Some effects of low-power ultraviolet radiation on silicon photodiodes

A short-term effect of low-power ultraviolet (UV) radiation on the widely used Hamamatsu S1337 photodiode is investigated. Experiments show that such photodiodes exposed to 248 nm radiation exhibit a 0,6% increase in responsivity at this wavelength, and a smaller increase at longer wavelengths. The increase is produced during the first tens of seconds of exposure and the new value reached by the responsivity remains stable even after further irradiation. The effect strongly depends on the wavelength of the radiation but is independent of power level within the measurement range of 8 µW to 50 µW. The surface reflectivity of the photodiode is not modified, indicating that radiation directly affects the internal quantum efficiency. It thus seems advisable to age this type of photodiode before calibration or simply to avoid any exposure to radiation below 300 nm.