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Group III-V semiconductor nanostructures have been at the forefront of numerous
applications in high-power, high frequency optical and optoelectronic devices.
Although, significant progress has been made in fabrication and characterization of
these materials, there are still challenges in the formation of compositional uniform
indium-rich ternary epilayers, embedded in wide bandgap III-N’s. For example,
nanoscale lateral compositional inhomogeneities at the growth surface lead to bulk
phase segregations will reduce the structural quality of the semiconductor
heterostructures both in macro and nanometer scales if not controlled through the
process parameter space at the surface. Studying and understanding the fundamental
physical and structural properties at the nanoscale level and correlating the findings
with processing parameters is essential to mitigate compositional fluctuations in
multinary III-N compounds. In this work we introduce infrared scattering type
scanning near-field microscopy (s-SNOM) for spectroscopic study of nanoscale
optical properties of InGaN epilayers on GaN- or InN templates. S-SNOM possesses
spatial resolution of few nanometers (~15 nm) far below the diffraction limit and
allows spectroscopic imaging of simultaneous chemical and structural information
correlated with morphology. We correlate s-SNOM near-field amplitude and phase
optical contrasts at infrared frequencies to the dielectric constants and growth
parameters of InN/InGaN heterostructures and/or single nanoparticles. We observed
that both the real and imaginary dielectric function values of mono-/bi-layers of
InN/InGaN can be extracted from s-SNOM data. By performing nano-spectroscopy
on lithographically patterned samples, we also show that self-assembled InGaN
nanoparticles have similar dielectric function values as that of thin film InGaN.
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