Full wafer microstructure fabrication by continuous UV-assisted roller imprinting lithography to enhance light extraction of LEDs

The ratio of the number of emitted photons from the active region of LEDs to the number of photons escaping to free space (light extraction efficiency) constitutes an essential figure for judging the performance of an LED. Fresnel loss occurs between LEDs, and air is an unavoidable factor for influencing light extraction, though the main loss channel in the LED is caused by the total internal reflection (TIR). Surface texturing ruins the TIR, and therefore enhances light extraction efficiency. This study performed UV-assisted roller imprinting to build periodical microstructures on the surface of LEDs. The results showed that the output power enhancements for LEDs with imprinting micro-cylinders at heights of 0.5, 1, 1.5, 2.5, and 5 μm were greater than conventional LEDs at 100 mA current injection by 18.79%, 25.11%, 26.34%, 22.12%, and 8.87%, respectively. The numerical simulation performed using the ray tracing method was also useful for obtaining the microstructure with optimal light efficiency extraction. The 2″ full wafer imprinting was fabricated through the flexible mold adopted by reversal imprinting.

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► We performed UV-assisted roller imprinting to build microstructures on the LEDs.
► These microstructures helped more photons inside the LEDs escape into free space.
► The experiments showed greatly enhanced extraction efficiencies for imprinting LEDs.
► The simulation was useful to obtain the microstructure with efficiency extraction.