An important consequence of this relatively low absorption coefficient 1986), which gives an absorption coefficient of 2 cm -1. Impurity banding effects that cause a huge increase in the dark current. In practice the concentration is limited by the onset of In principle, it is desirable to make n as high as possible. Is given by the product of the photoionization cross section s( l)Īnd the doping concentration of the impurity n. Ge:Sb detectors have a cutoff wavelength of 130Ĭoefficient of an extrinsic photoconductor at wavelength l The other dopant that has had significant application in infrared astronomy has been antimony. Used in the SIRTF focal plane arrays is shown in The spectral response for the Ge:Ga detectors Germanium (Ge:Ga) detectors have cutoff a Historically, the most important of these impurities in germanium hasīeen the p-type dopant gallium. With elements that have shallow extrinsic levels. Longer wavelength response is possible if the semiconductor is doped
Gaps of silicon and germanium are 1.11 and 0.67 eV, respectively,Ĭorresponding to long wavelength cutoffs of 1.1 mmĪnd 1.8 mm. IRAS produced these remarkable results utilizing only 16 discrete detectors Images that were produced by the IRAS mission. The most comprehensive look at the far-infrared sky. In particular, the survey of IRAS used Ge:Ga photoconductors to produce Will be used on the future missions SIRTF, IRIS and FIRST. Wavelength Spectrometer, Long Wavelength Spectrometer, and ISOPHOT), and they
#Solvent cut off wavelength iso
Including IRAS, Spacelab-II Infrared Telescope, IRTS, COBE, and ISO (Short These detectors have been used on all the far-infrared space missions The detector of choice has been the germanium photoconductor. The use of bolometers in space-borne applications has been very limited.
As thermal detectors, however, bolometers are limited by the phononįluctuations in the device, and state-of-the-art performance requires Groups around the world have produced highly sensitive arrays of bolometers. Progress has been made in recent years on bolometer technology, and several BolometersĪre thermal detectors that sense the temperature change caused by theĪbsorption of far-infrared photons. The two most widely used detectors at these wavelengths have been bolometersĪnd germanium photoconductors. Silicon-based detectors do not function, and alternate technologies are Luminous infrared galaxies, protostars, and debris disksĪround stars all have peak emissions at far-infrared wavelengths. Part of the spectrum is crucial for the study of many astrophysically Future directions are discussed, including concepts for large formatĪrrays, modifications for high background operation, and blocked impurity band In modeling of the non-linear behavior of the detectors is presented. Of recent focal plane array designs, in particular the detectors for the SIRTF This paper describes the operational theory of these detectors, The bulk of our knowledge of the far-infrared properties ofĪstronomical objects has come from observations made with these detectors. Photoconductors have been used in a variety of infrared astronomicalĮxperiments, both airborne and space-based.