Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene

Graphene offers new opportunities to improve the performance and functionalities of optoelectronic devices based on III−V compound semiconductors. The transparency and high in-plane electrical conductivity of graphene and few-layer graphene films is of interest for the fabrication of contact layers in light-emitting diodes (LEDs), solar cells, and photodetectors, especially in the deep-UV spectral region where standard indium tin oxide contacts are not transparent. At the same time, its high thermal conductivity is potentially helpful to dissipate heat, a major issue when light emitters are operated at high currents. Furthermore, provided that III−V compounds could be synthesized with high structural perfection on graphene, the flexibility of this material as well as the possibility to be grown or transferred onto different substrates may enable the integration of III−V based devices with otherwise incompatible material systems such as the complementary metal-oxide-semiconductor (CMOS) platform.

Figure 1. (a) Bird's eye view scanning electron micrograph of a GaN nanowire ensemble prepared on an epitaxial multilayer graphene (MLG) film synthesized on SiC. (b) High-resolution cross-sectional transmission electron micrograph revealing the presence of a continuous multilayer graphene film between the GaN nanowires and the SiC substrate.

In this work, we demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene films. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates.

1 Author S. Fernández-Garrido , M. Ramsteiner , G. Gao , L. A. Galves , Bharat Sharma , P. Corfdir , G. Calabrese , Z. de Souza Schiaber , C. Pfüller , A. Trampert , J. M. J. Lopes , O. Brandt , L. Geelhaar

Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene

Source Nano Lett. , 17 , 5213 ( 2017 )
DOI : 10.1021/acs.nanolett.7b01196 | 2906 Cite : Bibtex RIS
S. Fernández-Garrido, M. Ramsteiner, G. Gao, L. A. Galves, Bharat Sharma, P. Corfdir, G. Calabrese, Z. de Souza Schiaber, C. Pfüller, A. Trampert, J. M. J. Lopes, O. Brandt, and L. Geelhaar