Luminescence Of Gaas/algaas Core-shell Nanowires Grown By Movpe Using Tertiarybutylarsine

摘要

The luminescence properties of GaAs/AlGaAs core-shell nanowires grown by metalorganic vapor phase epitaxy (MOVPE) on (111)B GaAs using tertiarybutylarsine, trimethylgallium and trimethylaluminium are reported. Untapered kink-free GaAs nanowires with average diameters around 50-70 nm were grown at 400℃ by the vapour-liquid-solid method; to this purpose, colloidal Au nanoparticles were used as metal catalyst. Al_(0.33)Ga_(0.67)As shells were grown at 650℃ around GaAs nanowires by conventional MOVPE, with thickness ranging in the 70-160 nm interval. Low-temperature photo-luminescence (PL) and high spatial resolution cathodoluminescence (CL) measurements were performed, respectively, on dense ensembles of core-shell nanowires (still on their original substrates) and single nanowires; comparison between secondary electron and monochromatic CL images of single nanowires led to spatially resolve the major CL emissions. The low-temperature luminescence of nanowires above the GaAs band-gap energy consists of three contributions: (ⅰ) the 1.997 eV band-edge (excitonic) emission of the Al_(0.33)Ga_(0.67)As shell, followed (in CL spectra) by a more intense GaAs-like LO-phonon replica; (ⅱ) a broad weaker band at ～1.90 eV, ascribed to a donor-acceptor pair recombination associated to residual Si donors in the AlGaAs; and (iii) a dominant and very broad band at ～1.67 eV, due to the spatially indirect recombination between electrons in the core and holes in the shell. Comparison between CL and PL spectra suggests that each nanowire has a slightly different GaAs core emission, its peak energy varying in the 1.46-1.49 eV interval.