Two-dimensional periodic alignment of self-assembled Ge islands on patterned Si(001) surfaces

Two-dimensional alignment of Ge islands is obtained by molecular beam epitaxy of Ge on lithographically patterned Si(001) surfaces composed of periodic arrays of square Si mesas. When the period of the Si mesa arrays is reduced to 140 nm, a “one island on one mesa” relationship is achieved. The Ge islands have an average base width of 85 nm and take on the shape of a truncated pyramid with four {114} facets and a (001) top. The patterning also serves to improve the island size uniformity. The dependencies of the island morphology on the sizes of the Si mesas and Ge coverages are examined to clarify the mechanism of preferential nucleation of Ge islands on the tops of Si mesas.