Low temperature photoluminescence and Raman phonon modes of Au-catalyzed MBE-grown GaAs–AlGaAs core–shell nanowires grown on a pre-patterned Si (1 1 1) substrate

Abstract

We present the optical properties of MBE-grown GaAs–AlGaAs core–shell nanowires (NWs) grown on anodized-aluminum-oxide (AAO) patterned-Si (1 1 1) substrate using photoluminescence and Raman scattering spectroscopy. The GaAs NWs were grown via the vapor–liquid–solid method with Au-nanoparticles as catalysts. Enhancement in emission of at least an order of magnitude was observed from the GaAs–AlGaAs core–shell NWs as compared to the bare GaAs NWs grown under similar conditions, which is an indication of improved radiative efficiency. The improvement in radiative efficiency is due to the passivating effect of the AlGaAs shell. Variation in bandgap emission energy as a function of temperature was analyzed using the semi-empirical Bose–Einstein model. Results show that the free exciton energy of the GaAs core–shell agrees well with the known emission energy of zinc blende (ZB) bulk GaAs. Further analysis on the linear slope of the temperature dependence curve of photoluminescence emission energy at low temperatures shows that there is no difference between core–shell nanowires and bulk GaAs, strongly indicating that the grown NWs are indeed predominantly ZB in structure. The Raman modes show downshift and asymmetrical broadening, which are characteristic features of NWs. The downshift is attributed to lattice defects rather than the confinement or shape effect.