Infrared nanoscopy of strained semiconductors

Abstract

Knowledge about strain at the nanometre scale is essential for tailoring the mechanical and electronic properties of materials. Flaws, cracks and their local strain fields can be detrimental to the structural integrity of many solids. Conversely, the controlled straining of silicon can be used to improve the performance of electronic devices. Here, we demonstrate that infrared near-field microscopy allows direct, non-invasive mapping and a semiquantitative analysis of residual strain fields in polar semiconductor crystals with nanometre-scale resolution. Our experiments with silicon carbide crystals yield optical images of nanoindents showing strain features as small as 50 nm and the evolution of nanocracks. In addition, by imaging nanoindents in doped silicon, we provide experimental evidence for plasmon-assisted near-field imaging of free-carrier properties in nanoscale strain fields. Near-field infrared strain mapping provides possibilities for nanoscale material and device characterization, and could become a tool for nanoscale mapping of the local free-carrier mobility in strain-engineered semiconductors.

Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

“…The high intensities will also become useful to perform THz probe measurements in the near-field (Chan et al, 2007;Keilmann et al, 2009) using, for instance, scanning near field techniques utilizing metallic tips Huber et al, 2009) or nanometer apertures (Adam et al, 2008;Seo et al, 2009). Near-field measurements promise to resolve an issue we have not addressed so far: THz spectroscopy is suitable to probe charge carrier dynamics in nanoscale systems.…”

Nanoscale Conductivity Contrast by Scattering-Type Near-Field Optical Microscopy in the Visible, Infrared and THz Domains

“…Furthermore, the curve in Fig. 6 has taken the concentration dependence of τ (i.e., of the mobility) into account [39], with the resulting fit parameter n=4 10 19 cm −3 that agrees well with the design electron concentration [40].…”

“…A very interesting application of s-SNOM carrier density mapping has already been recently demonstrated: local conductivity in strained semiconductors including the technologically important Si [40]. In this study the complex near-field contrast was mapped in the neighborhood of permanent indents impressed by a sharp diamond tip, over the 890-1090 cm −1 frequency range.…”

“…The data points were extracted from a number of s-SNOM images taken consecutively at different wavelengths. The curve is from theory [40].…”

Widely tuneable scattering-type scanning near-field optical microscopy using pulsed quantum cascade lasers

“…A wide variety of applications have been demonstrated, ranging from mapping plasmonic resonances to chemical spectroscopy. [1][2][3][4][5][6][7][8] In an s-SNOM measurement, laser light is focused on to the apex of a very sharp metallic tip (typically of radius $10 nm). Depending on the polarization of this incident light, different sample properties can be measured.…”