Molecular beam epitaxy (MBE) is a powerful technique used to grow semiconductor crystalline Jayers at low (200°C - 900 °C) temperature. In this study we report on the growth of silicon-based materials used for their electronic and optical properties. Parts of the work have involved alloys of silicon (Si) with germanium (Ge) or carbon (C). One possibility to have infrared light emission from silicon-based material is to use doping with the rare-earth erbium ions (Er3+) combined with oxygen (O), and the incorporation behaviors of these atoms were studied for two different doping source combinations. The influence on the crystalline quality of the doping concentrations and the substrate temperature were extensively investigated and e.g. it has been shown that very high concentrations of Er (1x1020 cm-3) and O (5x1020 cm-3) can be incorporated at 430°C into a Si crystal without extended defects. The material properties were principally characterized by electroluminescence (EL), and cross-sectional transmission electron microscopy (XTEM).