Single GaAs/AlAs nanowire in magnetic field
It is now possible to grow using molecular beam epitaxy (MBE) defect free GaAs/AlAs core/shell nanowires (NWs) with optical properties approaching those of the best optical quality MBE grown GaAs. In contrast to 3D GaAs, core/shell NWs give bright emission at room temperature opening the way for numerous optoelectronic applications. Furthermore, the NWs can be grown with GaAs in the zinc-blende or wurzite phase, the latter phase being unique to NWs.
Magnetic field, which couples to both the orbital and the spin degree of freedom, can be used to investigate the fascinating physics of confined one dimensional excitons. The diamagnetic shift gives information on the extent of the exciton wave function and the associated orbital quantum number. Alternatively, the coupling to the spin degree of freedom leads to a Zeeman splitting of the exciton lines at high field giving information concerning the electron and hole g-factors and many body interactions.
Fig.1 Typical emission spectra from single GaAs/AlAs nanowire together with the magnetic field evolution of the emission. The colour plot shows differential μPL spectra to highlight the evolution of the emission as a function of magnetic field at T = 1.7 K. Several sharp emission lines are resolved which exhibit a large diamagnetic shift and Zeeman splitting at high magnetic fields.
Measurements performed in high magnetic field allowed us to detect in the emission several lines associated with excitons bound to defect pairs. Such lines were previously observed in epitaxial GaAs of very high optical quality, as reported by Kunzel and Ploog. This demonstrates that the optical quality of our GaAs/AlAs core/shell nanowires is comparable to the best GaAs layers grown by molecular beam epitaxy. Moreover, strong free exciton emission is observed even at room temperature.