4x32 FIRGA array: a pacesetter for a 52x32-element gallium arsenide focal plane array

Abstract

FIRST and SOFIA are both future infrared observatories with 3m class main mirrors having sophisticated instrumentation aboard. The present design of the FIRST imaging spectrometer PACS requires two large far-infrared photoconductor arrays of 25x16 pixels each, the baseline material is stressed and unstressed Ge:Ga. A gallium arsenide photoconductive detector which is sensitive in the far infrared (FIR) wavelength range from about 60 .tm to 300 m might offer the advantage of extending considerably the long wavelength cut-off of presently available photodetectors. FIRGA is an ESA sponsored detector development program on this matter involving international partners. The aim is a monolithic 4x32 demonstrator array module with associated cryogenic read-out electronics. Recent progress in material research has led to the production of Te-doped n-type GaAs layers using liquid phase epitaxy (LPE). We prepared sample detectors from those materials and investigated their electrical and infrared characteristics. First measurements indicate that GaAs has in principle considerable potential as a FIR photon detector. Theoretical modeling of GaAs detectors (bulk type and blocked impurity conduction band devices) can help with the detector design and allows the prediction of response transients as a function of detector parameters. Present development activities are mainly concentrating on material research, i.e. the production of GaAs:Te with improved FIR characteristics. Results of the current tests and measurements are reported. The FIRGA study is intended to prepare the technology for large two dimensional GaAs detector arrays for far infrared astronomy.

GaAs:Se and GaAs:Te Photoconductive Detectors in 300 µm Region for Astronomical Observations

“…Katterloher and coworkers developed an LPE-grown GaAs photoconductor doped with tellurium (GaAs:Te) in order to make accurate astronomical observations. [10][11][12][13][14][15] However, this photoconductor has not yet been used for making actual observations. Cardozo et al attempted to fabricate the blocked-impurity-band (BIB) structure of a GaAs:Te photoconductor, and they investigated the far-infrared absorption coefficient of the Te donors in GaAs.…”