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High Magnetic Field Reveals the Nature of Excitons in a Single GaAs/AlAs Core/Shell Nanowire

Single NWs have been proposed for several applications in electronics, opto electronics or photo voltaics. In contrast to bulk material, III-V nanowires can crystallize in wurzite, zinc blende or mixed crystal structures. The different crystal structures have different electronic band structures, giving us a tool to manipulate the optical and electronic properties of the NWs. Therefore studying the excitonic behavior in GaAs NWs is an important part of the description and understanding of their electronic properties.

High magnetic fields are a unique and powerful tool to reveal the nature of excitons in single high aspect ratio GaAs/AlAs core/shell nanowires (NWs). We show for the first time that emission from a single NW exhibits very strong and narrow excitonic lines. This demonstrates the extremely high quality of our nanowires and proves that their quality approaches that of the best bulk material. The application of a magnetic field probes both the orbital and spin degrees of freedom. The magnetic field dependence of the emission allows us to identify unambiguously the emission with the recombination of excitons bound to defect pairs with different separations, previously observed only in very high quality MBE grown GaAs.

Our NWs, easily dispersed onto a Si substrate, should open the way for numerous optoelectronic applications based on well-established Si device technology. Additionally, our NWs have a pure zinc blende structure, which is the well-pursued structure for GaAs devices. Our results should increase the understanding of the band structure of single GaAs NWs, which is crucial for the many possible applications.

Differential PL spectra showing the evolution of the emission as a function of magnetic field applied perpendicular to the NW at T = 1.7K. Several sharp emission lines are resolved, which show a large diamagnetic shift and Zeeman splitting at high magnetic fields. The white symbols show for comparison the shift of the strong line (14) of the bound exciton-defect pair recombination in epitaxial GaAs of Skolnick et al. [Skolnick et al., Phys. Rev. B 38, 4165 (1998)]

Ref.: Plochocka et al., NanoLetters 2013