Embodiments of the present invention describe a semiconductor device having an buffer structure and methods of fabricating the buffer structure. The buffer structure is formed between a substrate and a quantum well layer to prevent defects in the substrate and quantum well layer due to lattice mismatch. The buffer structure comprises a first buffer layer formed on the substrate, a plurality of blocking members formed on the first buffer layer, and second buffer formed on the plurality of blocking members. The plurality of blocking members prevent the second buffer layer from being deposited directly onto the entire first buffer layer so as to minimize lattice mismatch and prevent defects in the first and second buffer layers.