Shallow acceptors in strained multiquantum-well Ge/Ge1-xSix heterostructures

Far infrared photoconductivity spectra due to excitation of shallow acceptors in strained multiquantum well Ge/Ge1-xSix (x approximate to 0.1) heterostuctures are investigated. It is shown that these spectra are shifted toward longer wavelengths in the far infrared region compared with those of bulk p-Ge, owing to "built-in" strain and size quantization, which lead to splitting of the light- and heavy-hole subbands in the Ge layers. Shallow acceptor spectra are calculated variationally for bulk germanium under uniaxial tension, which is "equivalent" to the strained Ge layers in the heterostructures. Although this method is only appropriate for wide quantum wells (d(Ge) approximate to 800 Angstrom), the calculations are shown to qualitatively account for photoconductivity spectra obtained from narrower wells (d(Ge) approximate to 200 Angstrom) as well. (C) 1998 American Institute of Physics. [S1063-7826(98)02010-9].