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.
Highlights
III-V semiconductor nanowires (NWs) are considered to play an important part in the generation of high-speed electronics,[1,2] light emitting diodes (LEDs),[3,4] and energy harvesting devices such as solar cells.[5,6] GaAs, in particular, is the most studied and used III-V bulk material, and GaAs NWs are relevant for solar cell[7] and laser applications.[8]
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
From synchrotron radiation X-ray photoelectron spectroscopy (XPS) studies, we conclude that NWs with different doping have different amounts of oxides on the surface, and we propose that excess Zn adsorption on the surface reduces the amount of native oxides of the NWs
Summary
III-V semiconductor nanowires (NWs) are considered to play an important part in the generation of high-speed electronics,[1,2] light emitting diodes (LEDs),[3,4] and energy harvesting devices such as solar cells.[5,6] GaAs, in particular, is the most studied and used III-V bulk material, and GaAs NWs are relevant for solar cell[7] and laser applications.[8]. Synchrotron based X-ray photoelectron spectroscopy (XPS) is a powerful tool for obtaining quantitative information about the exact surface chemistry It allows the choosing of suitable energies, making the technique surface sensitive and providing information about native oxides residing on the topmost few atomic layers of the surface of the NWs. There are several reports on oxides on epitaxially grown III-V NWs,[16,20] and the interaction between various III-V NWs and oxide films has been characterized in detail.[21]. We report on the surface oxide chemistry and morphology of aerotaxy grown NWs. We show synchrotron based XPS results of three differently p-doped growth batches of aerotaxy GaAs NWs. We analyze the native oxides on the NW surface, and we correlate a decrease in NW oxide formation to the presence of Zn during growth. While the round cross section was similar for all samples, it was found that the samples with Zn present during growth show a smoother surface axially along the NW growth direction
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