Development of a far-infrared detector array for FIRST based on n-type ultrapure liquid phase epitaxial gallium arsenide

Abstract

We consider a 16 X 16 pixel GaAs photoconductive detector array as a new candidate for an ESA-sponsored detector development program. A photoconductor array covering the wavelength range from 150 to 300 microns can add to the capability of the far infrared imaging spectrometer in the model payload of FIRST (far infra-red and submillimeter space telescope). The GaAs detector array is a completely new development. The spectral response of GaAs has been known for years; gallium arsenide, however, was at that time not available in a quality to bring dark current and NEP at operating temperatures around 1 K down to levels of state of the art photoconductors. Recent progress in liquid phase epitaxy led to the production of very high purity GaAs. Contamination from the growth system can now be kept below the required donor concentration leading to n-type GaAs layers. Photoluminescence spectra indicate low compensation, a vital requirement for getting effective photoconductive detectors. Layers with a thickness of a few hundred microns were recently produced. The GaAs detector is likely to become available within the next few years. The paper discusses investigations of the material and first results of sampling detector development.