極寬波段之高效率低耗能之金屬矽化物/矽基光偵測器研究

Abstract

光偵測器已廣泛運用在光通訊、影像感測、太空監測、環境監控及生醫感測等領域。然而，傳統光偵測器因操作偏壓大、可偵測之有效光頻譜範圍限制、弱光偵測能力不足及在紅外光波段需額外搭載冷卻系統等限制了此類元件實際之應用。本論文將針對上述之限制提出改善方案，循序開發可見光至通訊波段紅外光之寬波段 (broadband) 金屬矽化物/矽基光偵測器，並藉由背面照射偵測光架構成功提升其在光通訊波段之光電轉換效益，並將此金屬矽化物/矽基光偵測器延伸至中紅外光波段 (middle infrared band) 操作。使矽基光偵測器在光子能量小於其間階能隙 (Eg≈1.124 eV) 之波段亦能具有光偵測之可能性。 論文第一部分建立了所需之製程參數與材料光學常數，以利後續章節光偵測元件之光學設計和製作。首先，以材料其表面電漿子之觀點，NiSi 相在紅外光波段的光學吸收效益將比金和銀更具優勢。再者，藉由低溫、短秒數之熱退火製程參數，將有效降低矽化鎳與矽晶圓所產生的蕭特基二極體其接面漏流密度。因此，NiSi非常適合開發為可見光至紅外光波段之寬波段蕭特基光二極體偵測器。 論文第二部分將針對可見光至光通訊波段之光偵測器進行探討，利用連續矽化鎳薄膜之深溝槽矽基結構使其能在共振波段產生光學低反射、高吸收和對於偏振態不敏感之光學特性及三維大面積蕭特基接面和光偵測器之電極。元件在零伏外加偏壓操作時，在通訊波段光波長為1310奈米與1550 奈米時，其光激發熱載子之光響應度可高達2.78 mA W-1與1.34 mA W-1；且在弱光或強光底下其決定係數(R2)皆能維持在0.999，並可量測到最低入射光功率密度為41 fW μm-2和75 fW μm-2。此外，此矽化鎳/矽基光偵測器元件在可見光至近紅外光波段 (λ=350~1100 奈米)亦可由矽基間接能隙吸收光子，因此具備寬波段 (λ=350~1800 奈米) 之光偵測能力。 論文第三部分我們藉由偵測光由背面照射元件之架構，成功的提升了矽化鎳薄膜在矽基上的光學特性，使其能夠在近紅外光寬波段(通訊波段)產生光學低反射、高吸收之特性。且因光子進入矽化鎳薄膜內部極淺距離即被大量吸收，因此光激發熱載子離蕭特基接面較近，在通訊波段光波長為1310奈米與1550 奈米且零伏外加偏壓操作之下，其光響應度可高達3.83 mA W-1與2.60 mA W-1；在弱光或強光底下其決定係數皆能維持在0.999，並可量測到最低入射光功率密度為24 fW μm-2和38 fW μm-2。特別值得一提的是，此光偵測器結構為六方最密排列，因此具有對於偏振態角度不敏感之特性。 論文第四部分，成功的結合了矽化鎳薄膜與深溝槽矽基結構，使其能在中紅外光共振波段產生光學低反射、高吸收特性，進而加熱蕭特基二極體接面產生光電壓。此元件在中紅外光波段光波長為10.6微米時，其光響應度可高達31 mV W-1，可量測到最低入射光功率密度為1.2 nW μm-2，且具高度再現性。此光偵測器能針對特定波長之偵測光進行光偵測，較不易受環境雜訊干擾，導致訊號誤判。元件之量測架構皆在室溫下進行，因不須額外搭載冷卻系統，故能符合低耗能之期許。 綜合上述之結論，我們成功開發出可見光、光通訊波段至中紅外光波段之高效能低耗能之矽化鎳深溝槽矽基結構之矽化鎳/矽基光偵測器。具有零伏外加偏壓及室溫操作之節能特性，以及製程簡易且相容於成熟之矽互補式金氧半(Complementary Metal-Oxide-Semiconductor, CMOS) 製程，具可快速量產優勢。

Nowadays, photodetectors have been widely used in the field of optical communication, image sensing, astronomical studies, environmental monitoring, and medical therapies. In general, photodetectors present several notable challenges in applications, such as operating at large bias voltage, using extra cooling system for infrared ray detection, and insufficient detection capability. In this thesis, we proposed optical techniques and specific nanostructures to develop the metal silicide/silicon (Si) based photodetectors operating from visible to optical tele-communication regime. Moreover, we successfully improve the photoelectric conversion efficiency in optical telecommunication regime by back-illuminated setup. Finally, we successfully extend the detection capability of the metal silicide/ Si based photodetectors to mid-infrared regime. In the first part of thesis, we developed the manufacture processes and found the optical constants of nickel silicide (NiSi) for the following research. First, we simulated and found the optical absorptance of nickel silicide (NiSi) is superior to noble materials, such as gold and silver, in the infrared regime. Second, low annealing temperature and short annealing time for the preparation of NiSi would be conducive to reduce the leakage current density of the NiSi/ Si Schottky diode. Therefore, NiSi is a suitable candidate for developing broadband Schottky barrier-based photodetectors from visible to infrared regime. In the second part of the thesis, we demonstrated a deep trench Si structure covered with a continuous thin NiSi film that could provide low reflectance, high absorptance and polarization-insensitive detection, Moreover, large area of three dimensional NiSi/Si based Schottky junction and electrode is an important feature of the photodetector. Under zero bias voltage, the responsivity of the device can up to 2.78 mA W-1 and 1.34 mA W-1 . The detection capability for low-intensity light at optical telecommunication wavelengths of 1310 nm and 1550 nm are 41 fW μm-2 and 75 fW μm-2, respectively. Moreover, the device demonstrated a linear response (R2=0.999) at optical telecommunication wavelengths and could also detect the light from visible to near infrered regime (λ=350~1100 nm) by the indirect band gap of Si. Therefore, the deep trenched NiSi/Si devices could perform broadband detection capability (λ=350~1800 nm). In the third part of thesis, we demonstrate a back-illuminated setup in order to enhance the optical performance of deep trenched NiSi/Si devices, such as low reflectance and high absorptance in the optical telecommunication regime. The devices could provide high responsivity and low-intensity detection capability owing to the incident photon would be absorbed quickly and effectively in the very shallow region of NiSi, and the generated hot carriers would be very closed to the Schottky junction. Therefore, under zero bias voltage, the responsivity of the back-illuminated device could up to 3.83 mA W-1 and 2.60 mA W-1 and the low-intensity detection capability were 24 fW μm-2 and 38 fW μm-2 at the wavelengths of 1310 nm and 1550 nm, respectively. The back-illuminated device also exhibited a linear photo-response (R2=0.999). It’s worth to note that the device is polarization-insensitive owing to the structure with hexagonal closest array. In the fourth part of thesis, we successfully combined the nickel silicide thin film and deep trenched structure to construct a mid-infrared NiSi/Si-based photodetector. In the resonance spectral regime, the device could perform low reflectance and high absorptance that is benefited to heat the Schottky junction and generate photovoltage. Therefore, under zero bias voltage, the responsivity of the device could up to 31mV W-1 and the low-intensity detection capability was 1.2 nW μm-2 at the wavelength of 10.6 μm. The device could selectively detect the specific wavelengths of light by adjusting the dimension of the deep trenched structures. It is worth mentioning that the device could work with low power consumption under room temperature without cooling system. In conclusion, we successfully develop deep-trench/ thin-silicide Si-based photodetectors for high efficiency and low power consumption from visible to optical telecommunication and mid-infrared regimes. Moreover, the devices are low power comsuption owing to operating under zero bias and room temperature. Furthermore, the fabrication processes of devices are compatible with mature Si-based CMOS fabrication technology.