Sub-critical InAs layers on metamorphic InGaAs for single quantum dot emission at telecom wavelengths

We report on the design, the growth by MBE and the optical and morphological characterization of metamorphic InAs/InGaAs quantum dots (QD) with a density low enough to allow single dot characterization without the need of complex litographic steps to isolate single QDs. InAs sub-critical coverages were deposited on InxGa1-xAs metamorphic buffers (MBs) and the transition from 2D growth to 3D island nucleation was monitored by reflection high energy electron diffraction (RHEED). We discuss the fundamental differences of the sub-critical growth method compared with the Stranski-Krastanow one, also by considering available theoretical models. AFM confirmed that the density of QDs can be controlled down to 10(8) cm(-2) and showed that InGaAs surfaces have an effect on QD positioning uniformity. Optical properties were studied by ensemble PL at 10 K and by mu-PL at 4 K and single dot emission was detected in the whole range from 1000 to 1315 nm for structures grown on In0.15Ga0.85As MBs, allowing to identify most of the excitonic species at the ground state. In conclusion, our results show that the sub-critical QD growth technique can be successfully used to prepare low-density InAs QD structures on InxGa1-xAs (x >= 0.15) metamorphic buffers and that, based on advanced mu PL characterization, these nanostructures can be effective single photon sources emitting at 1300 nm, with the potential of emission extension towards 1550 nm.