Optimal growth of Ge-rich dots on Si(001) substrates with hexagonal packed pit patterns

This paper reports a three-step method to fabricate hexagonal ordered Ge dots on Si with controllable size and spacing. After the introduction of a thin Si dioxide layer on the Si substrate, porous alumina turns out to be a good candidate for pattern transferring, which is rapid and simple to implement. A density-temperature relation for Ge dots has been discovered in this work; the Arrhenius relation with a slope of 0.33 is proved to be applicable for predicting the optimal temperature for a certain density of patterns. Different widths of pits are also studied to discover the dependence of the dot distribution on the pit morphology. The optimal pit width for ordered Ge dots is around 30 nm, while four aligned Ge dots can be achieved in a 70 nm pit. Extremely high Ge content (>0.92) in capped Ge dots is discovered by Raman characterization because the high density of pits leads to a low enough optimal temperature of 430 °C. The photoluminescence spectra of the capped dots also prove the high purity and quality of the Ge dots.