Photodegradation of Si-doped GaAs nanowire

Researching optical effects in nanowires may require a high pump intensity which under ambient conditions can degrade nanowires due to thermal oxidation. In this work we investigated the photodegradation of a single Si-doped GaAs nanowire by laser heating in air. To understand the changes that occurred on the nanowire we carried out Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy in laser damaged regions as well as in non-affected ones. From Raman Stokes and anti-Stokes measurements we estimated the local temperature that the oxidation process of the nanowire (NW) surface starts at as 661 K, resulting in two new Raman modes at 200 cm^-1 and 259 cm^-1. Scanning electron microscopy and energy dispersive X-ray spectroscopy measurements showed a significant loss of arsenic in the oxidized regions, but no erosion of the nanowire. Micro-photoluminescence measurements showed the near-band-edge emission of GaAs along the nanowire, as well as a new emission band at 755 nm corresponding to polycrystalline β-Ga₂O₃ formation. Our results also indicate that neither amorphous As nor crystalline As were deposited on the surface of the nanowire. Combining different experimental techniques, this study showed the formation of polycrystalline β-Ga₂O₃ by oxidation of the nanowire surface and the limits for performing spectroscopic investigations on individual GaAs NWs under ambient air conditions.