Quantification of Carrier Density Gradients along Axially Doped Silicon Nanowires Using Infrared Nanoscopy

Doped semiconductor nanostructures are interesting for the fabrication of nanoscale electronic and photonic devices. Here, we use scattering-type scanning near-field optical microscopy (s-SNOM) to characterize axial carrier density gradients in phosphorus-doped silicon nanowires. We quantitatively determine the carrier density and length of the doped segment as well as the functional form of the charge carrier gradient in the transition region between doped and nominally undoped segments. These measurements are enabled by understanding and accounting for the influence of the native oxide on the near-field optical contrasts in the transition region. Our results are supported by correlative energy dispersive X-ray spectroscopy (EDS) measurements. This work demonstrates the ability of s-SNOM to directly probe nanoscale charge carrier density transitions through thin surface layers, a capability that is important for a variety of doped semiconductor systems.