Precision placement of heteroepitaxial semiconductor quantum dots

We describe two new approaches to the patterning of Si(1 0 0) surfaces for controlled nucleation of heteroepitaxial Ge semiconductor clusters. In the first method, a Ga+-focused ion beam in situ to the growth chamber is used to create local regions of enhanced Ga+ concentration and surface topography. It is shown that at low ion doses (∼1014 cm−2), implanted Ga causes local nucleation of Ge clusters upon the implanted region. At higher doses (≥1015 cm−2), a complex surface topography localizes nucleation of Ge clusters. This approach can be used to seed complex patterns of Ge clusters with diameters of tens of nanometers and positional accuracy of sub-100 nm. The second method employs self-assembly of complex strain-stabilized “quantum quadruplet” and “quantum fortress” structures, whereby cooperative island nucleation around shallow strain-relieving pits is identified during GexSi1−x/Si(1 0 0) heteroepitaxy. These configurations are kinetically limited structures that exist over a range of compositions, growth temperatures, and growth rates, but which are destabilized by strain relaxation (e.g. by the introduction of misfit dislocations) and by growth conditions which provide high adatom surface mobilities. Both methods have broad potential application to nanoelectronic device architectures.