Ordered Arrays of Vertically Aligned [110] Silicon Nanowires by Suppressing the Crystallographically Preferred Etching Directions

The metal-assisted etching direction of Si(110) substrates was found to be dependent upon the morphology of the deposited metal catalyst. The etching direction of a Si(110) substrate was found to be one of the two crystallographically preferred < 100 > directions in the case of isolated metal particles or a small area metal mesh with nanoholes. In contrast, the etching proceeded in the vertical [(1) over bar(1) over bar0] direction, when the lateral size of the catalytic metal mesh was sufficiently large. Therefore, the direction of etching and the resulting nanostructures obtained by metal-assisted etching can be easily controlled by an: appropriate choice of the morphology of the deposited metal catalyst. On the basis of this finding, a generic method was developed for the fabrication of wafer-scale vertically aligned arrays of epitaxial [110] Si nanowires on a Si(110) substrate. The method utilized a thin metal film with an extended array of pores as an etching catalyst based on an ultrathin porous anodic alumina mask, while a prepatterning of the substrate prior to the metal depostion is not necessary. The diameter of Si nanowires can be easily controlled by-a combination of the pore diameter of the porous alumina film and varying the thickness of the deposited metal film.