Spatial dependence of dopant incorporation and electrical transport in Si-doped GaAs(Sb) nanowires

Silicon (Si) impurities are among the most widely used dopants in GaAs-based electronic and optoelectronic materials, including low-dimensional systems such as nanowires (NWs). Undesired p-type conduction is often observed in Si-doped GaAs NWs due to the amphoteric nature of Si, but can be mitigated by proper catalyst-free, vapor-solid growth processes. Yet, the intriguing dynamics of Si dopant incorporation and spatial distribution within the NW structure are largely unknown, which are key to understanding the resulting electrical activity on a local scale. Here, we correlate the spatial distribution of Si dopants with the electrical transport characteristics of catalyst-free, selective-area grown GaAs(Sb) NWs. Through a combination of atom probe tomography, resonant Raman scattering, and single-NW field effect transistor measurements, spatial nonuniformities in Si concentration are revealed in both the axial and the radial directions. Si dopant gradients induced by the highly nonlinear growth rate along the NW axis result in varying rectifying current-voltage (I-V) characteristics with decreased conductivity (lower Si concentration) towards the NW tip. Surface segregation further leads to increased Si concentrations (up to ∼1020cm-3) on the surface of the GaAs(Sb) sidewalls, generating a thin parasitic region of high p-type conductivity. Finally, removal of the Si-enriched p-type surface region is demonstrated by controlled wet chemical etching in citric acid, revealing the intended n-type conduction of the bulk region of the NW.