;Recently, infrared photodetectors have attracted much attention because of the development of optical communication system. Although infrared photodetectors have been built in III-V compound semiconductors, the use of SiGe is advantageous in terms of compatibility with Si integrated circuit technology and lower cost of fabrication. Several techniques for growing epi-SiGe photodetector have been reported. However, high temperature (>500oC) growth is disadvantage for device fabrication and more expensive, so in order to solve this problem, many researches have been doing efforts to grow the SiGe films and photodetector under low substrate temperature. In this thesis, we use the electron cyclotron resonance chemical vapor deposition (ECR-CVD) to deposit high-crystallinity SiGe thin films at a low temperature and apply it to fabricate phtodetector. During film deposition, We use optical emission spectroscopy (OES) to monitor the plasma distribution where the Ge*/(Si*+Ge*) can be predicted the germanium content in the SiGe films and the Hα*/(SiH*+GeH*) intensity ratio represents the trend of films crystallinity. As the Ge fraction increase from 0 to 0.58, the optical bandgap decreases from 2 eV to 1.4 eV. When the microwave power is 1000 W and hydrogen dilution ratio is 40, respectively, the films has best crystallinity. The requirement of photodetector are high responsivity and low dark current .The reduction of dark current can be improve by reduction of defect in the film and interface. With 300 oC annealing process for 5 minutes, the dark current was significant reduced from 2.27×10-5 A to 7.41×10-6 A. It was found that as germanium content increase from 0 to 0.58, the responsivity increase from 0.034 A/W to 0.195 A/W.