Nano patterns self-aligned to Ga dimer rows on GaAs surfaces

TL;DR

This paper demonstrates that ion beam irradiation creates self-aligned nanoscale ripples on GaAs surfaces by revealing their alignment to Ga dimer rows, advancing understanding of pattern formation in semiconductor nanostructures.

Contribution

It uncovers the origin of ripple self-alignment on GaAs surfaces, linking it to Ga dimer rows through experimental exposure of front and back sides.

Findings

Ripples align with Ga dimer rows on GaAs surfaces.

Orientation of ripples changes with dimer row direction.

Pattern formation driven by vacancy and ad-atom diffusion.

Abstract

Ion beam irradiation of semiconductors is a method to produce regular periodic nanoscale patterns self-organized on wafer scale. At low temperatures, the surface of semiconductors is typically amorphized by the ion beam. Above a material dependent dynamic recrystallization temperature however, the surface remains crystalline and ion beam irradiation produces regular arrays of faceted ripples on III-V semiconductors. This provides a powerful single-step technique for the production of nanostructures on a large area. On $(001)$ surfaces these ripples are parallel to the $[1\bar{1}0]$ direction without any external anisotropy. The origin of this self-alignment was not fully understood until now. A simple experiment exposing the front side and back side of a GaAs$(001)$ wafer to the ion beam clarifies its origin and proves that the ripples align to the Ga dimer rows. As the direction of Ga dimer rows rotates by 90{\deg} on the back side, the orientation of the ripples also rotates by 90{\deg} to $[110]$. We discuss the experimental results in view of a model where the pattern formation is driven by creation of vacancies and ad-atoms by the ion beam and their diffusion, which is linked to the direction of dimers on the surface.