photodetectors operating in the near-infrared
(NIR) regime has become increasingly urgent. In this spectral range, the most mature
technologies are based on InGaAs PIN photodiodes and avalanche photodiodes, which
exhibit excellent linear response and high sensitivity. However, their reliance on III–V
materials results in high fabrication costs, complex processes, and poor compatibility with
CMOS integration, issues that are becoming progressively more prominent.
Against this backdrop, negative photoconductance (NPC) photodetectors have emerged
as a novel research direction in recent years, owing to their advantages of simple fabrication
and low material cost. In this study, a near-infrared photodetector based on a metallic
nanoscale surface-relief grating with tunable photoconductive properties was designed and
fabricated, targeting the optical communication band (1303.5–1310 nm). The device was
engineered to exhibit both high absorption efficiency and negative photoconductance, with
its structural design incorporating surface plasmon resonance (SPR) and Fabry–Pérot resonance
to further enhance local field intensity and improve performance. Finally, numerical
simulations and parameter optimization were carried out using the particle swarm optimization
(PSO) algorithm implemented in Lumerical FDTD Solutions, achieving internal
absorption rates of 60.14% and 60.37% within the metallic grating at wavelengths of 1308
nm and 1315.5 nm, respectively, under TM-polarized light incidence.
For the temporal response analysis, Lumerical FDTD simulations were performed at representative points within the metallic grating under both single-pulse and three-pulse sequences. The results demonstrated that the optimized silver-backed metallic grating
is capable of detecting optical signals up to a theoretical limit of approximately 2 Tbps,
fully meeting the demands of current high-speed optical communication and showing great
potential for future developments.
Experimentally, the optimized silver-backed grating device (denoted as S1106D4)
was fabricated and characterized using a microscope-based reflection measurement system
equipped with a 10× objective lens (NA = 0.3). The minimum reflectance for
TM-polarized light was measured to be 12.76% at 1269 nm, while the reflectance under
TE polarization was as high as 90.21%, indicating excellent polarization selectivity.
Furthermore, under operating conditions of 1269 nm incident wavelength, optical
power of 0.53934 mW, and applied bias of 6.77 mV, the device exhibited a responsivity of
4.39649 mA W−1, an external quantum efficiency (EQE) of 0.42955%, a noise equivalent
power (NEP) of 5.059446 × 10−9 W/√Hz, and a specific detectivity D∗ of 7.654956 × 10^6
Jones. In addition, the device displayed a pronounced inverse dependence on incident
optical power and demonstrated a dual behavior of positive and negative photoconductance
under different applied biases. COMSOL Multiphysics simulations of the optimized
silver-backed grating were further performed to analyze the internal electric field distribution
and phase response, providing preliminary insights into the experimentally observed
positive-to-negative photoconductance transitions.
Overall, this study has demonstrated a comprehensive design-to-experiment workflow
for an optimized metallic grating photodetector. Although the final external quantum efficiency
was not ideal, the stable and reproducible measurement results verify the potential
of such a platform for high-speed, low-power optical detection applications. |
