Synthesis and optical properties of high-quality ultrathin homogeneous GaAs1−xSbx nanowires

Ternary GaAs_1−xSb_x nanowires with designable bandgaps and lattice constants show important potential applications in band structure engineering as well as optical and optoelectronic devices. However, large diameters, low aspect ratios and even spontaneous core-shell structures are always found in GaAs_1−xSb_x nanowires, which are hindering their optical and optoelectronic applications. Here, we report the controlled synthesis of ultrathin GaAs_1−xSb_x nanowires on Si (111) substrates by molecular-beam epitaxy. It is found that ultrathin GaAs_1−xSb_x nanowires with a diameter less than 40 nm and an aspect ratio exceeding 35 can be obtained by precisely tuning the Ga flux and the growth temperature. The growth of the ultrathin GaAs_1−xSb_x nanowires with a large-composition-range (0 ⩽ x ⩽ 0.4) are also achieved by directly tuning the antimony flux. Detailed structural studies confirm that these ultrathin nanowires exhibit high crystal-quality, and no spontaneous core-shell nanostructures are observed along the axial and radial directions of the nanowires. As far as we known, it is the first time that homogeneous GaAs_1−xSb_x nanowires are grown by molecular-beam epitaxy. Photoluminescence measurements prove that the ultrathin GaAs_1−xSb_x nanowires have a narrower full width at half maximum of the photoluminescence peak compared with those results reported in the literatures, and their emission wavelengths can be tuned from 850 nm (GaAs) to 1271 nm (GaAs_0.6Sb_0.4). In addition, the optical properties of the ultrathin GaAs_1−xSb_x nanowires can be further improved by using the Al_0.5Ga_0.5As shell as a passivation layer. Our work lays a foundation for the development of high-performance GaAs_1−xSb_x nanowire-based optical and optoelectronic devices.