Thermal drift reduction in photodiode dosimeters with switching bias.

• Commercial photodiodes as radiation sensors. • Thermal characterization and thermal model: With reverse bias current the device acts as photodiode, and applying forward bias current and playing as pin diode. • The forward voltage of the pin diode results proportional to silicon die temperature, as it was expected. • Radiation measurements were thermal compensated using the thermal model, and as input the forward voltage of the diode. • The presented thermal compensation method permits to reduce the uncertainty of the radiation measurements using photodiodes due to temperature. The effect of temperature on dosimetric measurements is a major limitation of solid-state dosimeters. This is especially true for PIN photodiode dosimeters, where the dark current depends exponentially on temperature. To minimize this effect, a compensation method is presented that relies on the diode structure itself without the need for an external sensor or device. During irradiation, the photodiode is periodically switched from reverse to forward polarization to determine the temperature of the device. This measurement is based on the linear dependence between the temperature and the forward voltage of the diode when it is operated at constant current. An electronic circuit implementing this procedure was developed and used for experimental characterization of the response to radiation of the BPW34S Si PIN photodiode. The proposed procedure reduced the uncertainty due to thermal drift by a factor of 7.5. In addition, an average dose rate sensitivity of 12 ± 2 nC/cGy was measured, with a sensitivity degradation below 2% for the irradiation cycle of 21.4 Gy performed under a 6 MV photon beam. We have shown that a p-n junction can be successfully used to compensate for the temperature effect on the dosimetric measurement. [ABSTRACT FROM AUTHOR]