Polarization Transmission Of Surface Nanostructure On GaN-based LED

Being integrated on the emitting surface of GaN based LED for increasing the lightextraction efficiency and enhancing the polarization transmission, the subwavelengthmetal grating has been developed rapidly in recent years. The multi-functional GaNbased LED with polarized light emitting has potential applications in flat-panel displayand optoelectronic devices which is in great demands in optoelectric industry, integratedphotonic and the display technology.The characteristics and fabrication of GaN-based LED with integrated surfacesubwavelength structure are investigated in the paper. The main contents are as follows:1．The GaN multilayer structure is analyzed and optimized by using the equivalentmedium theory in order to control the light transmission and enhance the opticalproperties. Then the FDTD method was used to study the GaN-based LED withembedded composite grating structure. The material properties and physical dimensionare investigated, including refractive index of the structural components, height of thetransition layer, the grating period, duty cycle and depth. It is found that both TMtransmission and the extinction ratio of the LED output can be effectively enhanced byincorporating a dielectric transition layer between the composite grating and GaNsubstrate in the blue and green band.2．Two kinds of polarized nanostructure are designed and optimized on LED surface.(1)The air-gap polarization grating. As the energy localization within the air gap and theenhancement of the near field coupling, such a subwavelength metal grating allows mostof the TM polarization through. The TM transmission is up to more than88%and ER isup to more than37dB in visible spectrum practically. The grating period can be designed larger than200nm.(2)The nano-particle array grating. This nanostructure enables simplefabrication, since the novel arrays can be directly coated on the surface of GaN. ER up to26dB and a TM polarized transmittance of84%are achieved in the green band.3．The fabrization processes of the subwavelength metal grating have been introduced,including the lift-off technique based on traditional photolithography and the holographicion beam etching process. Using the lazer interference lithography and the lift-offtechnique, we preliminary fabricate a metal grating structure with a grating period of330nm. Finally the morphology of grating mask and the polarization performance aremeasured.