矽基微奈米複合結構應用於寬波段紅外光偵測及熱輻射控制之研究

Study of broadband infrared photodetection and thermal radiation control on silicon based micro-nano hybrid structures

喻忠華(Chung-Hua Yu)

指導教授 ： 陳學禮

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201704188

摘要

中遠紅外光波段為大多數物質的吸收光譜指紋區，有利於材料之非破壞性快速檢測或是環境監測；此波段亦為室溫乃至數百攝氏溫度熱源之熱輻射波段，可以應用於熱成像領域，亦為熱輻射散熱之主要區域；而近紅外光波段則為光通訊波段，與現今資訊時代海量般的資訊傳遞密不可分，綜上所述，於紅外光波段無論是光偵測器、光源、或散熱途徑皆具有極高的實用價值，然而，目前此領域之研究大多面臨：製程氣體具毒性、成本較為昂貴且製程複雜、較難進行大面積製程、元件效率低落、耗能高且無法與現今之矽半導體製程技術 (Silicon-Complementary Metal-Oxide-Semiconductor, Si-CMOS)進行整合等種種問題。本論文將針對上述之限制提出改善方案，開發通訊波段紅外光矽基光偵測器並延伸至中紅外光波段，並藉由中紅外光波段寬波段高吸收之矽基結構增加熱輻射散熱。
論文第一部分結合了氮化鈦薄膜與深溝槽矽基結構，使其能夠在中紅外光共振波段產生光學低反射、高吸收特性，且連續氮化鈦薄膜能與 P型矽基板形成良好蕭特基二極體整流接面。在紅外光波段主要共振模態光波長為 10.6 微米時，光吸收值可高達 56.1% 左右，用以產生光電響應，以二氧化碳雷射(光強度=4.26W/cm2)量測時其光電壓響應度可達 0.632mV W-1，若在弱光(光強度=2.64mW/cm2)照射量測時更可達246 mV W-1。過剩電壓與光強度具有良好的線性關係，且量測具高度再現性，此元件之量測架構皆在室溫下進行 (T=300 K)，故能符合低耗能之期許。
論文第二部分將針對通訊波段之光偵測器進行探討，我們藉由背面照射元件之架構加上連續氮化鈦薄膜之深溝槽矽基結構，使其能夠在近紅外光寬波段且廣角度產生光學低反射、高吸收之特性。連續氮化鈦薄膜能與 P型矽基板形成良好蕭特基二極體整流接面，且光吸收產生載子處正好位於靠近接面處。在入射光波長為 1550 奈米時光吸收值可高達85.7% ，元件在零伏外加偏壓操作時，其光響應度可高達 0.412 mA W-1，偵測率為5.02 x109 Jones ，其在不同入射角方向之入射光入射時，光響應度變化極小，在60度以內皆保持光響應性達 0.372 mA W-1。另外，同時也利用光電壓的量測方式證實本研究元件電壓偵測模式之偵測能力達 15.4mV W-1 ，兩種偵測模式使光偵測器於光通訊應用端具有更大的彈性。
論文第三部分藉由連續氮化鈦薄膜之深溝槽矽基結構，成功的提升了氮化鈦薄膜在矽基材料上的光學吸收，使其能夠在中遠紅外光寬波段產生光學低反射、高吸收之特性，其高吸收特性同時也代表著高放射特性。經由實際元件光學量測結果，得知元件平均吸收值可高達 0.61。元件在室溫時，以氙燈系統發出之白光配合AM1.5濾片模擬之太陽光加熱，其平衡溫度與平膜元件之溫差高達8.5oC，衰減時間常數也少了3秒；不同尺寸結構之元件量測顯示溝槽深度高、孔洞/週期比例越接近1/3其平衡溫度越低，驗證了模擬上高吸收條件之結構平衡溫度較低，未來此研究概念可用於各式矽基元件熱輻射散熱之用。
論文第四部分，藉由連續金薄膜之淺溝槽二氧化矽基結構，成功的設計出於特定波段(4.3微米)具有窄波段高放射之元件，使其可以作為中紅外光波段之高品質因數 (Quality Factor,中心波長/半高波寬, Q= λ/Δλ)低耗能熱放射光源。另外，此結構之表面高電場特性亦可應用於表面增益紅外光吸收，使得二氧化碳吸收訊號在不改變吸收峰值比例的情況下使吸收訊號提升5.3倍。
綜合上述之結論，我們成功開發出通訊波段至中紅外光波段之高效能低耗能之氮化鈦深溝槽矽基結構之光偵測器、輻射散熱矽基結構及金淺溝槽二氧化矽基結構之中紅外光熱放射光源。其材料容易取得、製程簡易快速且相容於現行成熟之半導體製程，因此具低成本之商業量產優勢。

關鍵字

光偵測器 ； 輻射散熱 ； 熱放射 ； 氮化鈦 ； 光激發熱載子 ； 蕭特基光二極體 ； 中紅外光 ； 高品質因數 ； 低耗能

並列摘要

The infrared absorption spectrum in midinfrared (mid IR, MIR) spectral range contains “fingerprints” of the most common molecular bonds, key to sample composition analysis and is useful for nondestructive and rapid analysis for material characterization and environment monitoring. Furthermore, the MIR light can be applied to thermal image that is corresponding spectral regime for the thermal radiation from room temperature to several hundred degrees Celcius. On the other hand, near infrared (NIR) spectral range is the regime for optical telecommunication. To sum the above, photodetectors, light sources, and thermal dissipation routes in infrared spectral range all perform the importance in various applications. However, the study in this field so far faces several problems, including processes being complicated, slow, expensive, and not compatible with silicon semiconductor process technology (Si-CMOS, Silicon-Complementary Metal-Oxide-Semiconductor). This thesis would like to develop silicon-based photodetectors working from NIR to MIR regimes, Moreover, using the broadband, high absorption of silicon-based structures to develop thermal radiation based heat dissipation structures.
In the first part of this thesis, the titanium nitride (TiN) thin film coated on a deep trench silicon structure to generate low reflection and high absorption properties at resonace wavelengths. Also, TiN thin film can form a good Schottky contact with a p-Si substrate. When the resonanct wavelength at 10.6 μm, the optical absorption could be as high as 60.7%. The responsivity could be up to 0.632mV W-1 under CO2 laser (light intensity=4.26W/cm2) illumination and up to 246mV W-1 under low light intensity light source (light intensity=2.64mW/cm2). The excess voltage has great linear relationship with light intensity, and the measurement was highly repeatable. Also, the measurements were all conducted at room temperature which could satisfy the low energy comsumption demand.
In the second part of this thesis, we would like to develop photodetectors working in optical telecommunication spectral range. We used back illuminated schemes of TiN thin film along with deep trench silicon structure that can perform broadband, wide angle of low reflection, and high absorption properties. The optical absorption was up to 85.7% at 1550nm wavelength. TiN thin film formed a Schottky contact with p-Si substrates and the locations which carriers generated were close to the contact surfaces. When devices conducted at zero bias, the responsivity was up to 0.412 mA W-1, and detectivity was 5.02 x109 Jones. The responsivity of the devices differed very little when the angle of incident light below 60o. In addition, we also demonstrated the photovoltage detection ability of the devices and its responsivity was 15.4mV W-1.
In the the third part of this thesis, the TiN thin film and deep trench silicon structure performed broadband high absorption properties in MIR. The high absorption also represented the high emission property. By the optical measurement of practical devices, the average absorption was up to 61%. Use white light of Xe lamp along with AM1.5 filter in order to simulate solar light heating the devices. Its equilibrium temperature was lower 8.5oC than the flat film sample and the decay time constant of cooling was also 3 seconds shorter. The deeper trench, the closer the hole to period ratio (H/P) to 1/3, the lower the equilibrium temperature of the device, certificating that the high absorption conditions in simulations with lower equilibrium temperature.
In the the fourth part of this thesis, we used gold (Au) thin film combined with shallow trench silicon oxide (SiO2) and successfully designed a narrow band and high emission device at specific wavelength (4.3μm), making it a high quality factor (Peak wavelength/ Full width at half maximum, Q= λ/Δλ), low energy comsumption thermal emission light source in MIR. In addition, this structure could also apply to enhance the surface enhanced infrared absorption because of its high electric field on its surface. The structure made CO2 absorption signal enhanced 5.3 times without changing the absorption peak ratio of the two peaks of CO2.

並列關鍵字

photodetector ； radiation thermal dissipation ； thermal emission ； titanium nitride ； hot carrier ； Schottky photodiode ； mid-infrared ； high quality factor ； low power consumption

參考文獻

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