GaAs based nanostructures grown by droplet epitaxy

What makes three dimensional semiconductor quantum nanostructures (QN) so attractive is the possibility to tune their electronic properties by careful design of their size and composition. These parameters set the confinement potential of electrons and holes, thus determining the electronic and optical properties of the QN. An often overlooked parameter, which has a even more relevant effect on the electronic properties of the QN, is shape. Gaining a strong control over the electronic properties of semiconductor nanostructure via shape tuning is the key to access electronic fine design possibilities. We present an innovative growth method, the Dropled Epitaxy (DE) [1,2], a variant of molecular beam epitaxy, for the fabrication of semiconductor III-V QNs with highly designable shapes and complex morphologies. In short, the DE growth procedure consists of first irradiating the substrate with a group III molecular beam flux, leading to the formation of numerous, nanometer-sized, metallic droplets on the surface which are subsequently crystallized into nanostructures by a group V molecular beam. With DE is possible to combine multiple single QNs, namely quantum dots, quantum rings and quantum disks, with tunable sizes and densities, into a single multi-functional QN thus allowing an unprecedented control over the electronic properties of the QNs [2,3] (see Figure 1). In addition, DE is intrinsically a low thermal budget growth of III-V materials, being fully performed at 200- 350°C. This makes DE perfectly suited for the realization of growth procedures compatible with back- end integration of III-V materials on Si [4,5]. [1] N. Koguchi, et al., J. Cryst. Growth (1991), 111, 688 [2] C. Somaschini, et al., Nano Letters 2009, 9, 3419 [3] C. Somaschini, et al., Nanotechnology 2010, 21, 125601 [4] S. Bietti, et al., Appl. Phys. Lett. 2009, 95, 241102 [5] C. Somaschini, et al. Appl. Phys. Lett. 2010, 97, 053101