Holographic gratings have been fabricated in networked polyurethane
acrylates with various cross-linking densities. It was found that low
(f = 2) and
high (f = 6) functionality monomers gave narrow and clean polymer–liquid crystal
(LC) phase separation due presumably to the insufficient migration of LC
molecules out of the polymer domains. However, the mechanisms leading
to poor phase separation seem different, i.e., reaction at a slow rate for
f = 2, and entrapment of LC molecules within highly networked polymer for
f = 6. With intermediate
monomer functionality (f = 3), relatively large channels with large LC droplets gave the greatest diffraction
due to a large difference in refractive index between polymer and LC phases.
Interfacial microstructure and elemental diffusion of Cu-doped indium oxide (CIO)/indium tin oxide (ITO) ohmic contacts to p-type GaN for light-emitting diodes (LEDs) were investigated using cross-sectional transmission electron microscopy (XTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. The CIO/ITO contacts gave specific contact resistances of approximately 10(-4) omegacm2 and transmittance greater than 95% at a wavelength of 405 nm when annealed at 630 degrees C for 1 min in air. After annealing at 630 degrees C, multi-component oxides composed of Ga2O3-In2O3, Ga2O3-CuO, and In2O3-CuO formed at the interface between p-GaN and ITO. Formation of multi-component oxides reduced the barrier height between p-GaN and ITO due to their higher work functions than that of ITO, and caused Ga in the GaN to diffuse into the CIO/ITO layer, followed by generation of acceptor-like Ga vacancies near the GaN surface, which lowered contact resistivity of the CIO/ITO contacts to p-GaN after the annealing.
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