AUTOMATED ABSOLUTE AND RELATIVE SPECTRAL LINEARITY MEASUREMENTS ON PHOTOVOLTAIC DETECTORS

The paper discusses automated spectral linearity measurements using both absolute and relative methods. Results of measurements on typical silicon and germanium photodiodes are presented. These measurements show the agreement between the two methods. They also illustrate some interesting linearity properties: wavelength dependence, detector-to-detector variation, current versus current-density dependence, geometrical effects, and effect of reverse bias. In particular, it is shown that some silicon and germanium detectors must be underfilled with radiation to avoid edge effects. These cause nonlinearities which are generally small (1 % level) but, in certain types of thermoelectrically cooled germanium detectors, can be very large (8 % to 10 %).