Fabrication and structure modulation of high-aspect-ratio porous GaAs through anisotropic chemical etching, anodic etching, and anodic oxidation

The fabrication and modulation of hexagonally ordered arrays of deep pores in (1 1 1) GaAs were performed by combining colloidal crystal templating, anisotropic chemical etching, localized anodic etching and isotropic anodic oxidation. High-aspect-ratio triangular pore arrays of GaAs along the [1 1 1] crystallographic direction were induced by anodic etching in HCl through the apex of inverted triangular pyramid prepits, where electric field strength increased under anodic bias. The triangular pore arrays in GaAs changed to triangular pillar arrays during the anisotropic chemical etching. By applying anodic oxidation in a weak acid solution, the shape of pores in GaAs could be modulated from triangular to circular owing to the leveling effect, and a macroporous GaAs layer was formed. Four types of GaAs microstructure, that is, triangular pore arrays, prism-like pillar arrays, circular pore arrays and needle-like tip arrays, could be obtained by optimizing the chemical etching and anodization conditions.