Low Thermal Budget Fabrication of Local Artificial Substrates by Droplet Epitaxy on Silicon

The droplet epitaxy (DE) growth method for the fabrication of III-V material quantum nanostructures [1], is an intrinsically Low Thermal Budget technique, being fully performed at temperature between 200 and 350 °C. This makes DE perfectly suited for the realization of growth procedures compatible with back-end integration. In short, the DE growth procedure consists in the deposition at different times for the group III and group V elements. Group III elements create a regular pattern of liquid droplet on a substrate, group V elements are incorporated inside group III element crystalling the droplets into a quantum nanostructure. We can distinguish two main areas where fabrication of III-V quantum nanostructures on Si substrate could play a fundamental role. The first is the fabrication of nanostructured active layers at LTB with designed DOS for optimum device performance [2]. The second area concerns the realization of local artificial substrates for heterogeneous integration of quantum nanostructures [3]. The nucleation of quantum dots atop an island is an attractive approach to address radiative recombination issues and dot uniformity as the island both separates the dot from the interface with the substrate and provides a nucleation platform of sufficiently small dimension to realize quantum size effects. For this purpose we fabricated self-assembly of GaAs islands by DE which show highly tunable density (from 107 to 109 cm-2) and size (from 75 nm to 250 nm) and size dispersion below 10%. Changing the substrate temperature during the Ga deposition and the amount of irradiated Ga is possible to independently control the density and the size of the nanostructures (figure 1a). The islands, made by single relaxed crystals, show well defined shapes, with a high aspect ratio (Figure 1b). The low thermal budget required for the island self-assembly, together with the high scalability of the process, make these islands good candidates for local artificial substrates on Si. [1] N. Koguchi and K. Ishige, Japanese Journal Of Applied Physics 32, 2052-2058 (1993). [2] S.Bietti, C.Somaschini, S. Sanguinetti, N. Koguchi, G. Isella, and D. Chrastina, Applied Physics Letters 95, 241102 (2009). [3] C. Somaschini, S. Bietti, N. Koguchi, F. Montalenti, C. Frigeri, and S. Sanguinetti, Applied Physics Letters 97, 053101 (2010).