Germanium nanowires with 3-nm-diameter prepared by low temperature vapour-liquid-solid chemical vapour deposition

We report the growth of germanium nanowires (Ge NWs) with single-step temperature method via vapour-liquid-solid (VLS) mechanism in the low pressure chemical vapour deposition (CVD) reactor at 300 °C, 280 °C, and 260 °C. The catalyst used in our experiment was Au nanoparticles with equivalent thicknesses of 0.1 nm (average diameter ∼3 nm), 0.3 nm (average diameter ∼4 nm), 1 nm (average diameter ∼6 nm), and 3 nm (average diameter ∼14 nm). The Gibbs-Thomson effect was used to explain our experimental results. The Ge NWs grown at 300 °C tend to have tapered structure while the Ge NWs grown at 280 °C and 260 °C tend to have straight structure. Tapering was caused by the uncatalysed deposition of Ge atoms via CVD mechanism on the sidewalls of nanowire and significantly minimised at lower temperature. We observed that the growth at lower temperature yielded Ge NWs with smaller diameter and also observed that the diameter and length of Ge NWs increases with the size of Au nanoparticles for all growth temperatures. For the same size of Au nanoparticles, Ge NWs tend to be longer with a decrease in temperature. The Ge NWs grown at 260 °C from 0.1-nm-thick Au had diameter as small as ∼3 nm, offering an opportunity to fabricate high-performance p-type ballistic Ge NW transistor, to realise nanowire solar cell with higher efficiency, and also to observe the quantum confinement effect.