III-V Nanowires on Si for optoelectronics and Solar applications

Anna Fontcuberta i Morral, Eleonora Russo-Averchi, Yannik Fontana, Anna Dalmau-Mallorqui, Martin Heiss, Sonia Conesa-Boj, Daniel Rüffer, Emanuele Uccelli

Laboratory of Semiconductor Materials, Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland

Nanowires are filamentary crystals with a diameter in the order of few to hundred nanometers. In the last few years it has been shown that their particular morphology leads to novel properties and opens new avenues for applications in the area of optoelectronics and energy harvesting. To industry, it is particularly appealing the possibility of integrating defect-free III-V materials on silicon, which his possible in the form of nanowire.
For nanowires to become a reality in device applications, the synthesis of nanowires, complex heterostructures and doping should be mastered. Moroever, for a realistic integration in the silicon industry, the use of gold as nucleation seed should be avoided. It has been shown that Molecular Beam Epitaxy (MBE) is able to produce gold-free III-V nanowires with excellent optoelectronic properties [1,2]. We believe this technique offers a model system to understand growth phenomena and to provide materials with high purity and atomically sharp heterostructures.
We will present our results in the growth of GaAs nanowires by the gallium-assisted method [3]. We will explain the growth mechanisms and how they can be adapted to mismatched substrates such as silicon [4]. Other semiconductors such as InAs will be presented. Then we will proceed on how the optical properties of GaAs nanowires can be modified by adding heterostructures, such as quantum wells and quantum dots [5]. The optical properties will be elucidated by confocal photoluminescence spectroscopy.
Finally, we will show how these nanowires can be obtained in ordered arrays, opening new perspectives of III-V nanowires in photovoltaics [6,7]. We will present our recent results in this area.

[1] A. Fontcuberta i Morral et al. Small 4, 899 (2008)
[2] D. Spirkoska et al., Phys. Rev. B 80, 245325 (2009);
[3] C. Colombo et al, Phys. Rev. B, 77, 155326 (2008);
[4] E. Uccelli et al, Nano Lett. 11, 3827 (2011), E. Russo-Averchi et al, Nanoscale 4, 1486 (2012)
[5] E. Uccelli et al, ACS Nano 4, 5985 (2010).
[6] C. Colombo et al.,  Appl. Phys. Lett. 94, 173108 (2009)
[7] A. Dalmau-Mallorqui et al, submitted (2012)