Magneto-Optical Properties of Wurtzite-Phase indium phosphide Nanowires

Researchers from the HFML Nijmegen, in collaboration with scientists of Sapienza Università di Roma (Italy) and the Australian National University (Canberra, Australia), have characterized the properties of wurtzite-phase indium phosphide nanowires. They have found that the reduced effective mass and gyromagnetic factor of the band edge exciton in the wurtzite crystal-phase are significantly different from those of the usual zincblende phase. These findings enrich the understanding of the electronic properties of nanowires, which have great potential in many nanoelectronic applications. The results are published in Nano Letters on 27 June 2014.

The possibility to grow semiconductor nanowires in different crystal structures widens their potential in realizing novel nano-electronic and –optical applications. This is particularly true in technologically relevant III–V compounds, such as gallium arsenide, indium arsenide and indium phosphide, which adopt exclusively the zincblende crystal phase in bulk, but which can be grown in the wurtzite phase in a nanowire. Yet, the physical properties of the wurtzite phase are almost experimentally unknown.

By measuring the optical emission of high quality wurtzite indium phosphidena nowires (Figure left panel) in intense magnetic fields (B) up to 28 T, the transport and spin properties of the wurtzite crystal-phase have been determined. Through application of the magnetic field along different crystallographic directions the value and the anisotropy of the reduced effective mass and the gyromagnetic (g-factor)of the band edge exciton have been quantified (Figure right panel). A sizable increase (14%) in the exciton reduced mass with respect to that measured in zincblende bulk has been found. A small degree (6%) of anisotropy of the reduced mass with respect to the crystallographic ĉ axis has been derived. A stronger anisotropy has been found in the Zeeman splitting, which for B^ĉ is nearly half of that found for B//ĉ. The electron g-factor (|1.4|) is slightly greater than its counterpart in zincblende and the g-factor for holes appears to depend on magnetic field for |B|> 17 T. Finally, under the effect of magnetic field a 20% circular polarization dichroism of the emitted photons is observed for the Faraday configuration only, in agreement with the wurtzite phase of the nanowires. These results enrich the understanding of the electronic properties of nanowires and prompt further investigations of this material system that has great potential in many nanoelectronic applications.

Left: High-resolution transmission electron microscopy characterization of the InP nanowires, evidencing the high quality of the wurtzite material. Right: Magnetic-field dependence of the shift in exciton energy, with respect to zero field, for Voigt (B^ĉ) and Faraday (B//ĉ) configurations. Both shift (reduced mass) and splitting (g-factor) depend on the relative directions of the magnetic field B and the crystallographic ĉ axis, permitting a full characterization of the physical properties of wurtzite phase InP nanowires.

Reference

Magneto-Optical Properties of Wurtzite-Phase InP Nanowires, M. De Luca, A. Polimeni, H. A. Fonseka, A. J. Meaney, P. C. M. Christianen, J. C. Maan, S. Paiman, H. H. Tan, F. Mura, C. Jagadish, and M. Capizzi, Nano Letters 14, 4250–4256 (2014).