極寬紅外波段矽基光偵測器與高效能紅外光光源建構

Abstract

本論文主要探討材料於紅外光波段的應用，包含光偵測器與高放射率之紅外光光源。論文第一部分，將針對矽的能帶限制進行改善，矽半導體材料因其能隙較大，在紅外光偵測的應用受限，我們將利用五族離子佈值的方式高濃度摻雜於矽晶圓，藉由重摻雜矽中自由載子吸收的機制，應用其在長波段紅外光的吸收能力，結合金屬-氧化物-半導體的元件架構，製作寬波段紅外光矽基光偵測器。不同於過去蕭特基偵測器的操作，我們利用歐姆接面，在平衡狀態下，能帶會彎曲產生能帶谷，重摻雜矽之載子會累積於矽與氧化層之界面，元件在照射紅外光後，載子獲得能量進而穿隧氧化層，形成光穿隧電流與電壓訊號; 此外，偵測的紅外光是由矽晶背方向照射於元件上，光會先傳播於輕摻雜之矽介質中，此區域的矽對於紅外光是透明的。而矽大於空氣之折射率能使傳播中光的電磁場增加，最後提高在重摻雜矽區域的吸收性質，使其可達將近0.7的吸收率。元件在中紅外光2微米、3.25微米、6微米，10微米波段的光電壓響應度為10.09 mV/W、10.81 mV/W、16.88 mV/W、19.00 mV/W，皆不需再外加偏壓，室溫環境下操作，實現寬波段低耗能矽基中紅外光偵測之能力。 本論文第二部分將針對鎢金屬擴展其紅外光放射率以發展便宜之紅外光光源。鎢為常見的可見光照明材料，然而其在紅外光的放射率極低，當以高溫輻射時，在紅外光波段的能量會以熱的型態散失於環境中。我們將利用實驗室發展之週期性深溝槽的結構，僅以160奈米的鎢薄膜披覆於矽基板上，並利用矽晶背出光的方式大幅增加鎢在紅外光的放射率，尤其是波段1~25微米之輻射效率。在模擬上，我們可以由結構分別最佳化鎢在紅外光於廣波段以及特定波段的吸收，並根據克西荷夫定律之吸收率等於放射率，得到放射率從0.03提升至高於0.9的增益; 從實驗上我們由熱像儀與黑體膠帶校正元件之平均放射率，得到其平均放射率在8~13μm為0.7，經由量測得到鎢在紅外光的輻射能量確實由結構輔助而大幅的提升。最後將矽晶背進行介面處理，我們可以增加紅外光的光取出效益於3~5微米波段，再次的增加元件之吸收/放射率，其最高放射率接近0.9，符合模擬結果的預測。 本論文第三個部分，將針對重摻雜矽進行熱輻射的探討。其結合第一部份重摻雜矽之高吸收特性，以及第二部分鎢於矽晶背出光的方式，我們實際做出以全半導體材料整合之高放射率紅外光光源。因重摻雜矽在紅外光相較於金屬低的折射率低及較本質半導體高的消光係數，在模擬上我們發現，利用週期性深溝槽結構，重摻雜矽在紅外光波段也可以如同金屬，具有寬波段高吸收與高放射率的能力，其放射率在8~14微米波段可達將近0.9。在實驗上我們同樣以熱像儀及黑體膠帶為校正工具，校正過後之平均放射率在8~13μm為0.69，並經由能量的量測結果得到，重摻雜矽在紅外光的輻射能量也能因結構而大幅提升。最後經由比較二、三部分的元件，鎢結構元件在1~25μm之平均放射率為0.628，而重摻雜矽結構元件之平均放射率為0.603，相較於平膜元件皆具極寬波段且高的放射率增益。綜觀上述，我們將常見的材料，如重摻雜矽以及鎢，整合於半導體製程中，並擴展矽基元件在紅外光偵測及放射的能力，發展便宜、節能且高效率之紅外光系統。

In this thesis, we study the silicon (Si) based devices working in the infrared (IR) regime, including broadband IR photodetector and IR light source (emitter) with high emissivity. In the first part of the thesis, we focus on overcoming the limitation of Si band gap for broadband IR photodetection. We useed an ion implantation process on structured Si to fabricate a heavily doped Si layer. The mechanism of free carrier absorption in heavily doped Si increases the absorption of Si in the IR regime. In this thesis, we investigate the broadband Si based IR detector by integrating metal-insulator-semiconductor (MIS) structure with a heavily doped Si layer on a structured Si substrate. Different from the previous studies of Si-based IR photodetectors, which used the mechanism of Shottcky junction, we apply the band valley of ohmic junction to accumulate free carriers near the interface of Si and insulator (oxide). As the ohmic junction reaching the thermal equilibrium condition, the band valley would be formed by the band bending effect of the junction. By illuminating with IR light, the carrier would tunnel through the oxide layer to perform photoresponse. Moreover, the IR light illuminated into the backside of Si and can pass through lightly-doped Si substrate. Because the refractive index of Si is larger than that of air, the light passing through the lightly doped region can enhance the electromagnetic field of light, further increasing the absorption of the device. The measured absorption of the device can be up to 0.7. Furthermore, the device can operate at the wavelengths of 2μm, 3.25μm, 6μm, and 10μm IR bands and the photo-voltage-response is 10.09 mV/W, 10.81 mV/W, 16.88mV/W, 19.00 mV/W, respectively. The devices can operate at room temperature and without any bias voltage , achieving the goal of developing a Si-based infrared photodetector with low power consumption and broadband working capability. In the second part of the thesis, we focus on extending and increasing the emissivity of tungsten from near IR (NIR) to mid IR (MIR) spectral regimes in order to develop a broadband and low cost IR emitter. Tungsten is a common material used in visible light illumination for a long time. The drawback is that the emissivity of tungsten is very low in the broad IR regime. We develop the periodical deep trench and cover it with only 160nm of tungsten film. By using the light emitting from backside of Si, we are able to significantly enhance the emissivity of tungsten in the broadband regime from 1 to 25μm. In the simulation, we use the structure of periodical deep trenches to enhance the average absorption of tungsten to 0.9 in the broad infrared band. In the experiment, we use black tape and thermal imager to calibrate the emissivity of our device, and the average emissivity is about 0.7 at 8~13μm. The experimental result demonstrate that the radiation energy of the device largely enhanced by the structure. By coating the antireflective layer on the backside of Si, the absorption/emissivity of the device further increased to close to 0.9. In the third part of the thesis, the thermal radiation properties of heavily doped on structured Si wafer were investigated. We developed an all-Si based device that can be used as an IR emitter by combining the the property of high absorption of heavily doped Si and the optimal trenched structures. In the optical simulation, we found that heavily doped Si performing high absorption/emissivity up to 0.9 in the 8-14μm spectral regime. In the experiment, the average emissivity of 0.69 at 8~13μm spectral regime was demonstrated. The result shows the radiation energy of heavily doped Si based IR emitter can be largely enhanced by the structure as well.