A detector in which the voltage changes in response to incident radiation. In a simple p–n semiconductor junction, incident radiation leads to a flow of current over the junction, and the device acts as a photoconductive detector. But if the diode is in series with a very high resistance, the voltage across that resistance changes with the intensity of the incoming radiation, so that the diode then acts as a photovoltaic detector. Various semiconductor materials such as silicon, indium antimonide, and gallium arsenide can be used for the detectors. They can operate from visual wavelengths to 10 μ‎m or longer.