In this work we present methods for overcoming these lattice-mismatched epitaxial limitations. Au-catalyzed vapor-liquid-solid nanowire growth is conducted via metal-organic chemical vapor deposition, and material-dependent critical diameters are discussed. Experimental results are presented which support theoretical predictions of a critical nanowire maximum diameter for epitaxial growth. A model is developed which predicts the nanowire growth rate, and dependence of the crystal phase on the nanowire diameter observed in experiments.
We also present a new growth mode which produces III-V nanoneedles via metal-organic chemical vapor deposition. The nanoneedles are catalyst-free, ultra-sharp GaAs-based structures, with record narrow tip diameters of less than 1 nm, sharp 6-9 degree taper angles, and lengths up to 10 um. The crystals are pure wurtzite phase crystal, free of zincblende phases, which is uncommon for GaAs. The nanoneedles grow on GaAs, silicon and sapphire substrates and exhibit bright room-temperature photoluminescence. The growths are conducted at 380 to 420 degrees C, making the process ideal for silicon-CMOS integration. The nanoneedles can also be large enough for device fabrication using top-down, standard processing techniques.
Growth of ternary nanoneedles is also demonstrated, specifically, pure InGaAs nanoneedles. The InGaAs nanoneedles exhibit similar structural properties as the GaAs nanoneedles, being single-crystal, with bright photoluminescence and ultra-sharp tips. Core-shell heterostructure nanoneedles of InGaAs and AlGaAs are also demonstrated. InGaAs quantum well nanoneedles having near-band-edge emission tunable by 380 meV are also shown, with photoluminescence emission below the silicon absorption edge, facilitating use of integrated passive silicon devices.
Transmission electron microscopy analysis of the nanoneedles is also presented. The results elucidate the uniform crystal phase and lattice constants, and show the ultra-sharp tips of the nanoneedles of the different III-V nanoneedle compositions grown on the various substrates.