On the Luminescence of VLS-grown GaAs-AlGaAs Core-Shell Nanowires and its Dependence on MOVPE Growth Conditions
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1206-M11-36
On the luminescence of VLS-grown GaAs-AlGaAs core-shell nanowires and its dependence on MOVPE conditions P. Prete,1 N. Lovergine,2 I. Miccoli,2 F. Marzo,2 J.S. Burger,2,# G. Salviati,3 and L. Lazzarini 3 1 IMM-CNR, Lecce Research Unit, Lecce, Italy 2 Dept. of Innovation Engineering, University of Salento, Lecce, Italy 3 IMEM-CNR, Parma, Italy ABSTRACT We report on the photoluminescence (PL) of GaAs-Al0.32Ga0.68As core-shell nanowires grown by MOVPE, and their dependence on the precursors V:III molar ratio utilized in the vapor during growth. It is shown that the PL emission of the GaAs nanowire core red-shifts with decreasing the V:III ratio from 30:1 to 4:1, an effect tentatively ascribed to the build-up of a space-charge region at the core-shell hetero-interface, the latter associated to the unintentional incorporation of impurities, namely C in GaAs and Si in AlGaAs. INTRODUCTION The growth of III-V nanowires and related 1-dimensional (1d) nanostructures through the socalled Vapor-Liquid-Solid (VLS) growth mechanism [1], is a most promising bottom-up technology for the synthesis of novel nanowire-based devices. MOVPE growth of 1d heterostructures with compositional modulation along the nanowire radial direction (core-shell nanowires) has been demonstrated for both GaAs-GaInP [2] and GaAs-AlGaAs [3,4,5]. Indeed, growth of a larger band-gap material shell around a GaAs nanowire enhances the nanowire radiative efficiency [2]; besides, changing the shell band-gap allows to control the carrier confinement within the GaAs core and may also improve the optical confinement of the photons by acting as an optical cavity. The use of AlGaAs as shell material ensures an almost strain-free core-shell structure, simplifying the analysis of the nanowire electronic and optical properties. We have previously reported on the luminescence of GaAs-AlGaAs core-shell nanowires grown by MOVPE using tertiarybutylarsine (tBuAsH2) and demonstrated that nanostructures with good radiative properties can be grown under relatively low precursors V:III ratios in the vapor [5]. In this paper, we further study the effect of changing the precursors V:III ratio during the growth of the GaAs core and/or the AlGaAs shell on the nanowire photoluminescence (PL) properties. EXPERIMENT GaAs/AlGaAs core-shell nanowires were grown on (111)B-GaAs substrates using trimethylgallium (Me3Ga), trimethylaluminium (Me3Al), and tBuAsH2. GaAs substrates were first degreased in iso-propanol vapors for 1 h, etched in a H2SO4:H2O2:H2O (4:1:2) solution for 8 min at 40°C, rinsed in deionized water and finally dried under pure N2. Au nanoparticles (NPs) prepared in colloidal solution and deposited on the freshly etched substrates, as reported in ref. [6], were used as catalysts for the VLS growth of GaAs nanowire cores; the sample average NP surface densities were in the 108−109 cm-2 range. Cylindrically-shaped (untapered) and kink-free GaAs nanowires well-aligned in the [111]B substrate direction were grown at 400°C [6], with #
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