Atomically sharp catalyst-free wurtzite $GaAs∕AlGaAs$ nanoneedles grown on silicon

We report a catalyst-free, self-assembled growth mode generating single-crystal wurtzite phase ultrasharp $GaAs∕AlGaAs$ nanoneedles on both GaAs and Si substrates via low-temperature metal-organic chemical vapor deposition. The needles exhibit record-narrow tip diameters of $2–4nm$ wide and sharp 6°–9° taper angles. The length is dependent on growth time and up to $3–4μm$ nanoneedles are attained. The structures do not exhibit twinning defects, contrary to typical GaAs nanowires grown by vapor-liquid-solid catalyzed growth. AlGaAs layered nanoneedle structures are also demonstrated.