Novel nano-scale site-controlled InAs quantum dot assisted by scanning tunneling microscope probe

We propose a novel site-control technique for strained quantum dots (QDs) based on nano-lithography using an STM integrated into a UHV STM/MBE multi-chamber system. A nano-scale deposit was formed on a GaAs surface by biasing between the GaAs surface and the tungsten tip of the STM. Because the deposit acted as a nano-mask, the subsequent GaAs growth formed a nano-hole just above the deposit. Subsequent InAs supply produced a QD on the hole site, and no QD was observed in off-site regions. We discuss the physical processes involved in the technique, based on step-by-step STM observations of the QD formation process. A 100 nm-pitch array of paired 45 nm-pitch QDs was also successfully formed. This shows that the technique can be used to form a QD at any required position with nm-level precision, thus achieving the artificial nm-scale arrangement of each QD.