GaAs BIB photodetector development for far-infrared astronomy

Abstract

GaAs photoconductive detectors offer an extended spectral response in the far-infrared (FIR) compared to presently available stressed Ge photoconductors. Furthermore, responsivity at wavelengths up to 330 microns can be reached without having to apply uniaxial stress close to the breaking limit on each pixel. This would greatly simplify the production of detector arrays and therefore allow much larger numbers of pixels. Such arrays are highly demanded for upcoming far-infrared astronomy missions with space and airborne telescopes. However, bulk GaAs photoconductors have only limited sensitivity, due to low absorption and high dark currents. Considerable improvement of the detector performance can be expected from the development of GaAs blocked impurity band (BIB) devices. Our recent crystal growth experiments show that the liquid phase epitaxial (LPE) technique is capable of producing the required purity for the blocking layer. We have also performed far-infrared absorption measurements of doped GaAs layers which demonstrate the spectral range extension to about 330 microns and the enlarged absorption coefficient for the more highly doped absorption layer. Experimental work is supported by numerical modeling of BIB devices done in our group.