Surface smoothing and native oxide suppression on Zn doped aerotaxy GaAs nanowires

Abstract

Aerotaxy, a recently invented aerosol-based growth method for nanostructures, has been shown to hold great promise in making III-V nanowires more accessible for cheap mass-production. Aerotaxy nanowire surface structure and chemistry, however, remains unexplored, which is unfortunate since this can influence (opto)electronic properties. We investigate the surfaces of aerotaxy grown GaAs nanowires using synchrotron based high resolution X-ray photoelectron spectroscopy and high resolution atomic force microscopy. We observe that increasing the concentration of the p-type dopant diethylzinc to very high levels during nanowire growth significantly changes the surface morphology and leads to a strong suppression of native surface oxide formation. Our findings indicate that up to 1.8 monolayers of Zn are present on the nanowire surface after growth. Finally, we find that this also influences the Fermi level pinning of the surface. We suggest that Zn present on the surface after growth could play a role in the strongly hindered oxidation of the III-V compound when exposed to air. The aerotaxy nanowires generally exhibit a round cross section, while a significant smoothening of the surface morphology along the nanowire appears for very high nominal doping levels likely as a result of slight reshaping during growth in the presence of Zn. Given that surface oxide and a rough morphology can be detrimental to nanowire electrical and optical performance, the ability to reduce them as a side effect of dopant introduction will benefit future applications. Finally, the observed hindering of oxidation during air transport can allow for reliable post-growth processing in separate systems.