We present full-scale calculations of highly p-type doped SiGe heterojunction internal photoemission (HIP) detectors that operate in the mid-infrared (3- to 5-μm) range of wavelength. We explore the effects of including undoped spacer layers within the highly doped SiGe wells, for which a systematic body of experimental data is available to us, and which demonstrates a substantial reduction in the dark current produced by these devices. We model the doping explicitly by means of a screened Coulomb potential, leading to a full description of the resultant impurity band, and compare our calculated optical line shapes with recent state-of-the-art molecular-beam epitaxy experiments. The variation of the optical response with well width, germanium concentration, spacer width and position, and doping concentration are all considered.
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