- 學位論文
超寬波段之低耗能矽基紅外光偵測器研究
Study of Silicon Based Infrared Photodetectors with Low Power Consumption and Ultrabroadband Working Capability
摘要
本論文的目的在於開發寬波段且低耗能之紅外光偵測器。論文第一部分，提出背面照射式元件，藉由表面電漿共振現象與共振腔效應有效提升矽化鎳（nickel silicide, NiSi）元件於近紅外光波段的光學吸收值。表面電漿共振的衰逝波可激發矽化鎳內部的熱電子（hot electrons），使矽基元件在光子能量小於矽的間階能隙（Eg≈1.124 電子伏特）之光通訊波段仍可操作。熱電子的光電響應趨勢會遵守Fowler theory，隨著光子能量越小，元件的光響應度亦隨之變弱。矽化鎳/n型矽基板的蕭特基能障（Schottky barrier height, Ф_B）為0.65電子伏特，較低的蕭特基能障預期會有較高的光電流響應，但也會有暗電流過大、弱光偵測能力不佳等問題。因此，藉由離子佈植二氟化硼離子（BF2+）於n型矽基板，調高矽化鎳/n型矽基板的蕭特基能障，使熱電子無法跨越過蕭特基能障並累積在接面兩端，有利於電壓響應輸出，並分別討論元件在電流模式、電壓模式操作下，離子佈植的最佳化條件。當摻雜劑量為2x1012 ions/cm2二氟化硼離子到n型矽基板時，外加0.0025V偏壓，元件在1310奈米、1550奈米之光電流響應度分別高達14.01 mAW-1、10.83 mAW-1。當摻雜劑量為2x1014 ions/cm2之二氟化硼離子到n型矽基板時，元件位於1310奈米、1550奈米之光電壓響應度分別高達20.14 VW-1、13.89 VW-1。元件的光電壓輸出於弱光與強光下皆具有極佳的線性程度，具良好弱光偵測的能力。 從Folwer theory可知，當入射光的光子能量小於蕭特基能障，將無法貢獻光電流響應達到光偵測效果，金/n型矽基板的蕭特基能障為0.75電子伏特，亦即波長超過1650奈米將無法有效產生光電流，達到光偵測的目的。本論文的第二部分，我們提出正面照射式之超淺溝槽矽基結構元件，藉由表面電漿現象用下，使元件於3.25微米之共振波段具有窄波段、高吸收的特性。於光學模擬上，元件的模擬吸收峰值可高達95 %，吸收峰值的半高波寬約為50奈米，窄波段吸收的特性使得元件僅對於設計波段之入射光能有所反應，，將可避免接收其他波段之入射光能所造成的訊號誤判情況發生。當金屬吸收大量的入射光後，金屬膜的溫度上升並進而加熱金/n型矽基板的蕭特基接面，激發矽基板的價帶電子躍遷至導帶使接面兩端產生電壓差，進而貢獻光電壓響應;光學的高吸收特性也會使金屬內部產生大量光激發熱電子累積在接面兩端，產生光電壓響應。因此，即使入射光能量小於金/n型矽的蕭特基能障，在上述兩種效應的貢獻下，我們依然可以藉由光電壓輸出來達到紅外光偵測的目標，不被Fowler theory限制。於光電轉換特性上，當外加2.5mV之小偏壓，光電流響應度可達2.5x10-3 mAW-1;光電壓響應度則可達250 mVW-1。；此外，元件於弱光或強光照射下具有極佳的線性度，可偵測最低入射光功率密度為0.69 mW cm-2。 論文第三部分將延續前述的工作原理，並進一步提出背面照射元件架構之中紅外光偵測器。和第二部分的元件相比，此部分我們所提出之背面照射式深溝槽矽基結構元件具有寬波段、高吸收的特性，於模擬上，元件於3.25微米至10微米的吸收值皆可大於50 %，此種寬波段吸收之特性使得元件的工作波段可從3.25微米延伸至10微米，具有寬波段光能回收之能力。於光電轉換特性上，此元件於波長3.25微米、6微米、10微米之光電壓/光電流響應度分別為42.01mVW-1/2.23×10-3 mAW-1、28.05 mVW-1/4.4×10-3 mA W-1、76.2 mVW-1/7.80×10-3 mA W-1，展現出極寬波段之偵測能力；此外，當入射光波長為10微米時，其於弱光或強光照射下皆有不錯的線性程度，可量測到最低入射光功率密度為為1.71mW cm-2。於論文的第二、三部分所提出之元件光電量測皆於室溫下進行，符合低耗能之期許。
並列摘要
The goal of this thesis is to develop the infrared (IR) photodetectors featuring low power consumption and capability of detecting over broad bandwidth. In the first part of thesis, we propose back-illuminated devices that take advantage of surface plasmon resonance phenomena and three-dimensional cavity effects to improve the optical absorption of deep trenched nickel silicide/n-silicon devices in near infrared (NIR) regime. The devices exhibit good rectification properties to collect hot electrons arising from plasmon decay for photodetection well below the bandgap of silicon. In general, the spectral response of hot electron-based device follows Fowler theory. The responsivity becomes lower as the photon energy of incident light decreased. The Schottky barrier height of original NiSi/n-Si device is approximately 0.65eV. Such low barrier height of structured device performed photocurrent-responsivity in IR regime. However, devices also perform high dark current that exhibit insufficient detection capability. Therefore, we propose the BF2+ ion implantation process to dope Si for tuning the barrier height of NiSi/n-Si-based device. As the barrier height of devices increased, the dark current of device would decrease and more photo-induced hot electron would accumulate near the junction instead of passing the barrier. Therefore, the doped devices could perform high detectivity and photovoltage. In this thesis, we also investigate the optimized conditions of implantation in NiSi/n-Si-based devices. As we doped 2x1012 ions/cm2 in n-Si wafer, under 2.5mV bias voltage, the responsivity of devices in current mode are up to 14.01 mA W-1 and 10.83 mA W-1 in 1310nm and 1550nm, respectively. As we doped 2x1014 ions/cm2 in n-Si wafer, the responsivity of devices in voltage mode are up to 20.14 V W-1 and 13.89 V W-1 in 1310nm and 1550nm, respectively. Besides, the devices also perform a high degree of photo-response linearity. According to the Fowler theory, the hot electrons cannot contribute photocurrent if the energy of incidental photon is lower the Schottky barrier height of devices. For example, the Schottky barrier height of Au/n-Si is approximately 0.75eV. The incident light having a wavelength longer than 1650nm cannot contribute the photocurrent. In the second part of thesis, we propose the front-illuminated devices of shallow trench/thin metal (STTM) structures for photodection in mid IR regime. The STTM devices take advantage of SPR effect to tune absorption peak in infrared regime. In optical simulation, the absorption of devices could up to 95%, the full width at half maximum (FWHM) of absorption peak is approximately 50nm. The characteristic of high absorption in narrowband is useful for photodetection of incident light in the resonance of spectral regime. After the metal layer absorb mid IR light efficiently, the temperature of metal layer would be increased, the Au/n-Si Schottky was heated and generate the difference of voltage near the junction. According to the Fowler theory, the photo-induced hot electron accumulate near the junction instead of passing the Schottky barrier, contributing photovoltage near the junction. Based on above discussion of photovoltage, the detection bandwidth would not restrict by Fowler theory. We can extend the detection bandwidth to 3.25 µm. With 2.5mV bias voltage, the photocurrent-responsivity of device is 2.5x10-3 mA W-1 in 3.25µm. The voltage-responsivity of device can up to 250 mV W-1. The devices also show linear photovoltage-response in not only high power of incident light region but also the low-intensity detection is 0.69 mWcm-2 at the wavelength of 3.25µm. In the third part of thesis, we extend the working mechanism in the second part of thesis, we propose the back-illuminated devices of deep trench/thin metal (DTTM). Compared with the devices in the second part of thesis, the back-illuminated DTTM devices display broadband and high absorption in mid IR regime. In optical simulation, the absorption of DTTM is higher than 50% from 3.25 µm to 10µm, so we can extend the detection bandwidth from 3.25 µm to 10µm. The devices show the ultra-broadband working capability. The photovoltage/photocurrent-responsivity mode can up to 42.01mVW-1/2.23×10-3 mAW-1, 28.05 mVW-1/4.4×10-3 mA W-1, 76.2 mVW-1/7.80×10-3 mA W-1 at the wavelength of 3.25µm, 6µm, 10µm respectively. The devices also show linear photovoltage-response in not only in high intensity of incident light but also low power of incident region and the low-intensity detection is 1.71 mWcm-2 at the wavelength 10µm. Additionally, the devices can work at room temperature (T=300 K), which reach expectation of low power consumption.