An instrument for photoconductivity measurements in the presence of relatively large d-c currents

This instrument was developed as a solution to a problem which arose in our research on conductivity in rutile single crystals. In attempting to identify the origin of the charge carriers in the temperature range below 400°C, it was felt that photoresponse measurements would provide a clue. With illumination in the 1 micron region, a small transient photo current was observed with a d-c amplifier and recorder when the light was switched on. The peak amplitude of the transient was small, less than 10% of the dark current, and the decay time was that of the amplifier-recorder assembly.