Reverse Epitaxy on Elemental Semiconductors

1. INTRODUCTION
Self-organized pattern formation during ion beam erosion can produce a variety of periodic patterns. Depending on the substrate and the irradiation conditions ripples, dots, holes or checkerboard patterns have been observed [1]. Pattern formation by low energy ion beam irradiation at low temperature, where the semiconductor surface is amorphized has been studied in detail in the last decades.

Low energy ion beam irradiation performed above the dynamic recrystallization temperature prevents the amorphization of the semiconductor surface. Above this transition temperature, the diffusion of adatoms and vacancies across step edges is hindered by an additional potential barrier, the Ehrlich-Schwoebel barrier. This barrier induces an effective destabilizing surface current during ion beam irradiation. This instability induces pattern formation even at conditions leading to a smooth surface below the transition temperature.

This mechanism, termed reverse epitaxy [2], allows the creation of novel types of surface patterns aligned to certain crystallographic directions of the irradiated surface.

2. PATTERNS FORMED
In this contribution we will present different types of patterns on elemental semiconductor surfaces and how it can be changeds by choosing the surface orientation and the irradiation conditions. For example, the pattern changes qualitatively on Si(100) under 2 keV Kr ion irradiation (Figures 1 and 2) with the ion fluence. Furthermore the pattern symmetry is determined by the symmetry of the irradiated surface. For Si(100) the ridges in the high fluence case are aligned to the [010] and [001] directions, whereas on Si(110) (Figure 3) the pattern is symmetric to the [110] and [001] directions.

3. REFERENCES
[1] Chan, Wai Lun, and Eric Chason. J. Appl. Phys. 101 (2007): 121301
[2] Ou, Xin, Adrian Keller, Manfred Helm, Jürgen Fassbender, and Stefan Facsko. Phys. Rev. Lett. 111 (2013): 016101