Ultra-low density InAs quantum dots

We show that InAs quantum dots (QDs) can be grown by molecular beam epitaxy (MBE) with an ultralow density of sin 10⁷ cm^?2 without any preliminary or post-growth surface treatment. The strain-induced QD formation proceeds via the standard Stranski-Krastanow mechanism, where the InAs coverage is decreased to 1.3–1.5 monolayers (MLs). By using off-cut GaAs (100) substrates, we facilitate the island nucleation in this subcritical coverage range without any growth interruption. The QD density dependences on the InAs coverage are studied by photoluminescence, atomic force microscopy, transmission electron microscopy, and are well reproduced by the universal double exponential shapes. This method enables the fabrication of InAs QDs with controllable density in the range 10⁷–10⁸ cm^?2, exhibiting bright photoluminescence.