紫外至近紅外光波段之高效率低耗能奈米結構光偵測器之研究

Abstract

光偵測器已廣泛運用在影像感測、光通訊、環境監控、太空偵測、光譜儀、及生醫感測等領域。然而光偵測器為操作偏壓大、可偵測之光譜範圍限制與弱光偵測能力不足等限制了它實際的應用性。本論文即針對上述之限制提出改善方案，分別針對偵測紫外光(單一波段)、可見光至近紅外光(涵蓋兩個波段)及紫外光至近紅外光波段(涵蓋三個波段)之光偵測器進行研究。 論文第一部份針對紫外光偵測器進行開發，藉由準分子雷射退火技術，大幅的改善氧化鋅(Zinc oxide)薄膜於極淺層的結晶性，元件只需外加10毫伏特(mV)偏壓即可正常操作，使氧化鋅光導體於弱光下達到0.38 fW 〖μm〗^(-2)光電響應。 論文第二部分我們將鋁摻氧化鋅(Aluminum-doped Zinc Oxide, AZO)透明導電薄膜與氧化鋅奈米柱結構(zinc oxide nanorod)組成複合式抗反射透明電極，並利用鋁摻氧化鋅薄膜能與矽基板形成具良好整流效果之蕭特基接面(Schottky junction)，成功的製作出可見光至近紅外光於零伏操作下即具有高光電轉換效率的光偵測器，此元件具有不會受到入射角度的改變而影響效能之高光電流響應度(R＝0.59 A/W, λ＝850 nm)且具有高光電壓響應度(R_V＝8,200 V/W, λ＝850 nm)。此外，元件本身因氧化鋅奈米柱結構而具備自潔效果。 論文第三部分研究紫外光、可見光至近紅外光波段(涵蓋三種波段)操作之光偵測器，本論文提出於矽基板上製作出一個倒錐狀深溝槽結構(Inverse-cone deep-trench structure)並披覆連續銀薄膜之設計來達成，此矽奈米結構披覆銀薄膜具有多重功能: 光偵測器之電極、三維大面積蕭特基接面及涵蓋紫外光至近紅外光波段三種波段內之光學低反射層。更可提供光學高穿透於寬波段使其具備弱光偵測能力，以及高外部量子效率 (External quantum efficiency, EQE)。此元件於寬波段範圍內EQE皆大於60 %。特別值得一提的是，此光偵測器可於零伏偏壓條件下操作且對入射光極化型態不敏感。此元件也相容於成熟之互補式金氧半(Complementary Metal-Oxide-Semiconductor, CMOS)製程，可以低成本且快速地製作出數百奈米尺度深溝槽狀的薄層連續金屬結構為基礎之低耗能光偵測器。

Photo-detectors have been applied in wide range of applications, such as image sensing, optical communication, environmental monitoring, astronomical studies, spectrometer, and medical therapy. However, large bias voltage, narrowband of sensing spectral and insufficient detection capability limited the practical applications of detectors. In this thesis, some techniques and specific nanostructures were proposed for improving the performances of photodetectors. The first part of thesis was focused on photodetector working in the ultraviolet (UV) range. A KrF excimer laser was used to rapidly anneal and largely improve the crystallinity of zinc oxide (ZnO) film within ultrashallow region, thereby enhancing the photoresponse of ZnO-based photoconductors. Moreover, the laser annealing process has successfully improved the photoresponse of ZnO photoconductor at low power density of 0.38 fW 〖μm〗^(-2) by only applying 10 mV of bias voltage. In the second part of thesis, we combined an aluminum-doped zinc oxide (AZO) film with ZnO nanorods to construct a hybrid anti-reflection of transparent electrode. Since the AZO could form a rectifying Schottky contact with n-type silicon (Si), we fabricate a Schottky photodiode with broadband photoresponse from visible to near-infrared (NIR) regime. The photodetector exhibited high photoelectric conversion efficiency without applying any bias. At the wavelength of 850 nm, the photoresponsivity of detector was 0.59 A/W, and the photovoltage responsivity was 8,200 V/W. Moreover, the photodetector exhibited omnidirectional light-harvesting ability, and the hydrophobic surface of the nanorod based photodetector performed a great self-cleaning ability. In the third part of thesis, we demonstrated an inverse-tapered deep-trench Si structure covering with a continuous thin metal film that can be used a superior photodetector working from the UV to NIR spectral region. This corrugated metal film on Si plays the important role of (1) the conducting electrode of photodetector, (2) large area of three dimensional Schottky junction, and (3) low reflectance of metal film ranging over the UV to NIR regime. The multifunctional structured metal film form a well rectifying Schottky contact with Si substrate, it greatly enhanced the external quantum efficiency of Si in the UV regime up to 60 % and also enhance the corresponding low-light detection capability under zero bias voltage. It is worth to note that this strategy exhibit high responsivity under zero bias voltage, while preserve the advantage of polarization-insensitive detection. The device can be easily fabricated by the mature and low-cost Si-based processes.