Nanometer-scale control of single quantum dot nucleation through focused ion-beam implantation

Abstract

In situ ${\mathrm{Ga}}^{+}$ focused ion-beam (FIB) implantation has been used to control the nucleation of individual Ge islands on the Si(001) surface at the nanometer scale. The patterning technique consists of three steps: (i) low dose implantation, (ii) post-implantation annealing, and (iii) ultrahigh vacuum deposition of Ge. Varying the conditions for the Ga implantation and the post-implantation anneal allows four types of surface features to be created, and features that present a particular nanotopography after annealing act as island nucleation centers. Furthermore, because of Ga surface segregation during post-implantation annealing, Ge islands formed on patterned substrates present different characteristics compared to conventional Ge islands grown on the unmodified Si(001) surface. We discuss the influence of growth parameters and pattern feature topography on island nucleation, and identify the ideal growth conditions that lead to the formation of one coherent island on each pattern feature and the tightest island size distribution. The patterning technique described here can presumably be applied to systems other than $\mathrm{Si}∕\mathrm{Ge}$ and to techniques other than FIB that allow the creation of suitable local nanotopography.