Highly p-doped silicon/silicon-Germanium (SiGe) quantum well structures have been grown by molecular beam epitaxy on [100] Si substrates as detectors in the midinfrared regime (3-5 mu m; 8-12 mu m). These detectors-operating from about 3 to 20 mu m-are based on heterointernal photoemission of photogenerated holes across the Si/SiGe valence band from a highly p-doped SiGe layer which is grown on an undoped (50 Omega cm), double-sided polished Si substrate. The thickness of the well, its doping level, and its Ge content determines the valence band offset and thus the operating wavelength of the detector. This layer sequence has been repeated up to five times and the structure has been terminated with a p-doped SiGe contact layer on top. The samples grown have been extensively analyzed by secondary ion mass spectroscopy, x-ray diffraction, Rutherford Backscattering, and absorption spectroscopy. Mesa detectors of varying diameters have been fabricated using a standard Si processing technique, and the photocurrent and dark current have been measured at 77 K. A broad quantum efficiency of eta(ext)=0.3% has been obtained (at 4 mu m and 77 K) with dark current densities as low as 10(-8) A/cm(2). The photoresponse spectrum shows a broad maximum between 3 and 5 mu m; it is shown that the peak in this spectrum can be tuned over a fairly broad range by the choice of layer composition.