Long-term performance of doped Ge:Ga photoconductors in the space environment

The long wavelength spectrometer on board the ESA IR Space Observatory employs doped geranium photoconductors to perform spectroscopy in the 43 to 197 micrometers waveband. The instrument has been in continuous on orbit operation for over two years - longer than any other experiment in this waveband. Invaluable data have been gathered on the long term performance of a beryllium doped germanium detector and both stressed and unstressed gallium doped germanium detectors in the presence of ionizing radiation in the form of cosmic rays and charged particles trapped in the Earth's magnetic fields. In this paper we report on the in-orbit performance of the detectors and in particular on the long term behavior of the dark current and responsivity.