Examples of the present technology include semiconductor processing methods to form diffusion barriers for germanium in a semiconductor structure. The methods may include forming a semiconductor layer stack from pairs of Si-and-SiGe layers. The Si-and-SiGe layer pairs may be formed by forming a silicon layer, and then forming the germanium barrier layer of the silicon layer. In some embodiments, the germanium-barrier layer may be less than or about 20 Å. A silicon-germanium layer may be formed on the germanium-barrier layer to complete the formation of the Si-and-SiGe layer pair. In some embodiments, the silicon layer may be an amorphous silicon layer, and the SiGe layer may be characterized by greater than or about 5 atom % germanium. Examples of the present technology also include semiconductor structures that include a silicon-germanium layer, a germanium-barrier layer, and a silicon layer.