Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 13: Focus Session: Functional Semiconductor Nanowires I (organized by HL)
TT 13.3: Vortrag
Montag, 16. März 2015, 10:15–10:30, EW 201
Stability of heteroepitaxial coherent growth modes on nanowire radial surfaces — •Thomas Riedl1,2 and Jörg Lindner1,2 — 1University of Paderborn, Department of Physics, Warburger Straße 100, 33098 Paderborn, Germany — 2Center for Optoelectronics and Photonics Paderborn (CeOPP), Warburger Straße 100, 33098 Paderborn, Germany
Semiconductor nanowires (NWs) exhibit a large surface-to-volume ratio and are therefore interesting as a substrate for the growth of nanoscale heteroepitaxial islands as well as core-shell structures for use in optoelectronic applications. Compared to planar substrates the NW curvature leads to a modified thermodynamic stability of the coherent Frank-van-der-Merwe and Stranski-Krastanov (SK) heteroepitaxial growth modes. In the present contribution we investigate the stability of these growth modes on cylindrical NWs by means of continuum theory. In contrast to previous studies (i) the exact geometrical shape of pyramidal islands and (ii) the impact of the island contact angle on the elastic relaxation energy are considered. Maps of the growth mode stability are derived for the Si core / Ge shell structure, which display the favoured mode as a function of deposited volume, wetting layer thickness and NW radius. When using a Ge surface energy of 1.3 J/m2 for both the shell and the pyramid surfaces the SK mode becomes stable only for large contact angles and NW radii larger than 40 nm. However, if the reduced surface energy of low-index Ge facets is taken into account, the transition between the two growth modes is shifted to smaller NW radii, as observed in experiments.