Long-wavelength Ge x Si 1-x /Si heterojunction infrared detectors and focal-plane arrays

Abstract

Heterojunction GexSi1-x/Si internal-photoemission infrared detectors exhibiting nearly ideal thermionic-emission dark-current characteristics have been fabricated with cutoff wavelengths out to 25 micrometers . Heteroepitaxial p-GexSi1-x layers, degenerately doped with boron to concentrations exceeding 1020 cm-3 in order to obtain high free-carrier absorption, are grown in Si substrates by molecular beam epitaxy. The detector cutoff wavelength, which is determined to first order by the valence- band offset, is tailored by varying the composition of the GexSi1-x layer and can be fine tuned by adjusting such parameters as the doping concentration and growth temperature. High-quality imaging without uniformity correction has been demonstrated in the long-wavelength infrared spectral band for 400 X 400- and 320 X 244-element focal plane arrays consisting of GexSi1-x/Si detectors, which have cutoff wavelengths of 9.3 and 10.5 micrometers , respectively, and monolithic CCD readout circuitry.