Nanopatterning during ion sputtering: The reverse epitaxy mechanism on crystalline surfaces


Nanopatterning during ion sputtering: The reverse epitaxy mechanism on crystalline surfaces

Erb, D.; Malsch, G.; Engler, M.; Ou, X.; Facsko, S.

Normal-incidence low energy ion irradiation is known to amorphize and smoothen semiconductor surfaces via ballistic redistribution of atoms by the impacting ions [1]. However, intriguing nanoscale surface patterns can form spontaneously, if the semiconductor substrate is heated above its recrystallization temperature during ion irradiation [2].

Above the recrystallization temperature the surface remains crystalline even under ion irradiation: On the one hand, bulk defects are annealed instantly. On the other hand, on a crystalline surface the diffusing surface vacancies and ad-atoms encounter the Ehrlich-Schwoebel barrier, the energy barrier for crossing terrace steps. In analogy to epitaxial growth, this can lead to the formation of well-defined faceted surface structures for ion irradiations performed in a specific energy and temperature range [2]. The resulting surface morphology is strongly dependent on the crystalline structure and surface orientation of the semiconductor substrate. For instance, Ge(001) exhibits inverse pyramids with a square base and Ge(111) shows inverse pyramids with a threefold symmetry, while GaAs(001) and InAs(001) develop regular ripple structures with a saw tooth profile [3]. The periodicity and the regularity of the surface pattern can be influenced by external process parameters such as substrate temperature, ion energy, and ion fluence.

In this contribution, we outline the reverse epitaxy mechanism, highlight the diversity of resulting surface patterns, and present possible applications, for instance in templated metal nanostructure growth or in the fabrication of semiconductor nanostructures.

[1] C S Madi et al., Physical Review Letters 106, 066101 (2011)
[2] X Ou et al., Physical Review Letters 111, 016101 (2013)
[3] X Ou et al., Nanoscale 7, 18928 (2015)

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