Droplet Epitaxial Nano-structures as Single Photon Sources on Silicon

Droplet epitaxy (DE) is a non-conventional growth technique based on molecular beam epitaxy. This method, differently from strain-induced 3-dimensional nano-structures, enables the growth of lattice-matched and strain-free self-assembled III-V nano-emitters. Thanks to the versatility of the DE, different kinds of nano-structures can be implemented: quantum dots, coupled quantum dots, multiple concentric quantum rings, quantum disks, as well as combinations of these different shapes can be obtained by playing with the growth conditions. Moreover, DE enables the growth on different substrates orientations (such as the (100), (311)A, (111)A) enabling ultra-low or ultra-high nano-structure density. Most importantly, DE makes possible the growth of bright III-V quantum emitters on substrates made of Silicon and Germanium. In this talk I will introduce some features of growth and photoluminescence spectroscopy of single GaAs/AlGaAs DE nano-structures. In particular I will concentrate on quantum dots and rings addressing their electronic structure, fine structure and line broadening: I will show how the composition, shape, geometrical anisotropy and disorder rule the optical properties and how, thanks to recent advances in the DE method, bright and sharp photoluminescence lines can be obtained in circular symmetric quantum dots. Finally, I will show recent advances in the growth of III-V nano-structures on IV-IV substrates demonstrating single photon emission at high temperature fully compatible with CMOS silicon devices.