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.
The concepts, features, modeling and practical realizations of high power high brightness semiconductor diode lasers
having ultrathick and ultrabroad waveguides and emitting in the single vertical single lateral mode are analyzed.
Ultrathick vertical waveguide can be realized as a photonic band crystal with an embedded filter of high order modes. In
a second approach a tilted wave laser enables leakage of the optical wave from the active waveguide to the substrate and
additional feedback from the back substrate side. Both designs provide high power and low divergence in the fast and the
slow axis, and hence an increased brightness. Lateral photonic crystal enables coherent coupling of individual lasers and
the mode expansion over an ultrabroad lateral waveguide. Experimental results are presented. Obtained results
demonstrate a possibility for further expansion of the concept and using the single mode diodes having an ultrabroad
waveguide to construct single mode laser bars and stacks.
We have designed, fabricated and measured the performance of two types of edge emitting lasers with unconventional
waveguides and lateral arrays thereof. Both designs provide high power and low divergence in the fast and the slow axis,
and hence an increased brightness. The devices are extremely promising for new laser systems required for many
scientific and commercial applications. In the first approach we use a broad photonic crystal waveguide with an
embedded higher order mode filter, allowing us to expand the ground mode across the entire waveguide. A very narrow
vertical far field of ~ 7° is resulting. 980 nm single mode lasers show in continuous wave operation more than 2 W,
ηwp ~ 60%, M2 ~ 1.5, beam parameter product of 0.47 mm×mrad and a brightness ~ 1×108 Wsr-1cm-2 respectively. First
results on coherent coupling of several lasers are presented. In the second approach we use leaky designs with feedback.
The mode leaks from a conventional waveguide into a transparent substrate and reflects back, such that only one mode at
a selected wavelength is enhanced and builds up, others are suppressed by interference. 1060 nm range devices
demonstrate an extremely narrow vertical far field divergence of less than 1°.