Aluminum catalyzed growth of silicon nanowires: Al atom location and the influence of silicon precursor pressure on the morphology

Abstract

We study the growth of silicon nanowires (SiNWs) by chemical vapor deposition (CVD) with aluminum as catalyst. We show that for a growth temperature of 600°C, the silicon precursor partial pressure (SiH4 in this study) is a key parameter for controlling the structural quality of the resulting SiNWs. We find by transmission electron microscopy that at high SiH4 partial pressure, the SiNWs are composed of a monocrystalline core with a high density of surface defects, mainly twins, sheathed by a rough amorphous silicon layer. By contrast, at low SiH4 partial pressure, the SiNWs are monocrystalline with a lower density of surface crystalline defects and a smooth surface. For the low SiH4 partial pressure SiNWs, Al atoms have been detected at the SiNW surface by Auger spectroscopy at level around 3at% and in the SiNW core by energy dispersive X-ray spectroscopy (EDS) at levels around 1at%. Interestingly, higher Al concentrations are measured inside the nano-twin domains by EDS (around ten times increase). Two possible explanations are proposed; stacking faults are induced by Al atoms that lower their energy formation, or Al atoms can be trapped inside these stacking faults due to segregation effect during growth. These findings will be important for growing high quality SiNWs using Al as metal catalyst in reduced-pressure CVD tool.