Semiconductor device fabrication method and structures are provided having a substrate structure which includes a silicon layer at an upper portion. The silicon layer is recessed in a first region of the substrate structure and remains unrecessed in a second region of the substrate structure. A protective layer having a first germanium concentration is formed above the recessed silicon layer in the first region, which extends along a sidewall of the unrecessed silicon layer of the second region. A semiconductor layer having a second germanium concentration is disposed above the protective layer in the first region of the substrate structure, where the first germanium concentration of the protective layer inhibits lateral diffusion of the second germanium concentration from the semiconductor layer in the first region into the unrecessed silicon layer in the second region of the substrate structure.