Ion-induced nanopatterning of GaAs and InAs (001) surfaces and possible applications in bottom-up nanostructure fabrication

Periodic nanostructure arrays are sought-after for advanced photovoltaics, high-sensitivity biomolecule detection, and future information technology. One cost-effective bottom-up approach to fabricate such nanostructure arrays is templated growth on spontaneously nanopatterned surfaces, which can be achieved on semiconductors by low energy ion irradiation [1]. We studied the influence of process parameters such as ion energy and fluence, substrate temperature, and ion incidence angles on the resulting nanoscale morphologies of GaAs and InAs surfaces.

If the semiconductor surface is irradiated with low-energy ions above the recrystallization temperature of the material, the surface remains crystalline. In the so-called reverse epitaxy regime, the diffusion of the ion-induced vacancies and ad-atoms on the crystalline surface is subject to the Ehrlich-Schwoebel barrier, an energy barrier for crossing terrace steps. In analogy to epitaxial growth, for ion irradiations performed in a specific energy and temperature range this can lead to the formation of well-defined faceted surface structures [2]. The resulting surface morphology is strongly dependent on the crystalline structure of the semiconductor substrate. For instance, GaAs(001) and InAs(001) surfaces exhibit regular ripple structures with a saw tooth profile oriented along the [1-10] direction. For this pattern formation to take place, InAs must be kept in a temperature range between 160°C and 430 °C, while GaAs requires sample temperatures of at least 430 °C. Increasing the ion energy increases the ripple periodicity, and so does increasing the sample temperature at lower ion energies. The order of the pattern increases with increasing ion fluence and, for InAs, with increasing ion energy.

Such nanorippled surfaces can for example be employed as substrates for physical vapor deposition under various incidence angles, producing periodic arrays of nanowires, periodically corrugated thin films, or combinations thereof. Furthermore, epitaxial growth is expected on these crystalline surfaces for materials with low lattice mismatch.

[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou et al., Nanoscale 7 (2015).