Epitaxial growth of GaN nanowires with high structural perfection on a metallic TiN film

The bottom-up growth of free-standing nanowires has opened up new opportunities for the epitaxial combination of dissimilar materials, because strain induced by mismatch in lattice constants can elastically relax at the free nanowire sidewalls. Here, we take the level of dissimilarity between nanowire and substrate material to a new level and demonstrate the growth of semiconductor nanowires with high structural perfection on a metallic substrate. In this case, the two materials differ not only in lattice constant, but also in crystal structure and type of chemical bonding.

Scanning electron micrograph of the GaN nanowires grown on TiN in bird's eye view. The length of well-developed nanowires is 300 nm, and they are typically 20 to 40 nm thick.

Our strategy has been to employ the strong tendency of GaN to spontaneously form single-crystalline nanowires under suitable growth conditions. As a substrate, we have chosen TiN because this material is chemically as well as thermally very stable and exhibits metallic conductivity. Our experiments have demonstrated that the growth of GaN by molecular beam epitaxy indeed results also on a TiN film in vertical nanowires. In-situ electron diffraction has evidenced that these nanowires have a strict epitaxial relationship to the TiN film. Photoluminescence spectroscopy has shown excitonic GaN transitions virtually identical in spectral position, linewidth and decay time to those of state-of-the-art GaN nanowires grown on Si. Therefore, the crystalline quality of the GaN nanowires grown on metallic TiN and on Si is equivalent. The freedom to employ metallic substrates for the epitaxial growth of semiconductor nanowires in high structural quality may enable novel applications that benefit from the associated high thermal and electrical conductivity as well as optical reflectivity.

1 Author M. Wölz , C. Hauswald , T. Flissikowski , T. Gotschke , S. Fernández-Garrido , O. Brandt , H. T. Grahn , L. Geelhaar , H. Riechert

Epitaxial growth of GaN nanowires with high structural perfection on a metallic TiN film

Source Nano Lett. , 15 , 3743 ( 2015 )
DOI : 10.1021/acs.nanolett.5b00251 | 2698 Cite : Bibtex RIS
M. Wölz, C. Hauswald, T. Flissikowski, T. Gotschke, S. Fernández-Garrido, O. Brandt, H. T. Grahn, L. Geelhaar, and H. Riechert