Short-period SimGen (m monolayer (ML) Si, n ML Ge. n+m<∼40ML∼5.5nm) strained layer superlattices (SLS) are grown on <100> silicon by low temperature molecular beam epitaxy. Various characterization tools such as X-ray diffraction, transmission electron microscopy, Rutherford backscattering, Raman spectroscopy and photocapacitance measurements are used to analyze the growth quality, stram distribution, periodicity, interface sharpness and optical properties of the SLS. Recent photoluminescence experiments give hints of a direct bandgap transition from a 10 ML Si6Ge4 SLS in the near infrared spectral region. I-U and C-U measurements on mesa diodes (Am=2 10−4 cm2) are performed at various temperatures down to T=35K. Photocapacitance measurements show a Wannier-Stark localization of the superlattice states in a p+-n doped Si4Ge4 SLS diode, for the first time observed in type II superlattices. The observed transitions are believed to be defect or impurity related and are discussed in terms of a Wannier-Stark ladder behaviour.