Fine structure of excitons in InAs quantum dots on GaAs(110) planar layers and nanowire facets

We investigate the optical properties of InAs quantum dots grown by molecular beam epitaxy on GaAs(110) using Bi as a surfactant. The quantum dots are synthesized on planar GaAs(110) substrates as well as on the {110} sidewall facets of GaAs nanowires. At 10 K, neutral excitons confined in these quantum dots give rise to photoluminescence lines between 1.1 and 1.4 eV. Magneto-photoluminescence spectroscopy reveals that, for small quantum dots emitting between 1.3 and 1.4 eV, the spatial extent of the exciton wave function in and perpendicular to the (110) plane is about 5 and 2 nm, respectively. The quantum dot photoluminescence is linearly polarized, and biexcitons with positive as well as negative binding energies are observed, two findings that we associate with the strain in the (110) plane. This strain leads to piezoelectric fields and to a strong mixing between heavy- and light-hole states, and offers the possibility to tune the degree of linear polarization of the exciton photoluminescence as well as the sign of the binding energy of biexcitons.