Small Ordered Ge Quantum Dots Growth on Si (100) Hollow Nanopillars.

The application of ordered Ge quantum dots (QDs) is limited by the indirect bandgap and the large size. Here, a structure of hollow nanopillars (HNPs) is proposed to grow small ordered Ge QDs using molecular beam epitaxy by suppressing the expansion of the central holes (CHs) during degassing and inhibiting the lateral growth of Ge QDs, the growth mechanisms are explained by the evolution of surface morphology and the surface chemical potential distribution. The width of Ge QDs in CHs mainly depends on the diameter of HNPs and has little relationship to the diameter of CHs. The small ordered Ge QDs with a mean base diameter of 47.1 nm and a period of 1 μm are grown under high growth temperature (580 °C). The size, shape, height, and period of HNPs are all shown to affect the growth of Ge QDs in CHs. Hence, HNPs provide us with more controllable parameters than pits to control the shape, location, and size of Ge QDs.