We have studied the influence of nanoscaled lateral silicon/silicon-germanium layers and three-dimensional germanium quantum dots on the performance of silicon based infrared detectors in the wavelength range between 2 and 10 tm and solar cells for space applications. The SiGe heterostructures were grown by molecular-beam epitaxy (MBE) on (100)-Si substrates allowing it to tailor the photoresponse and cut-off wavelength for IR-detectors by "band engineering" of the Ge-content and geometry of the active layers. A detectivity in excess of 8 x 10(11) cmHz(0.5)/W at 75 K was measured for Si/SiGe quantum well structures. In addition, the growth of Ge islands on Si layers in the Stranski-Krastanow mode was performed to increase absorption and quantum efficiency in Si-solar cells. Atomic force microscopy and photoluminescence measurements of Ge-island structures, grown by MBE under varying conditions, exhibit three-dimensional growth in a small temperature regime between 500 degreesC and 700 degreesC.