| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 102 === In this research, we use the electron cyclotron resonance chemical vapor deposition (ECR-CVD) to grow epitaxial germanium (Ge) thin films on single crystal silicon substrates (c-Si) and applied to the photodetector at a low temperature. Compared to Si, Ge has smaller energy band gap and higher carrier mobility, and therefore the bulk Ge is often used in the field of silicon photonics and high efficiency III-V multi-junction solar cells. The cutoff wavelength of Ge is at 1550 nm, so Ge can be used as a near-infrared photodetector. However, the cost of c-Ge is about 4 times higher than that of c-Si, so in order to reduce the cost, many researches have been doing efforts to grow high quality epitaxial Ge films on silicon substrates to replace c-Ge substrates. In this work, we use ECR-CVD to deposit epitaxial Ge on c-Si at a low temperature of 180 oC and further use rapid thermal annealing (RTA) process to improve epitaxial quality and applied it to the photodetector.
In this investigation, we analyze the effect of different parameters on the films quality. We use optical emission spectroscopy (OES) to in-situ monitor the plasma distribution during film growth and use Ellipsometry (SE), Raman Spectrometer, and X-ray Diffractometer (XRD) to characterize the thin films properties. The result shows that the XRD full width at half maximum (FWHM) of 683 arcsec can be obtained when the film thickness is 100 nm. The responsivity of photodetector in 850 nm light source is 0.2 A/W at -1V and 0.42 A/W at -3V. In 1310 nm light source, the responsivity is 0.07 A/W at -1V and 0.139 A/W at -3V. After annealing, we can reduce the dark current density to 1.89 mA/cm2.
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