The morphology of silicon nanowires grown in the presence of trimethylaluminium.

The effects of trimethylaluminium (TMA) on silicon nanowires grown by chemical vapour deposition (CVD) were investigated in the 650-850 degrees C growth temperature range. Gold was used as the growth catalyst and SiH4 in H2 carrier gas as the Si precursor. Depending on substrate temperature and TMA partial pressure, the structure's morphology evolves from wires to tapered needles, pyramids or nanotrees. The TMA presence was linked to two specific growth modes: an enhanced surface growth which forms Si needles and a branched growth leading to Si nanotrees. We suggest that competition between these two specific growth modes and the usual Au-catalyzed VLS growth is responsible for the observed morphology changes.