Metasurfaces control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. However, all recent designs have exhibited concepts using geometrically fixed structures, or used materials with excessive propagation losses, thereby limiting potential applications. Here we show how to overcome these limitations using a reconfigurable hyperbolic metasurface comprising a heterostructure of isotopically enriched hexagonal boron nitride (hBN) in direct contact with a phase-change material (PCM), single crystal vanadium dioxide (VO2). Metallic and dielectric domains in VO2 provide spatially localized changes in the local dielectric environment to tune the wavelength of hyperbolic phonon polaritons (HPhPs) supported in hBN by a factor of 1.6. This contrasts with earlier work using surface phonon polaritons, where propagation could only be observed above a low-loss dielectric phase. We demonstrate the first realization of in-plane HPhP refraction, which obeys Snell’s law and the means for launching, reflecting and transmitting HPhPs at the PCM domain boundaries. To demonstrate practical applications of this platform, we show how hBN could be combined with either VO2 or GeSbTe glasses to make refractive nanophotonic waveguides and lenses. This approach offers control of in-plane HPhP propagation at the nanoscale and exemplifies a reconfigurable framework combining hyperbolic media and PCMs to design new optical functionalities including resonant cavities, beam steering and waveguiding.
Proc. SPIE. 9954, Fifteenth International Conference on Solid State Lighting and LED-based Illumination Systems
KEYWORDS: Infrared imaging, Spectroscopy, Dielectrics, Imaging spectroscopy, Near field scanning optical microscopy, Super resolution microscopy, Infrared radiation, Indium gallium nitride, Heterojunctions, Near field optics
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.
This contribution presents results on the structural and optoelectronic properties of InN layers grown on AlN/sapphire
(0001) templates by Migration-Enhanced Plasma Assisted Metal Organic Chemical Vapor Deposition (MEPAMOCVD).
The AlN nucleation layer (NL) was varied to assess the physical properties of the InN layers. For ex-situ
analysis of the deposited structures, Raman spectroscopy, Atomic Force Microscopy (AFM), and Fourier Transform
Infrared (FTIR) reflectance spectroscopy have been utilized. The structural and optoelectronic properties are assessed by
Raman-E2 high FWHM values, surface roughness, free carrier concentrations, mobility of the free carriers, and high
frequency dielectric function. This study focus on optimizing the AlN nucleation layer (e.g. temporal precursor
exposure, nitrogen plasma exposure, plasma power and AlN buffer growth temperature) and its effect on the InN layer
This paper presents optoelectronic and structural layer properties of InN and InGaN epilayers grown on sapphire templates by Migration-Enhanced Plasma Assisted Metal Organic Chemical Vapor Deposition (MEPA-MOCVD). Real-time characterization techniques have been applied during the growth process to gain insight of the plasma-assisted decomposition of the nitrogen precursor and associated growth surface processes. Analyzed Plasma Emission Spectroscopy (PES) and UV Absorption Spectroscopy (UVAS) provide detection and concentrations of plasma generated active species (N*/NH*/NHx*). Various precursors have been used to assess the nitrogen-active fragments that are directed from the hollow cathode plasma tube to the growth surface. The in-situ diagnostics results are supplemented with ex-situ materials structures investigation results of nanoscale structures using Scanning Near-field Optical Microscopy (SNOM). The structural properties have been analyzed by Raman spectroscopy and Fourier transform infrared (FTIR) reflectance. The Optoelectronic and optical properties were extracted by modeling the FTIR reflectance (e.g. free carrier concentration, high frequency dielectric constant, mobility) and optical absorption spectroscopy. The correlation and comparison between the in-situ metrology results with the ex-situ nano-structural and optoelectronic layer properties provides insides into the growth mechanism on how plasma-activated nitrogen-fragments can be utilized as nitrogen precursor for group III-nitride growth. The here assessed growth process parameter focus on the temporal precursor exposure of the growth surface, the reactor pressure, substrate temperature and their effects of the properties of the InN and InGaN epilayers.