Photoconductive Devices (PC) are detectors based on the photoconductive effect. Infrared radiation generates charge carriers in the semiconductor active region decreasing its resistance. The resistance change is sensed as a voltage change by applying a constant current bias. The optimum bias current is specified in the Final Test Report and depends on the detector size, operating temperature and spectral characteristics. The PC detectors we offer comes with different spectral response.
Source (with permission to reproduce): https://vigo.com.pl/en/support/faq/