Infrared (IR) photodetector is widespread applied to spectroscopy, biosensing, and image detection. Nowadays, most of IR photodetectors are prepared from compound semiconductors, for example, SiGe, HgCdTe, and InSb. However, most of them are formed through high energy consumption and high expense processes, such as chemical vapor deposition. Also, compound devices are not compatible with Si-based IC manufacturing and very expensive. Therefore, here, we used n-type Si (n-Si) wafers and Ag thin films to form a Schottky IR detector. The detection principle is using IR source to induce thermionic effect on Schottky diode and then the scattering of photoelectrons excited by IR and visible light, respectively, induces current difference. Regarding device preparation, at first, the native oxide on n-Si wafers was removed by buffer HF; then the 10-nm-thick Ag films and 100-nm-thick Ag grid anode were thermally deposited on the n-Si successively. Afterward, Al was thermally deposited on the opposite side of n-Si wafers to be a cathode. The electric property of devices was determined through current-to-time (I-T) measurement with an 80-mW green laser illuminating on the Ag side constantly. A 3.22-μm IR source was illuminated through Ag side but turned on/off for each 5 s. The electric bias is 0 V. Consequently, if no green laser exposing, current increased after IR turned on due to the pure thermionic effect and the responsivity is 1.8 mA/W. While the green laser illuminating constantly, current decreased after IR turned on, and the responsivity increased to -15.7 mA/W.