Nonbolometric NbN photodetector

There have been several recent reports of apparently nonbolometric optical responses in superconducting thin films. The photoresponse of 10 nm thin superconducting NbN meander lines on Si is measured at 670 nm using a diode laser modulated to more than 100 kHz. Several types of photoresponse are identified, some apparently due to the Si substrate. A fast photoresponse due to the NbN film with a responsivity of up to 125 V/W of absorbed power was observed. Results are analyzed in the context of a bolometric model, and the magnitude of the photoresponse is found to be too large for a purely bolometric response. Possible nonbolometric alternatives are discussed.<>