RESUMO
InGaN/GaN double heterostructures and multiquantum wells (MQWs) have been successfully developed since more than 20 years for LED lightning applications. Recent developments show that state-of-the-art LEDs benefit from artificially generated V-pit defects. However, the control of structural and chemical properties plays a tremendous role. In this paper, we report on the lateral distribution of V-pit defects and photoluminescence of InGaN/GaN MQWs grown on thick GaN on patterned sapphire substrates. The synchrotron-based scanning X-ray diffraction microscopy technique K-map was employed to locally correlate these properties with the local tilt, strain, and composition of the InGaN/GaN MQW. Compositional fluctuation is the main factor for the variation of photoluminescence intensity and broadening. In turn, V-pit defects align along small-angle grain boundaries and their strain fields are identified as a reason for promoting the InGaN segregation process on a microscale.
RESUMO
This paper describes the application of phosphor-based light conversion for its use in optogenetic experiments to tailor the wavelength of light emitted from implantable miniaturized light sources. Gallium-nitride-based blue light-emitting diodes are used in combination with orthosilicate phosphor immersed in an epoxy matrix and emitting in the yellow wavelength range. The miniaturization of the phosphor-containing polymer droplets toward diameters as small as 300 µm provides the compatibility with implantable optical probes. The parameter study applied here varied the concentration of the phosphor material in the polymer matrix as well as the droplet height in order to tailor the characteristics of blue-to-yellow light conversion.