Ultrafast laser deposition of semiconductor nanowires

Pulsed laser deposition (PLD) has been applied to fabricate thin films of a variety of materials. However, formation of micron-sized particulates during conventional nanosecond laser-based deposition process makes it unsuitable for growing high quality nanoscale materials. Owing to a nonequilibrium non-thermal ablation mechanism and characterized by their short pulse duration compared to thermal diffusion time (tens of picoseconds), ultrafast laser pulses are able to produce particulate-free precursor vapor for nanoscale material deposition. In this article, the foundation of non-thermal ultrafast laser ablation will be examined by both experimental and theoretical investigation:;. Ultrafast laser-induced high-density electron ejection and subsequent build-up of a strong electric field above the target material were observed. Mass spectrometry and electron microscopy measurements confirmed the particulate-free nature of ultrafast laser ablation. Using ultrafast laser-based particulate-free PLD approach, high quality ZnO nanowires were grown on sapphire and silicon substrates. The optical properties of ZnO nanowires, including the external and internal quantum efficiency of nanowire nanolasers, were experimentally determined. In addition, a nanowire UV photodiode based on p-Si/n-ZnO nanowires was successfully fabricated. This first nanowire photodiode device shows good photocurrent characteristics when operated under reverse bias.