SiGe quantum dot crystals with periods down to 35 nm

By combining extreme ultraviolet interference lithography with Si/Ge molecular beam epitaxy, densely packed quantum dot (QD) arrays with lateral periodicities down to 35 nm are realized. The QD arrays are featured by perfect alignment and remarkably narrow size distribution. Also, such small periodicities allow the creation of three-dimensional QD crystals by vertical stacking of Si/Ge layers using very thin Si spacer layers. Simulations show that the distances between adjacent QDs are small enough for coupling of the electron states in lateral as well as vertical directions.