Abstract: Pseudomorphic Si_1-xGe_x layers are grown in GSMBE system using gas source disilane and elemental germanium. This source combination is expected to have advantages of the surfactant effect by the use of disilane and the abrupt ON/OFF capability of germanium flux by the use of elemental germanium. Double crystal X-ray diffraction, transmission electron microscopy and photoluminescence measurements were used to determine the germanium composition, crystalline quality and interface flatness. Results indicate that high quality Si_1-xGe_x/Si heterostructures can be grown with elemental Ge instead of gas source Ge in the GSMBE system.