| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 106 === In this thesis, we study gallium arsenide (GaAs) and hot electron based Schottky diode of photodetector performing broadband detection capability working from extreme ultraviolet (EUV) to near-infrared (NIR) regime. This study demonstrated the hot electrons generated in structured gold (Au) or molybdenum (Mo) electrodes and propagating to metal/ semiconductor (GaAs) junction can be used for optical-electrical signal conversion for detecting light with photon energies below the bandgap of the semiconductor, especially in the spectral regime for optical telecommunication. Furthermore, we investigated the optical properties of GaAs and metal films in the EUV spectral regime to demonstrate a low power consumption of photodetector having an ultra-broadband detection ability.
In the first part of this thesis, metal (Au, Mo)/ semiconductor (GaAs) based Schottky junction photodetector has been designed for hot electron collection from deep-trench/ thin metal (DTTM) based active antenna which takes the advantage of surface plasmon resonance and three-dimensional cavity effects. The DTTM-based devices have attractive properties of low reflection and high absorption in the near-infrared (NIR) regime, which enables the GaAs based devices breaking the limitation of bandgap of 870 nm (1.42 eV), extending its detection capability to the spectral regime of optical communication wavelengths of 1310 nm and 1550 nm. Taking the Mo/GaAs DTTM device as an example, the photocurrent responsivities at 1310 nm and 1550 nm are 0.27 mA/W and 0.16 mA/W, respectively, which is an order of magnitude smaller than that of the Si-based DTTM device. However, in terms of photovoltage detection, the response of the Mo/GaAs DTTM device at 1310 nm and 1550 nm are 577.47 (V/W) and 435.15 (V/W), respectively, which is 10,000 times larger than the photoelectric response of a Si-based DTTM device. We suggested that the photovoltage
responsivity is significant for the high resistance and trap density of GaAs substrate.
In the second part of this thesis, the concept of backside-illuminated schemes of metal (Au or Mo) film along with GaAs based DTTM structure were proposed. Compared with the front-illuminated devices, the backside-illuminated devices have three main advantages: (1) Hot carriers could be effectively generated and effective collection. (2) Devices performed broadband absorption covering the wavelengths of 1310 nm and 1550 nm, (3) Devices performance were not sensitive to the angle of incident performing omnidirectional detection properties. The measured results demonstrated that the responsivity of photocurrent and photovoltage are much higher than those of the front-illuminated devices. In the case of Mo/GaAs DTTM device, the photocurrent responsivity of the back-illuminated type are 0.95 mA/W and 0.25 mA/W at 1310 nm and 1550 nm, respectively, and the photovoltage responsivity are 781.52 (V/W) and 540.96 (V/W), respectively.
In the third part of this thesis, because of high transmission at the wavelength of 13.5 nm, we suggested Mo is a suitable metal as the front electrode of Schottky photodetectors in the EUV spectral regime. Moreover, GaAs has a high absorption coefficient compared to Si in the EUV regime. Therefore, it is considered that Mo/GaAs-based Schottky diodes have a good opportunity to be used as a superior photodetectors working in EUV regime. In this study, we extended the Mo/GaAs DTTM devices operating in the EUV regime. Because of high resistance of GaAs substrate, the generated excess photocurrent in the EUV regime is much smaller than that of the Si-based photodetector.
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