Silicon technology has been the cornerstone for the advance of the current age of information since the
inception of the first transistor, due to an exponential development of microelectronics and chip
miniaturization. Based on this success, some of the emerging technologies in photovoltaics and quantum
computing are being developed using silicon nanowires as a fundamental building block. In the case of
photovoltaics, p-n axial and core-shell junctions in Si nanowires allow the integration of silicon technology
with other materials and thus a potential larger solar cell efficiency [1]. In quantum computing, silicon
nanowires serve as one of the semiconducting platforms for qubit development by controlling the electron
spin levels using a tailored selected doping and voltage in gates that split the nanowire into different quantum
dots [2]. In both scenarios it is of paramount importance to control several key parameters, among them the
dopant concentration in the nanowire, the stress, and the concentration of defects. They can all affect the
operation of the corresponding device and result in critical failure or lack of reliability. Accessing these
parameters with nanoscale resolution has been a challenge for spectroscopic techniques due to the diffraction
limit of currently widespread optical spectroscopy. We present here a characterization using micro-Raman
imaging and tip-enhanced Raman spectroscopy (TERS) that shows the potential of these techniques to
determine the doping profile of silicon nanowires in both p-n junctions and silicon nanostructures for qubits,
and to distinguish doping effects from others such as the presence of strain, crystal grains, and defects. High
dopant concentrations lead to Fano asymmetric line shape of the Raman spectrum of silicon with an
asymmetry parameter proportional to the dopant concentration and character – p- or n-type doping [3].
Confinement of the electric field due to the nanoscale diameter of the nanowires results in an enhancement of
the Raman signal that yields higher resolution than that expected without this antenna effect. This
enhancement allows us to employ micro-Raman spectroscopy successfully to distinguish several of the
above mentioned effects in nanostructures. In the case of p-n axial junctions in silicon nanowires, we observe
an asymmetry with higher spectral weight in the low and high energy side for p-type and n-type doping,
respectively, being the effect more pronounced in the case of p-type doping. This effect is more significant
for doping concentrations above 1017 cm-3. In the case of nanostructured silicon for qubits we observe
residual strain and crystallite grain boundaries close to the nanowire, tentatively attributed to the presence of
We analyze the Raman spectra employing several asymmetric functions and compare the results obtained in
nanowires with those reported in the literature and achieved in bulk silicon as a function of doping. Finally,
we employ TERS to reach nanoscale spatial resolution and compare the accuracy and limitations of
micro-Raman in the determination of the doping profile.
