Self-Organized Surface Structures on Compound Semiconductors by Polyatomic Ion Irradiation

Irradiation of solids by heavy polyatomic ions of gold or bismuth can cause localized melting at the ion impact point due to the enhanced energy density in the collision cascade of a polyatomic ion impact [1]. Former studies demonstrated the formation of high aspect ratio, hexagonal dot patterns on Ge, Si and GaAs after high fluence, normal incidence irradiation choosing a suited combination of energy density deposition (i.e. poly- or monatomic ions) and substrate temperature, which facilitated transient melting of the ion collision cascade volume [2-5].
This study underscores the universality of this ion impact-melting-induced, self-organized pattern formation mechanism probing the compound semiconductor GaSb under polyatomic Au ion irradiation with various irradiation conditions. Surprisingly, GaSb irradiated with 30 keV dimer gold ions at 200°C and normal incidence shows faceted crystalline nanostructures, see Fig. 1 [6].
Calculations of the needed melting energies per atom (Emelt) for different materials show, that among others GaSb is a preferring candidate for a successful surface patterning by mon- and polyatomic heavy ions whereas for instance the surface of SiC remains stable under the comparable conditions. Furthermore the surface modification behavior under polyatomic Gold and Bismuth heavy ion impact should be compared.
HR-SEM, AFM and EDX analysis of irradiated surfaces reveal that for compound semiconductors, additional superstructures are evolving on top of the regular semiconductor dot patterns, indicating superposition of a second dominant driving force for pattern self-organization.

References:

[1] C. Anders, K.-H. Heinig and H. M. Urbassek, Polyatomic bismuth impacts into germanium: Molecular dynamics study, Phys. Rev. B 87 (2013) 245434.
[2] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, and W. Pilz, Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions, Nucl. Instr. and Meth. B 272 (2012) 198.
[3] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, From sponge to dot arrays on (100)Ge by increasing the energy of ion impacts, Journal of Vacuum Science and Technology B 30 (2012) 06FF12.
[4] R. Böttger, K-.H Heinig, L. Bischoff, B. Liedke, R. Hübner, and W. Pilz, Silicon nanodot formation and self-ordering under bombardment with heavy Bi3 ions, physica status solidi – Rapid Research Letters 7 (2013) 501.
[5] L. Bischoff, R. Böttger, K.-H. Heinig, S. Facsko, and W. Pilz, Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions, Applied Surface Science 310 (2014) 154.
[6] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender and S. Facsko, Faceted nanostructure arrays with extreme regularity by self-assembly of vacancies, Nanoscale 7 (2015) 18928.