TRANSIENT-RESPONSE IN DOPED GERMANIUM PHOTOCONDUCTORS UNDER VERY-LOW BACKGROUND OPERATION

Doped germanium photoconductors are the most sensitive detectors for a stronomy in the wavelength range 40-240 mu m. Under the extremely low background conditions encountered in cooled satellite instruments, the se devices exhibit a number of transient effects, such as slow relaxat ion after a step change in illumination or bias, and spontaneous spiki ng at high signal levels. Such behavior can degrade the excellent inst antaneous sensitivity of these detectors and create calibration uncert ainties. These effects have been observed in the Ge:Be photoconductors and the stressed and unstressed Ge:Ga photoconductors in the Long Wav elength Spectrometer, one of the instruments on the Infrared Space Obs ervatory. A systematic investigation of the transient response of the Long Wavelength Spectrometer detectors to a step change in illuminatio n as a function of operating temperature, bias electric field, and ill umination step size has been carried out to determine operating condit ions that minimize the effects of this behavior. The transient effects appear to be due primarily to carrier sweep out, but they are not ful ly explained by existing models for transient response. (C) 1996 Optic al Society of America.