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Posted: Aug 09, 2017
Scalable nanowire photonic crystals
(Nanowerk News) Reporting their findings in Advanced Functional Materials ("Scalable Nanowire Photonic Crystals: Molding the Light Emission of InGaN"), researchers demonstrate the bottom-up synthesis of InGaN nanowire photonic crystals with precisely controlled size, spacing, and morphology, which can serve as the fundamental building blocks of a new generation of photonic crystal devices and systems.
Synthesizing InGaN nanowire photonic crystals via the bottom-up method, the formations of defects and dislocations are minimized due to the efficient surface strain relaxation.
With the use of selective area epitaxy, the team demonstrates that the size, spacing, and morphology of InGaN photonic crystals, including dot-in-nanowires, nanotriangles, and nanorectangles, can be precisely controlled, and, as such, spatially extended band edge modes can develop over a large area of such defect-free photonic crystals.
The researchers further observed that InGaN photonic crystals exhibit remarkably stable emission, compared to conventional InGaN light emitters. The luminescence emission, in terms of both the peak position (λ ∼ 505 nm) and spectral linewidths (full-width-half-maximum (FWHM) ∼ 12 nm), remained virtually invariant in the temperature range of 5–300 K and under excitation densities of 29 W cm-2 to 17.5 kW cm-2.
To appears to be the first demonstration of the absence of Varshni and quantum-confined Stark effects in wurtzite InGaN light emitters, factors that contribute significantly to the efficiency droop and device instability under high power operation.
Such distinct emission properties of InGaN photonic crystals stem directly from the highly stable and scalable band edge modes, due to the precisely controlled size, position, and morphology of InGaN nanowire photonic crystals, and are ideally suited for uncooled, high-efficiency LED, and laser operation.
"These unique characteristics, together with the scalable band edge optical mode, high light-extraction efficiency, on-demand beam characteristics, and full-color emission, render bottom-up GaN nanowire photonic crystals well suited for ultrahigh-efficiency, large-area LED and laser devices, as well as integrated nanophotonic circuits in the ultraviolet and visible spectral range," the authors conclude their report.