Non-linear effects in doped-germanium photoconductors for the ISO long wavelength spectrometer

The ISO (Infrared Space Observatory) Long Wavelength Spectrometer (LWS) uses an array of ten doped Ge photoconductors to cover the wavelength range 45 to 200 micrometers. Under the low background conditions appropriate to the LWS, these devices are know to exhibit a number of memory effects, such as spontaneous spiking at high signal levels and slow relaxation after a step change in illumination. This type of nonlinear behavior can cause degradation of the excellent instantaneous sensitivity of the LWS detectors, and other calibration problems. These effects were studied and the implications of operation and calibration of the LWS are considered