| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 105 === 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.
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