Quantitative Local Conductivity Imaging of Semiconductors Using Near-Field Optical Microscopy

Abstract

We demonstrate contactless, nanoscale measurements of local conductivity, free carrier density, and mobility using phase-resolved infrared (IR) scattering-type near-field optical microscopy (s-SNOM). Our approach extracts quantitative conductivity information by combining analytical and finite-element methods to predict the scattered near-field amplitude and phase for specific sample geometries, without relying on bulk mobility assumptions or empirical fitting parameters. We find that the finite-dipole model (FDM) overestimates the expected near-field amplitude and phase in nonplanar or nanostructured materials, so we employ finite-element modeling to choose appropriate corrections to the FDM and account for sample geometry. The model is validated using a silicon calibration sample, and our results return the free carrier concentration expected based on the encoded dopant profile. Mobility and conductivity are also found to be in good agreement with established models for bulk silicon. This work demonstrates the potential of IR s-SNOM to perform quantitative local conductivity measurements, including the separation of free carrier density and electronic mobility, and represents a step toward the goal of quantitative carrier profiling and mobility mapping using s-SNOM.

Characterization of Modified PVDF Membranes Using Fourier Transform Infrared and Raman Microscopy and Infrared Nanoimaging: Challenges and Advantages of Individual Methods

“…For further details about the principles of this technique, kindly refer to the cited literature. − The schematic experimental setup can be seen in Figure S1 in the Supporting Information. Nowadays, IR-sSNOM plays a priceless role in numerous scientific fields including, for example, semiconductor research, − physical chemistry, biophysical chemistry, or the previously mentioned polymer-related application fields. , …”

Polarization Sensitivity in Scattering-Type Scanning Near-Field Optical Microscopy—Towards Nanoellipsometry

“…Since it is a versatile tool for optical surface characterization and analysis, scatteringtype scanning near-field optical microscopy (s-SNOM) has been broadly applied to various material systems, ranging from single crystals [1] to thin films [2], heterostructures [3], semiconductors [4], and biological samples [5]. Generally, s-SNOM can be performed at any wavelength [6][7][8][9][10][11], and thus the near-field response strongly depends on the sample's optical characteristics, i.e., frequency-dependent polarizability.…”

Nanophotonics for Chemical Imaging and Spectroscopy

“…Photothermal, infrared, and nonlinear spectroscopy and microscopy approaches are an integral part of this VSI. Indeed, various flavors of photothermal microscopy and nanoscopy, , unique applications of infrared-based near-field optical microscopy and spectroscopy, , and coherent Raman-based nanoimaging and nanospectroscopy studies are described . In the latter, reproducible enhanced molecular coherent anti-Stokes Raman scattering (CARS) was reported, using a (gently irradiated) Si particle on a mirror platform.…”