Infrared nanoscopy of In-rich InGaN epilayers(Conference Presentation)

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.