Methods for formation of epitaxial layers containing silicon are disclosed. Specific embodiments pertain to the formation and treatment of epitaxial layers in semiconductor devices, for example, Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices. In specific embodiments, the formation of the epitaxial layer involves exposing a substrate in a process chamber to deposition gases including two or more silicon source such as silane and a higher order silane. Embodiments include flowing dopant source such as a phosphorus dopant, during formation of the epitaxial layer, and continuing the deposition with the silicon source gas without the phosphorus dopant.