Semiconductor nanowires are routinely grown on high-priced crystalline substrates as it is extremely challenging to grow directly on plastics and flexible substrates due to high temperature requirements and substrate preparation. At the same time plastic substrates can offer many advantages such as extremely low price, light weight, mechanical flexibility, shock and thermal resistance and biocompatibility. We explore the direct growth of high quality III-V nanowires on flexible plastic substrates by metalorganic vapor phase epitaxy. We synthesize InAs and InP nanowires on polyimide and show that the fabricated NWs are optically active with strong light emission in the mid-infrared range. We create a monolithic flexible nanowire-based p-n junction device on plastic in just two fabrication steps. Overall, we demonstrate that III-V nanowires can be synthesized directly on flexible plastic substrates inside a MOVPE reactor, and we believe that our results will further advance the development of the nanowire-based flexible electronic devices.

Fermi level pinning at the oxidized (110) surfaces of III-As nanowires (GaAs, InAs, InGaAs, AlGaAs) is studied. Using scanning gradient Kelvin probe microscopy, we show that the Fermi level at oxidized cleavage surfaces of ternary Al _x Ga _{1− x} As (0 ≤ x ≤ 0.45) and Ga _x In _{1− x} As (0 ≤ x ≤ 1) alloys is pinned at the same position of 4.8 ± 0.1 eV with regard to the vacuum level. The finding implies a unified mechanism of the Fermi level pinning for such surfaces. Further investigation, performed by Raman scattering and photoluminescence spectroscopy, shows that photooxidation of the Al _x Ga _{1− x} As and Ga _x In _{1− x} As nanowires leads to the accumulation of an excess of arsenic on their crystal surfaces which is accompanied by a strong decrease of the band-edge photoluminescence intensity. We conclude that the surface excess arsenic in crystalline or amorphous forms is responsible for the Fermi level pinning at oxidized (110) surfaces of III-As nanowires.