Gallium nitride (GaN) -based light-emitting diodes (LEDs) have been widely used in lighting, display, communication and other fields due to their high brightness, high luminous efficiency and low power consumption. Polarized LEDs have important potential application in flat panel display, holographic display and imaging fields. It’s very important to study how to realize efficient polarized LEDs. Realizing directional radiation (collimation) is one of the effective methods to improve the utilization efficiency of polarized light. In this paper, we proposed an all-dielectric (Al2O3/SiO2) films/(TiO2) grating nanostructures, and found that the enhanced emission of the polarized LED can be controlled within a specific angle by optimizing the parameters of the all-dielectric nanostructures. In particular, the simulation results show that the angular emission of polarized blue LEDs can be controlled within 11°, and the light output efficiency is more than 60% when the nanostructure is set as: Al2O3/SiO2 film thickness 70 nm, grating period 500 nm, line width 180 nm, and depth 100 nm. The peak light intensity is 5.2 times that of the bare LED. This nanostructure can be prepared easily and it has a large process tolerance. Our findings will provide the feasibility for achieving efficient polarized LEDs in display technology and imaging fields.
We proposed and demonstrated an integrated high energy efficient and high linearly polarized InGaN/GaN green LED grown on (0001) oriented sapphire with combined nanostructure converter and polarizer system. Different from those conventional polarized light emission generated with plasmonic metallic grating in which at least 50% high energy loss happens inherently due to high reflection of TE component of the electric field, a reflecting metasurface with 2D elliptic metal cylinder array (EMCA) that functions as a half-wave plate was integrated at the bottom of a LED such that the back-reflected TE component that is otherwise lost by a dielectric/metal bi-layered wire grids (DMBiWG) polarizer on the top emitting surface of the LED can be converted to desired TM polarized emission after reflecting from the metasurface, which significantly enhances the polarized light emission efficiency. Experimental results show that the extraction efficiency of the polarized emission can be increased by 40% on average in a wide angle of ±60° compared to that with naked bottom of sapphire substrate or 20% compared to that with reflecting Al film on the bottom of sapphire substrate while an extinction ratio (ER) of higher than 20 dB within an angle of ±60° can be simultaneously obtained directly from an InGaN/GaN LED. Our results show the possibility of simultaneously achieving high degree of polarization and high polarization extraction efficiency at integrated device level and advance the field of GaN LED toward energy efficiency, multi-functional applications in illumination, display, medicine, and light manipulation.
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