The multiple light scattering of nanoporous (NP) GaN was systematically studied and applied to the color downconversion for micro-light-emitting diode (LED) display applications. The transport mean free path (TMFP) in NP GaN is 660 nm at 450 nm (light wavelength), and it decreases with a decreasing wavelength. It was observed that the short TMFP of the NP GaN increased the light extinction coefficient at 370 nm by 11 times. Colloidal QDs were loaded into a half 4″ wafer scale NP GaN, and 96 and 100% of light conversion efficiencies for green and red were achieved, respectively. By loading green and red QDs selectively into NP GaN mesas, we demonstrated the RGB microarrays based on the blue-violet pumping light with green and red color converting regions.
As the request for high resolution display is rising, it is imperative to develop the corresponding micro-LED technology to match this demand. In this paper, we demonstrate our latest efforts on color conversion patterning and seamless tiling for glass substrate. The color conversion can be achieved by colloidal quantum dots and we have patterns less than 10 microns deposited on LED chips. A continuous operation of more than 100 hours without linewidth broadening can be observed if quantum dots are well protected. The glass cutting technique was accomplished by optimized pulsed laser beam. The heat affected zone can be reduced from 100 to 15 microns. The resultant seamless tiling of the MicroLED on glass substrate can be demonstrated. These techniques can be useful for next generation of high end displays..
Indium phosphide (InP) quantum dots (QDs) with luminescence tunable over the entire visible spectrum were prepared by the conventional hot injection method. InP QDs are considered alternatives to Cadmium containing QDs for application in light-emitting devices because of showing similar optical properties to those containing toxic heavy metals. The multishell coating was shown to improve the photoluminescence quantum yield (QY) of InP QDs more strongly than the conventional ZnS shell coating. QY values were more than 60% along with FWHM of 41-73 nm can be routinely achieved, making the optical performance of InP/ZnS/ZnS or InP/ZnS/SiO2 QDs comparable to that of InP/ZnS QDs. These QDs and the polymer dissolved in the appropriate solvent and deposited by casting to give homogeneous films and showed a good level of dispersion of the QDs within the polymer.
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