MBE growth and properties of branched AlGaAs nanowires on silicon

Branched III-V nanowires (NWs) are interesting both from the fundamental viewpoint and for the development of electronic and optoelectronic structures with enhanced functionality. Herein, we present a robust approach to synthesis of branched AlGaAs NWs using the Au-catalyzed molecular-beam epitaxy directly on Si(111) substrates. The second and third deposition of Au onto the substrate with NWs gives rise to the first and second generation of branches. First generation branches grow in the [1-100] direction perpendicular to the NW trunks; their coalescence yields the NW bridging. Compositional and structural analysis, performed by transmission electron microscopy and Raman spectroscopy, reveal an AlAs fraction of 0.2-0.3 and almost pure wurtzite crystal phase of both NW trunks and uncoalesced branches of the first generation. According to the microscopy measurements the wurzite phase purity is more than 95%. The method is useful for obtaining complex branched structures in wurtzite AlGaAs NWs on Si substrates, and may be translated to other material systems. These branched structures open new perspectives for next generation optoelectronic, energy harvesting and biological devices.