Development of GaAs photoconductors for far-infrared/submillimeter astronomy

In today's Astronomy, there is little observational results in the spectral window ranging from far-infrared to submillimeter wavelength. As one of the main reason of this, there is no high performance detector in this spectral region. We started the development of the extrinsic photoconductor for this region utlizing shallow donor levels of gallium arsenide (GaAs) as a host material. GaAs is a good candidate as the material of the photoconductor, according to its small effective mass of conduction electrons, which leads to high performance of the detector. We began this development from the crystal growth of GaAs wafer using the liquid phase epitaxy (LPE). Using this method, we have grown about 60 samples of GaAs epitaxial wafer, and several of these samples showed very low-carrier concentration, which is suitable for the detector. And we also fabricated a proto-type detector from LPE grown GaAs wafer, and measured its response for far-infrared photons with several different conditions. The photons of the wavelength ranging between 100 and 300 micron were detected by the detector, and it was observed the highest efficiency of detection of about 0.07.