Lithography-free positioned GaAs nanowire growth with focused ion beam implantation of Ga

The authors report on a technique to grow GaAs nanowires at defined positions by molecular beam epitaxy without the need for a lithographic process. Here, a focused ion beam is used to implant Ga ions into Si (1 0 0) and Si (1 1 1) substrates, forming nanoscale droplets on the surface after an annealing step, which are in turn used as nucleation centers for self-catalyzed nanowire growth. This procedure completely avoids organic chemicals, as needed in other lithographic processes, and therefore allows nanowire growth in defined and flexible geometries, while being fully compatible with ultraclean environments. A minimum required pitch width is determined from implanted Ga point arrays, which were annealed to form droplets. The epitaxial yield for GaAs nanowires on Si (1 0 0) and Si (1 1 1) substrates is evaluated with respect to the acceleration voltage and implanted dose. The nanowire diameter is determined by thermodynamic properties at the growth surface while being insensitive to implantation parameters.