We have studied optical spectra in p-type Si/SiGe heterostructures designed for applications in the range of 1-20 mu m wavelengths. Our results have been obtained in full-scale microscopic calculations and we present optimized device structures for thermal imaging devices. We also studied in detail the effects of substrate and barrier doping on the Fermi level and the resultant thermal offsets, an important parameter for determining the magnitude of the dark current in any device. Auger rates are presented for band-to-band and intra-valence band processes and compared with data for bulk materials.